MINERAL AND WATER RESOURCES
OF MONTANA

Water Resources


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(By Frank Stermitz, Helena, Mont., T. F. Hanly, Worland, Wyo., and C. W. Lane, Billings, Mont., U.S. Geological Survey)

SURFACE WATER
GROUND WATER
UTILIZATION & STORAGE
BASIN APPRAISALS
REFERENCES

 

INTRODUCTION

An abundant supply of water prevails over much of Montana, particularly in the mountain areas and adjacent to the major watercourses. Surface-water supplies are of good quality in the mountain areas but are variable in both quantity and quality in the plains area. Ground-water supplies adequate for stock and domestic use are available in most of the State. Large ground-water supplies of good quality are generally available in the intermontane valleys and near major streams but are lacking in much of the plains area. Reservoir storage has greatly aided utilization of surface water for irrigation and electric-power generation. Large-scale development of the State's ground-water resources has only begun, and many opportunities exist for development and further utilization.

The climate of Montana deserves brief description as available water originates in the State or bordering areas of similar climatic characteristics. The mean annual precipitation is about 15 inches. It is heavy in the mountains and light in the foothills and plains. Figure 45, prepared by the U.S. Weather Bureau, shows the areal distribution of precipitation. NOTE: for this digital edition, a precipitation map from the Montana Dept. of Agriculture is used and is shown below. Although the indicated range is from 6 to 56 inches, half of the State lies in the belt of 12 to 14 inches. About 60 percent of the annual precipitation in the high mountain areas occurs during the snow storage period of late October to early April. In the foothills and plains areas east of the Continental Divide, 65 to 80 percent of the precipitation occurs during the April to September period. The April to September precipitation in the mountain valleys west of the Continental Divide varies considerably and averages about half the annual amount. Winter temperatures are conducive to snow storage in the high mountains. Chinook or thawing winds of midwinter often deplete snow storage on the foothills and plains.

Chemical quality and sediment are factors that affect the water resources. In Montana the natural effects are hardness and variations in chemical and sediment content. Man's actions in the use of water result in problems involving irrigation return flows, sediment in reservoirs, and domestic and industrial wastes.

Man's actions such as disposing of domestic, industrial, and radioactive wastes can be controlled. Other problems such as return flows from irrigation, and reservoir sedimentation can be minimized by adequate planning and design of facilities.

Montana employs the doctrine of prior appropriation for the administration of water rights. These rights which are also based upon the application of the water to beneficial use, are administered under supervision of district courts. Legislation that became effective January 1, 1962, places the administration of ground-water rights in the office of the State Engineer.

The water crossing the international boundary is subject to the general provisions of the Boundary Waters Treaty of 1907 and subsequent orders of the International Joint Commission. The latter are of particular significance on the Milk and St. Mary Rivers where definite apportionment is practiced. Interstate tributaries of the Yellowstone River are allocated by the Yellowstone River Compact.

SURFACE WATER

The surface water of Montana drains to the Pacific Ocean, the Gulf of Mexico, and Hudson Bay. There are a few small closed basins near the northern border east of the Continental Divide and northwest of Billings. The relative discharge of the principal streams is shown in the schematic map of figure 46. The line width of streams represents the mean discharge. The width is varied as the square root of the discharge to permit visualization of major streams throughout their length. The streams entering Montana contribute about 21,000 cubic feet per second as an average and those leaving the State discharge an average of about 58,000 cubic feet per second. About 5,000 cubic feet per second is used consumptively in the State. The Columbia River basin constitutes 17 percent of the area of the State and has 58 percent of the total streamflow of 63,000 cubic feet per second. Approximately 82 percent of the State lies in the Missouri River basin and has 40 percent of the water supply. The Hudson Bay drainage area comprises less than half of 1 percent of the drainage area of the State and has about 2 percent of the streamflow.

A common measure of water for irrigation is the acre-foot, which is the volume required to cover an acre to the depth of 1 foot, and is equivalent to 326,000 gallons. A flow of 1 cubic foot per second is equal to 449 gallons per minute, 1.98 acre-feet per day, or about 724 acre-feet per year.

The mean annual runoff varies from more than 40 inches to less than 0.25 inch and averages about 3.5 inches for the State. The areal distribution as equivalent inches of depth over the land surface is shown generalized in figure 47. The generally mountainous areas west and east of the Continental Divide have relatively high runoff. About half the State has less than 1 inch of runoff.

The usefulness of streamflow is related to its seasonal and annual dependability. The large proportion of the annual precipitation that falls on the high mountains during the winter or snow-storage months has a marked effect on the runoff pattern. The snow-melt runoff from the mountains begins in April and reaches a peak rate in late May or earls June. The runoff is essentially completed in July and the normal baseflow recession is modified slightly by summer rains. As vegetative uses decline and the fall rams begin, another increase in flow occurs before cold weather restricts streamflow to the groundwater outflow rate. In some winters, mild weather may bring about a brief increase in streamflow. The sustained minimum flows of the mountain streams generally occur during March when ground-water outflow reaches its lowest level. To illustrate this flow pattern, typical annual hydrographs for the Flathead River near Columbia Falls and the Yellowstone River at Corwin Springs are shown in figure 48. The latter stream passes through Yellowstone Lake and a smoother pattern of runoff is apparent from its hydrograph. The variability of annual flow is relatively small for most mountain streams. Annual discharges for the Clark Fork at St. Regis fall within plus 56 percent and minus 52 percent of the average discharge during the index period of 1931-60. A similar comparison for the Yellowstone River at Corwin Springs shows variations of plus 44 percent and minus 36 percent. Most of the low flows occurred during the general drought period of the 1930's.

Streams of the foothills and plains areas are usually at extremely low level or may cease flowing during the winter. The melt of snow and channel ice accumulated during the winter usually takes place in late March, although brief thaws as early as February are not uncommon. The spring rise may produce the peak flow of the year. The recession from the peak is quite rapid and subsequent increases in flow are dependent upon rains of sufficient intensity and duration to cause surface runoff. These streams may cease flowing during the hottest part of the summer, and resume flowing as evaporative and vegetative losses decrease. An annual hydrograph for Marias River near Shelby (fig. 48) shows the mixed influence of a mountain and foothill environment. The hydrograph for the Poplar River near Poplar (fig. 48) is typical of the plains streams, wherein variations in flow are the greatest. The annual discharges for the Marias River near Shelby fall within plus 89 percent and minus 62 percent of the average discharge for the index period of 1931-60. The lack of complete record before 1947 requires the use of a 1947-60 period for comparison of the variability of flows of the Poplar River near Poplar. During that shorter time period, the annual discharges lie within plus 173 percent and minus 77 percent of the average.

Few data are available to indicate the chemical quality of water in the Columbia River Basin in Montana. Based on these few data and on the geology of the area, it seems probable that the water is generally a calcium bicarbonate type with relatively low concentrations of dissolved solids. This type of water is also general in the Missouri River Basin upstream from Fort Peck Reservoir, and in the Yellowstone River Basin upstream from Billings. An exception is the Teton River below Priest Butte Lake drain, where the water is a sodium sulfate type with relatively high concentrations of dissolved solids. The water of the lower Missouri River, including Fort Peck Reservoir, the Milk River downstream from Havre, and the northern tributaries to the Missouri River below Fort Peck Reservoir, is a sodium bicarbonate type with relatively high concentrations of dissolved solids. Downstream from Billings the water of the Yellowstone River and its tributaries is a sodium sulfate type with relatively high concentrations of dissolved solids. Figure 49 shows the general distribution of the water-quality types and the approximate range in the concentration of dissolved solids.

The sediment yield of Montana streams varies with geology, relief, stream velocity, vegetation in the drainage basin, precipitation, and abundance of flow. Some geologic formations such as shales and soft sandstones are easily eroded and are large producers of sediment. Transportation of sediment by flowing water is a natural geologic process that has been accelerated by man's actions.

Few data are available to indicate either the long term or the annual sediment yield in the Columbia River Basin in Montana. However, the few observations and a knowledge of the geology of the area indicate a relatively low sediment yield except in localities where mining and lumbering operations are active. This is also true throughout the upper Missouri River Basin and upper Yellowstone River Basin where more data are available. Farther east, where the surficial rocks are predominantly shales and soft sandstones, the sediment yield is relatively high. In the north-central part of Montana, streams flowing in Bearpaw shale have the highest sediment yield observed in the State. The general areas and rates of sediment yield are delineated on figure 50.

The temperature of flowing streams during the winter period is near the freezing point. After the disappearance of channel ice in late March or early April, stream temperatures show a gradual rise to as high as 50° F. by late April. The water temperatures may drop to less than 40° F. as the mountain snowmelt progresses, according to the relative contribution of snowmelt runoff to streamflow. Another warming trend begins in June as snowmelt runoff decreases. Water temperatures are generally between 60° F. and 70° F. in July and August. Temperatures as high as 80° F. have been measured on small streams in the plains area during periods of prolonged hot weather. A gradual downward trend in water temperatures usually begins by early September and the near freezing point is common by late November. The temperature of water released from large storage reservoirs approaches the mean annual air temperature.

GROUND WATER

Most of western Montana is mountainous but contains numerous large intermontane valleys. The mountains are composed principally of Precambrian crystalline and Tertiary igneous rocks but also include some rocks of Paleozoic and Mesozoic age. These rocks are not sources of ground water but do serve as catchment areas for precipitation, a part of which later enters the pervious fill of the intermontane valleys to become ground water.

The fill underlying many of the intermontane valleys is quite thick, as much as several thousand feet in some valleys, and is composed of Cenozoic alluvium and lakebeds. The sediments filling many of these valleys are very permeable and form vast ground-water reservoirs, most of which are almost completely filled. Recharge of the ground water is by precipitation in the valleys, seepage of applied irrigation water, and seepage from streams. During periods of low flow in the major streams, ground water is discharged to the streams providing the base streamflow.

East of the Rocky Mountains, in a broad belt extending through the central part of the State, is an area of high plains broken by isolated mountain ranges. Most of the area is underlain by stratified rocks of Paleozoic and Mesozoic age. The rocks contain a number of sandstone and limestone formations that are permeable and contain large quantities of ground water. Many of the water-bearing rocks are exposed on the flanks of the isolated mountains, and thus are favorably situated to receive recharge from precipitation and from streams flowing from the mountains. Many of the water-bearing rocks are deeply buried away from the mountains, and the geologic structure is such that flowing artesian wells can be obtained in some areas.

The Fort Union formation and high terrace gravels of Cenozoic age are present over sizable but isolated areas in the central part of the State. These rocks are generally very permeable, and, where thick enough, are sources of ground water.

Most of Montana east of the isolated mountains is a high plain devoid of mountains but deeply incised by the Missouri and Yellowstone Rivers and their tributaries. Erosion adjacent to the streams gives considerable topographic relief to the area locally. In most of eastern Montana the Fort Union formation of Cenozoic age underlies the surface and is, underlain by several thousand feet of Paleozoic and Mesozoic stratified rocks. Only the Mesozoic and Cenozoic rocks of eastern Montana are significant as sources of ground water, the older rocks being too deeply buried to be within economic drilling depth for water wells. Geologic structural conditions are favorable in parts of eastern Montana for obtaining flowing artesian wells. Most notable of the artesian areas are at low elevations in the Tongue, Powder, and lower Yellowstone River drainage basins. Ground water recharge in the eastern part of the State is by precipitation in the area, and owing to the semiarid climate, is probably quite small.

The image below (from USGS) shows how ground water occurs in rocks.

Of great significance to the ground-water supply of the State are the alluvium and low terrace deposits in the inner valleys of most streams in the State. The alluvium and terrace deposits are composed principally of silt, sand, gravel, and cobbles and are the most permeable water-bearing rocks in the State. The deposits are readily recharged by precipitation, by streams during periods of high stage, and by applied irrigation water.

Unconsolidated deposits of silt, clay, sand, and gravel underlie the intermontane valleys of the West, are present in the valleys of most of the major streams, and mantle the consolidated bedrock in many parts of the State. The unconsolidated deposits generally contain an abundant supply of ground water. Development of this valuable resource for other than domestic and stock use has started in only a few areas of the State. Figure 51 shows the magnitude of the groundwater supplies that can be developed from wells in the unconsolidated rock deposits in various parts of the State. The areas shown are those in which wells within the indicated range of yield are known to be present. The indicated well yields may not be available at all locations within the areas shown, but the potential for such well yields is favorable. Moderate to large well yields from unconsolidated rocks may be available in other parts of the State but are not yet known.

The consolidated rocks of significance to the ground-water supply are the stratified rocks underlying most of the area east of the Rocky Mountains. Within this vast area, wells in the consolidated rocks provide water supplies for many towns, some industries, and a large percent of the domestic and stock use. There are many rock formations that are water bearing, but owing to the complexity of the geology, not all the formations will be found in any given area, and the depth of well required to tap a given formation will vary with location. The rock formations are nearly all named, and those yielding ground water are usually known to well drillers and to many residents of an area where they are utilized. The rock formation names common to individual areas will be used to describe the source and availability of ground water in the section that follows.

The quality of ground water in Montana varies greatly in chemical characteristics and dissolved-solids content. These variations depend mainly on the geology and the precipitation of an area. The Cenozoic and Mesozoic sedimentary rocks of eastern Montana yield water that is of poorer quality than the water obtained from the deposits in the intermontane valleys of western Montana. Water obtained from a geologic source in western Montana tends to be more uniform in chemical character and mineralization, whereas in eastern Montana considerable variation occurs in the quality of water obtained from any given formation, depending upon location and depth to supply. The igneous and metasedimentary bedrock of western Montana, with some exceptions, is much more dense than the Cenozoic and Mesozoic rocks of eastern Montana, and as a consequence, the soluble minerals are not as readily leached and thus do not contribute greatly to the mineralization of the ground water. The chemical quality of ground water in eastern Montana shows considerable variation. The permeability and recharge characteristics of the rocks in this part of the State permit the contained water a longer but variable contact time to dissolve the available minerals.

UTILIZATION AND STORAGE

Irrigation throughout the State comprises most of the consumptive water use. Data from various sources indicate that generally more than 1,500,000 acres are irrigated annually with reasonably adequate water supplies. About 500,000 additional acres of pasture, wild hay, and early maturing crops are inadequately irrigated from intermittent or overappropriated streams. This latter acreage includes flood-irrigation and water-spreading projects that may receive little or no water in an unfavorable season. Numerous reservoirs provide a usable capacity of about 1,300,000 acre-feet exclusively for irrigation. The use of ground water for primary or supplemental irrigation has made a modest beginning in a few areas. This use, which constitutes less than 1 percent of the irrigation diversion, has been primarily in the intermontane valleys or in alluvial valleys where recharge from streams could be expected. Many of the irrigation enterprises are operated by individuals or small organizations, and information on quantities of water diverted, lost by conveyance, applied, and returned, are too incomplete to arrive at reliable data on water usage. Gross diversion may be as much as 10 million acre-feet annually, of which about 2,500,000 acre-feet is consumed or is lost by evaporation and transpiration. Some return flows are reused for irrigation downstream. The regimen of a few streams is sufficiently altered by Irrigation use to lower the normal high water period of May and June, and the highest flow months may be in the late fall.

The significant use of surface and ground water for livestock has a high economic value. In many areas, the scarcity of water limits use of the range for this purpose. The quantity used for livestock, including evaporation loss from stock ponds, exceeds that used by municipalities. The evaporation loss from shallow stock ponds is several times greater than consumption by livestock from this source.

The municipal and industrial uses of water are respectively about 113 and 204 million gallons per day. This annual diversion is about 350,000 acre-feet or less than 1 percent of the average surface supply. Ground water is used exclusively by 92 municipalities; 40 are supplied by surface water and 19 use combinations of surface and ground water. Nearly 55 percent of the State's population is supplied by surface water of good quality. Ground water is the primary source of rural, domestic, and stock water supplies. About 80 percent of the commercial and industrial use is supplied from surface water sources.

Although the variability of annual flow of many Montana streams is relatively small, storage and redistribution to meet demands is essential to achieve a reasonable degree of utilization. The early storage facilities were based upon the single-purpose concept and were generally small and readily constructed. The application of the multi-purpose approach and the consideration of benefits beyond the borders of the State has been a growing factor in recent major storage developments. The capacity of present surface storage facilities is about 28 million acre-feet, equal to two-thirds of the average annual runoff. However, the greater part of that storage is concentrated on a few streams and does not provide the degree of control within Montana that might be implied.

Flathead Lake, Montana, U.S.A. May 1985. The irregular shoreline of Flathead Lake is discernible in this northeast-looking, low-oblique photograph. The lake [30 miles (48 kilometers) long and 12 to 14 miles (19 to 23 kilometers) wide], located in a depression that remained after a large block of ice retreated during the last ice age, is used for recreation and some irrigation. Kalispell is barely discernible north of the lake. East of the lake are the snow-covered, rugged peaks of the Mission Range, east of which is elongated, glacier-carved Swan Valley. Clouds overhang the peaks of the Swan Range, which is east of Swan Valley. To the east-northeast of Flathead Lake is Swan Lake, and to the west are the lower, less rugged Salish Mountains. Agricultural field patterns appear south of the lake in Flathead Valley. (NASA photo)
There are 59 reservoirs in Montana, each with a capacity in excess of 5,000 acre-feet. The 48 reservoirs devoted exclusively to irrigation have a combined capacity of 1,300,000 acre-feet and generally are on or are supplied by the smaller streams. The reservoirs with a capacity in excess of one-half-million acre-feet each are Hungry Horse and Flathead Lake in the Columbia River Basin, and Canyon Ferry, Tiber, and Fort Peck in the Missouri River Basin. Hungry Horse Reservoir, on the South Fork Flathead River near Columbia Falls, has a usable capacity of 3,428,000 acre-feet for onsite power generation and flood control and for downstream hydroelectric power. The control of Flathead Lake through a range in stage of 10 feet provides 1,219,000 acre-feet of storage for hydroelectric power. Canyon Ferry on the Missouri River near Helena has a usable capacity of 2,043,000 acre-feet. Its primary use is for the reregulation of streamflow to supply prior downstream water rights, thus permitting an expansion of upstream irrigation. Onsite generation of hydroelectric power, municipal supply, and local irrigation are also involved. Tiber Reservoir, on Marias River near Chester, has a usable capacity of 1,313,000 acre-feet at controlled spillway elevation. It was designed for irrigation water storage as well as flood control, recreation, and stream regulation purposes which it now serves. Fort Peck Reservoir, on the Missouri River in northeastern Montana, has a usable capacity of 17,800,000 acre-feet for power generation, flood control, navigation, and downstream regulation of flows. This storage capacity is nearly triple the mean annual flow at the site. Yellowtail Reservoir is now (1963) being constructed on the Bighorn River south of Hardin in the Yellowstone River Basin. It will have a usable capacity of 1,375,000 acre-feet for power generation, irrigation, hood control, and sediment storage. This storage capacity is nearly twice the mean annual flow at the site.

Various State and Federal agencies and private interests have proposed additional reservoirs having a total capacity of 14 million acre-feet of water, about equally divided between the Columbia and Missouri River Basins. The choice of alternate plans might greatly increase or decrease the proposed storage.

The evaporation from surface reservoirs significantly alters the available water supply. It has been estimated that an average of more than 2 million acre-feet of water is evaporated each year from the reservoirs, lakes, and streams in Montana (Meyers, 1962), as follows:

From principal reservoirs and regulated lakes
with usable storage of 5,000 acre-feet or more ---------1,294,000 acre-feet

From other large nonregulated lakes, with surface
area of 500 acres or more ------------------------------137,000 acre-feet

From principal streams and canals-----------------------291,000 acre-feet

From small reservoirs, lakes, and stock ponds-----------256,000 acre-feet

From small streams--------------------------------------121,000 acre-feet

Total for Montana-------------------------------------- 2,099,000 acre-feet

Annual evaporation rates range from less than 24 inches in the higher mountains to about 40 inches in the southeastern plains.

The storage of waters by recharge of aquifers may prove feasible in some places. Such storage generally would not interfere with present land uses and evaporative loss would be greatly reduced. Some use of the artificial recharge that occurs through irrigation in intermontane valleys has been made, and an appreciable effect is apparent on the streamflow regimen.

The numerous streams, lakes, and reservoirs are utilized by residents and visitors for various forms of recreation. The social and economic values are recognized and given consideration in development plans. Campers and picnickers are particularly attracted to mountain areas. The good chemical quality, suitable temperatures, low sediment content, and sustained flow of streams in the western two-thirds of the State promote good trout habitat. The natural lakes and the reservoirs are used extensively for water-based sports, and many homes have been built on the shores. A significant number of natural or artificial water bodies are used as refuges for migratory fowl. The tourist business ranks third in economic value in the State and the water resources play an important part in attracting visitors.

The development of reasonably firm power on Montana streams requires considerable storage capacity to redistribute variable seasonal flows for less variable power-generation needs. The runoff of mountain streams during May and June ranges from 45 to 60 percent of their total annual flow, depending mainly upon geographic location and altitude of the watershed. The runoff for April through July is about 65 to 75 percent of the annual flow. As the mountain streams traverse the plains areas, the incremental inflow tends to lengthen the high-flow periods and to increase the percentage of flow during the remaining months. Irrigation is also an important factor toward equalization of seasonal streamflow. Multipurpose storage for flood control, irrigation, recreation, downstream navigation, industrial and municipal supply, and fish and wildlife should be considered in power development plans.

The installed power capacity of each stream in the principal river basins is shown in table 9. The installed power capacity in kilowatts represents the manufacturer's rating of the maximum power output from the generating equipment. The average annual power produced is given in terms of kilowatt-hours as reported by the Federal Power Commission in 1960. The average power generation in the State is reported to be 59 percent of the installed capacity.

Table 9. Installed capacity and average yearly power data for existing projects in Montana
STREAM Existing installed
capacity (kilowatts)
Percent of
State total
Existing average
power (kilowatts)
Percent of
State total
Columbia River Basin:        
 Lake Creek 4,500 0.36 2,854 0.39
 Flint Creek 1,100 0.09 913 0.12
 Clark Fork 315,920 25.04 186,073 25.23
 South Fork, Flathead 285,000 22.58 94,406 12.80
 Swan River 4,150 0.33 3,539 0.48
 Big Creek 360 0.03 126 0.02
 Flathead River 168,000 13.31 121,005 16.41
TOTAL, Columbia River Basin 779,030 61.74 408,916 55.45
Missouri River Basin:        
 Missouri (main stem) 463,800 36.76 314,269 42.62
 Madison River 9,000 0.71 8,333 1.13
 Yellowstone R.: West Rosebud Cr. 10,000 0.79 5,936 0.80
TOTAL, Missouri River Basin 482,800 38.26 328,538 44.55
TOTAL for State 1,261,830 100.00 737,454 100.00

 

The additional waterpower potential is estimated at nearly 18 billion kilowatt hours annually, or nearly three times the present production. Further investigation of potential power developments may be expected to result in reduction of potential because of unfavorable geologic conditions, incompatibility of interests, economic feasibility, and other causes. The data of table 10 were derived from information published by the Federal Power Commission except for the deletion of a, few projects now believed unfeasible. The table does not include the added power available through the reconstruction or improvement of present projects.

Table 10. Installed capacity and average annual power data for undeveloped power resources in Montana
STREAM
Undeveloped
installed
capacity
(kilowatts)
Percent of
State total
Undeveloped
average
power
(kilowatts)
Percent of
State total
Columbia River Basin:        
 Kootenai River (main stem) 1,180,000 24.16 374,772 18.37
    Yaak River 159,200 3.26 46,233 2.27
 Clark Fork (main stem) 480,000 9.83 173,402 8.50
    Rock Creek 51,500 1.05 23,002 1.13
    Blackfoot River Basin 146,300 3.00 48,208 2.36
    Flathead River Basin 1,044,800 21.39 307,191 15.06
    Thompson River 33,000 0.68 41,667 2.04
    Bull River 2,200 0.04 1,005 0.05
Total, Columbia River Basin 3,097,000 63.41 1,015,480 49.78
Missouri River Basin:        
 Missouri River (main stem) 310,500 6.36 210,160 10.31
    Jefferson River Basin 147,000 3.01 73,516 3.60
    Madison River 36,500 0.75 22,375 1.10
    Gallatin River 20,800 0.43 12,329 0.60
    Sun River 20,500 0.42 6,963 0.34
    Marias River 3,600 0.07 1,027 0.05
Total, Missouri above Yellowstone R. 538,900 11.04 326,370 16.00
 Yellowstone River (main stem) 920,000 18.84 536,530 26.30
    Mill Creek 15,000 0.31 7,991 0.39
    Boulder River 10,000 0.20 6,849 0.34
    Stillwater River 40,000 0.82 21,689 1.06
    Bighorn River Basin* 255,000 5.22 121,918 5.97
    Powder River 8,000 0.16 3,311 0.16
Total, Yellowstone River Basin 1,248,000 25.55 698,288 34.22
Total, Missouri River Basin 1,786,900 36.59 1,024,658 50.22
Total for State 4,883,900 100.00 2,040,138 100.00
*includes Yellowtail project now (1963) under construction with planned installed capacity of 200,000 kilowatts        

BASIN APPRAISALS OF WATER RESOURCES

The preceding discussion on the water resources of Montana presents a broad picture. Because interest is often directed to a specific locality, a somewhat more detailed discussion by river basins or subdivisions of major river basins follows.

COLUMBIA RIVER BASIN

Kootenai River.--The Kootenai River heads in Canada and flows through the extreme northwestern part of the State for a distance of 100 miles. The drainage area of about 4,000 square miles in Montana is mostly mountainous and heavily timbered. The main stream is well entrenched and has an average gradient of 5 feet per mile. The average unit runoff for the drainage in Montana is 11 inches and has a tendency to increase in a downstream direction. Nearly one-half the annual runoff occurs during May and June when rains generally augment runoff from mountain snowmelt. The recession during July and August is more gradual than the pattern illustrated in the hydrograph for the Flathead River near Columbia Falls (fig. 48). In the 51 years of discharge record for the Kootenai River at Libby, the annual discharge has varied from 57 to 138 percent of the average, a measure of high dependability. Some data regarding streams of the area are given below:

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Kootenai R. at Newgate, B.C., near entry into Montana 7,660.0 31 10,380 98,200 994 minor
Fisher River near Jennings, MT 780.0 10 567 6,320 60 minor
Granite Creek near Libby, MT 23.6 8 65 1,960 0* none
Kootenai River at Leonia, ID, near entry into ID 11,740.0 33 13,850 123,000 996 14,600
* Creek blocked by snowslide            

Ground water is available from unconsolidated deposits underlying the Kootenai River Valley and those of its principal tributaries. Wells yielding from 250 to 1,000 gallons per minute can be constructed in some parts of the drainage, notably in the valley of the Tobacco River near its mouth and in the Libby Creek Valley. Wells yielding over 1,000 gallons per minute are believed possible in the Kootenai Valley near the mouth of the Yaak River.

Little is known regarding the quality of the surface and ground water. The low turbidity of the water, geologic data, and current usage of surface and ground water indicate very favorable quality characteristics in all or most of the basin.

The utilization of water for irrigation is relatively minor and could be expected to vary greatly with the abundance of summer precipitation. Both surface and ground water are used for municipal purposes and the processing of lumber and minerals. Two hydroelectric power plants on Lake Creek near Troy have an installed capacity of 4,500 kilowatts. The considerable hydroelectric power potential of the main stream, and some tributaries, periodically has received active consideration. The recreation associated with the water resources is enjoyed by a sparse local population.

Clark Fork above Flathead River.--The Clark Pork above the mouth of the Flathead River drains about 10,800 square miles of west-central Montana west of the Continental Divide. The main stream and a number of the tributaries flow through large intermontane valleys. The precipitation generally increases in a downstream direction, and the effect is apparent in the flow of streams and in the varying density of timber stands. The undepleted annual runoff is equivalent to an average depth of about 10 inches over the watershed. The annual runoff of tributaries may vary from less than 5 inches to more than 25 inches. The melt of the winter accumulation of mountain snow results in a peakflow period in May and June. Rains during that period contribute greatly to the runoff. Water use for irrigation has an appreciable effect on the regimen of some streams and to a lesser extent on the total annual flow. A few of the available data on the streams are below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Middle Fork, Rock Cree, near Philipsburg, MT 123.0 24 119.0 1430 4.5 minor
Nevada Creek above reservoir near Finn 116.0 22 35.6 1800 2.0 2900
Clark Fork above Missoula 5999.0 32 2813.0 31,500 340* 120,000
Blodgett Creek near Corvallis 26.4 14 71.3 836 1.2 0
Clark Fork below Missoula 9003.0 32 5162.0 52,800 388.0 235,000
Clark Fork at Saint Regis 10,709 51 7376 68,900 1000.0 244,000
* Minimum daily            

The use of the water and effects of use indicate good to excellent natural water quality. The deterioration of water quality through irrigation is minor. The industrial use of water for the mining and smelting of ores at Butte and Anaconda occasionally results in slightly acid water in the upper reaches of the Clark Fork. The control measures near Anaconda have improved water quality to the point that trout are found on the main stream above the mouth of the Little Blackfoot River.

The unconsolidated deposits in the several large intermontane valleys of the Clark Fork and major tributaries contain large quantities of ground water. Wells yielding more than 1,000 gallons per minute can be constructed in many parts of the Missoula, Bitterroot, Deer Lodge, and Divide Creek Valleys. Smaller ground water supplies of from 250 to 1,000 gallons per minute are generally available in the upper Blackfoot River Valley and the valley of Flint and Blacktail Creeks. Some ground water development has been undertaken in parts of these valleys, but the supply is very large and the potential for additional development is great.

The principal use of water is for the irrigation of about 244,000 acres of land. Nearly one-half the acreage is in the broad valley of the Bitterroot River. Development of ground water for irrigation is of recent origin and serves only a small part of the irrigated acreage. The annual depletion of streamflow by irrigation is estimated to be about 300,000 acre-feet or 5.6 percent of the available supply. A hydroelectric power plant on the Clark Fork, downstream from the mouth of the Blackfoot River, has an installed capacity of 3,040 kilowatts. The industrial use of water for the processing of ore and the timber products is of considerable economic importance. The withdrawals for industrial use are principally from surface water sources as are those for municipal supply. The streams and lakes offer many opportunities for fishing, boating, and other water-based recreational uses.

Flathead River. The Flathead River drainage comprises an area of 9,077 square miles of which 450 square miles lie in Canada. Prominent intermontane valleys, formed by block faulting, are occupied by the main stream and its major tributaries and form an unusual drainage pattern. Flathead Lake, with a surface area of nearly 200 square miles, occupies a part of one of these valleys. The drainage is mostly timbered; but grasslands are common in the semiarid southwest part. The annual runoff for the upstream one-half of the drainage area is equivalent to a water depth of 29 inches, and that for the entire drainage is about 18 inches. The general runoff pattern is typical of those basins with heavy winter precipitation in the form of snow and relatively light summer precipitation. Tributary streams of the southwest part of the drainage show some characteristics of plains-type runoff. Summary data on the flow characteristics of a few streams are presented below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Flathead River at Flathead, B.C. 450 10 1002 14,600 65 none
Flathead River at Columbia Falls, MT 4464 33 9543 102,000 798 minor
Stillwater River near Whitefish, MT 325 20 340 4330 40 minor
Flathead River near Polson, MT 7096 54 11,610 82,800 32* 10,000
* Minimum daily            

Little is known of the ground-water potential of the large tributary valleys north of Flathead Lake. The supply is believed to be large, however, and wells of high yield could be developed locally. In the Flathead valley north of Flathead Lake, wells yielding more than 1,000 gallons per minute are possible and some development has taken place in the area. In the valleys of Ashley Creek, Little Bitterroot River, and Jocko River, wells yielding from 250 to 1,000 gallons per minute can be constructed locally.

Available information indicates water of excellent quality is present in most of the drainage area. In a few subareas, such as the Little Bitterroot River Basin, surface and shallow ground water supplies may be of poor quality.

The principal use of wafer is for the generation of hydroelectric power. The multiple-purpose Hungry Horse Reservoir on the South Fork Flathead River has a usable capacity of 3,428,000 acre-feet available for onsite power generation of 285,000 kilowatts and regulation for downstream hydroelectric power, flood control, and irrigation. The regulation of Flathead Lake through a range in stage of 10 feet provides 1,219,000 acre-feet of storage for the Kerr plant that has an installed capacity of 168,000 kilowatts. Power plants on Swan River and Big Creek have a combined capacity of 4,500 kilowatts. About 91,000 acres of land are irrigated, principally from tributary streams south of Flathead Lake. The annual depletion by irrigation has been estimated at 109,000 acre-feet, less than 1 percent of the supply. A number of reservoirs on small tributaries provide storage capacity of more than 150,009 acre-feet of wafer for irrigation. Ground and surface water are used for municipal supply. Water-based recreation plays an important part in the economy of the area.

Clark Fork from Flathead River to State line.--The Clark Fork drainage is relatively narrow through this region of 2,200 square miles. The crests of the Bitterroot and Cabinet Mountains form most of the boundary and intermontane valleys are small. In a number of reaches, the Clark Fork occupies a narrow bedrock channel parallel to a deeper filled channel of the ancestral Clark Fork. The stream gradient varies greatly but averages 4 feet per mile. The region is almost entirely timbered. The western part of the area has a high rate of precipitation, particularly in the Bitterroot Mountains. The gain in the discharge of the Clark Fork through this reach indicates an annual runoff equivalent of 11.6 inches. The runoff pattern is similar to that of the upstream areas described previously, although the main steam pattern is modified by regulation. The discharge records of a few streams are presented below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Clark Fork near Plains 19,958 51 19,570 134,000 3200 335,000
Thompson River near Thompson Falls, MT 642 5 502 4960 89 minor
Prospect Creek near Thompson Falls 182 5 266 2860 36 none
Clark Fork at Whitehorse Rapids near Cabinet, ID 22,067 33 21,450 153,000 969* 354,000
* Regulated minimum daily            

Large ground-water supplies are available in only a few areas because of the restriction of the Clark Fork Valley. Wells yielding from 250 to 1,000 gallons per minute can be constructed where the valley widens above Noxon Reservoir, but similar well yields are not known to be available elsewhere in the valley.

Surface and ground-water supplies of good quality are indicated by the geology and water utilization practices in the area.

Generation of hydroelectric power is the principal water use. The Thompson Falls hydroelectric plant with a capacity of 30,000 kilowatts, the Noxon plant with a capacity of 282,800 kilowatts and the Cabinet Gorge plant, located a mile downstream from the Montana boundary and with a capacity of 200,000 kilowatts, utilize three-fourths of the power head of the Clark Fork. These plants rely mainly upon the water stored by Hungry Horse and Kerr Dams. Approximately 15,000 acres of land are irrigated along the main stem and tributaries. Ground water is used to irrigate a few small tracts. Municipalities utilize surface water and rural residents depend on ground-water supplies. The artificial water bodies and streams offer recreational opportunities that are enjoyed by the local population and visitors.

MISSOURI RIVER BASIN

Tributaries above Three Forks.--The Jefferson, Madison, and Gallatin Rivers drain all of southwestern Montana east of the Continental Divide, an area of about 14,000 square miles. The name Missouri River is properly used below the confluence of the Jefferson and Madison Rivers, and the Gallatin River enters a few miles downstream. These principal streams and their tributaries flow through a number of large intermontane valleys.

The Jefferson River drains about 9,700 square miles and the main stem is known successively as the Red Rock River and Beaverhead River to the mouth of the Ruby River. The main stream and the principal tributaries, the Big Hole, Ruby, and Boulder Rivers, flow through large valleys along parts of their courses. Much of the area receives less than 12 inches of precipitation and grasslands predominate. A few tributary streams have an April snowmelt runoff peak, although a May-June snowmelt runoff peak is characteristic. The extensive use of surface water for irrigation greatly modifies the natural flow pattern. The annual runoff adjusted for consumptive use is equivalent to about 4 inches from the watershed.

The Madison River heads in the high plateaus of Yellowstone National Park and drains about 2,500 square miles. The stream passes through a number of broad valleys, and grasslands are prominent at lower elevations. The basic mountain-streamflow pattern is modified by the effects of springs and ground-water storage. These effects are accentuated by irrigation. The natural runoff is equivalent to a depth of about 10 inches over the watershed.

The Gallatin River originates in the northwest part of Yellowstone National Park, and it flows through intermontane valleys before it enters the broad Gallatin Valley near Bozeman. Extensive irrigation in the Gallatin Valley reduces the May-June snowmelt runoff peak, particularly in years of low flow and light summer precipitation. The runoff from this drainage basin of 1,800 square miles is about 9 inches after adjustment for irrigation use.

Some discharge data and a few related facts for a number of gaging stations in the drainage area are given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Red Rock River below Lima Res. near Monida 570 40 138 2500 0* 10,000
Beaverhead River at Blaine 3,619 26 390 3130 7.0 115,000
Ruby River near Twin Bridges 935 16 188 1500 1.8** 28,000
Big Hole River near Melrose 2476 38 1091 14,100 49 136,000
Jefferson River at Sappington 9277 32 2093 21,000 134 345,000
Madison River near West Yellowstone 420 46 471 2150 100 0
Madison River below Ennis Lake near McAllister 2186 23 1594 7750 210** 23,000
Gallatin River near Gallatin Gateway 825 36 755 8060 117 1400
Bridger Creek near Bozeman 62.5 16 32 902 0.9 1200
Gallatin River at Logan 1795 45 949 9840 130 110,000
* Regulated
**Minimum daily
           

The surface and ground water of the basin is a calcium bicarbonate type with a relatively low concentration of dissolved solids. A minor amount of sediment is transported by the streams.

The thick unconsolidated deposits of the large intermontane valleys contain large quantities of ground water in storage. Supplies exceeding 1,000 gallons per minute are available from wells in the Jefferson and lower Beaverhead Valleys and in the Blacktail Creek Valley. Wells yielding from 250 to 1,000 gallons per minute can be constructed in the Red Rock, Horse Prairie, Ruby, and Big Hole Valleys. Ground water supplies in excess of 1,000 gallons per minute are available in parts of the Madison Valley and in most of the Gallatin Valley.

The principal water use is for the irrigation of about 500,000 acres. The consumptive use for this purpose is about 20 percent of the supply. Storage of only 155,000 acre-feet of irrigation water makes much of the area dependent on currently available streamflow. Clark Canyon Reservoir, now (1963) under construction on the Beaverhead River near Dillon, will have a capacity of 261,000 acre-feet for the irrigation of 21,800 acres of new land and a supplemental irrigation supply for 28,000 acres. The use of ground water for irrigation has been started in a few scattered areas. Hebgen and Ennis Lakes on the Madison River provide 420,000 acre-feet of storage for hydroelectric power generation on the Missouri River. A power plant below Ennis Lake has an installed capacity of 9,000 kilowatts. Municipalities rely on both surface and ground water supplies. A diversion from the Big Hole River is an important part of the municipal and industrial water supply for Butte in the Clark Fork of Columbia River drainage. The use of water for recreation is significant in the Madison, Gallatin, and Big Hole River drainage areas.

Missouri River, Three Forks to Great Falls.--In most of the reach between, Three Forks and Great Falls, the Missouri River traverses a mountain area. It flows in a northerly direction through Townsend Valley, crosses the lower end of the Helena Valley and emerges from the mountains near the town of Cascade, flowing in a rather narrow valley. The tributary Smith River occupies a large intermontane valley in its upper reaches. The other major tributaries, the Dearborn and Sun Rivers, leave the steep Rocky Mountain front to traverse a region of foothills and high plains to enter the Missouri River. In the reach of 209 river-miles between Three Forks and Great Falls, the Missouri River has a fall of about 700 feet, the greatest amount in the upstream half of the reach. The incremental drainage area is 8,900 square miles, and the cumulative area to a point below the mouth at the Sun River is 22,900 square miles.

The runoff from the area is equivalent to a depth of 4.5 inches after adjustment for consumptive use. The principal contribution to streamflow in this reach is from the snowmelt runoff of May and June when precipitation is also the greatest. The natural streamflow pattern is greatly modified by regulation and irrigation use. During years of low flow, such as occurred in 1961, these modifications result in a rather uniform flow throughout the year. A few discharge data are given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Missouri River at Toston 14,669 26 5135 32,000 562 535,000
Prickly Pear Creek near Clancy 192 35 47.7 927 0.5 700
Missouri River below Holter Dam near Wolf Creek 17,149 16 5023 34,900 500 574,000
Dearborn River near Craig 325 16 216 7960 8 3,300
Smith River near Eden 1594 10 252 12,300 3.1 24,500
North Fork Sun River near Augusta 258 17 360 4840 27 0
Sun River near Vaughn 1854 27 713 17,900 20 110,000

The largest ground water supplies are found in the unconsolidated alluvium and terrace deposits adjacent to the Missouri River and the lower reach of the Sun River. Supplies of 250 to 1,000 gallons per minute are generally available from this source. High terrace gravels mantle consolidated rocks adjacent to the mountains and, where thick enough, yield adequate water for domestic and stock use.

In much of the reach from the mountains to Great Falls, the consolidated rocks of Paleozoic and Mesozoic age are the only source of ground water supplies. The rock formations that are believed to be reliable sources of ground water include the Two Medicine formation, the Virgelle sandstone, the Kootenai formation (cut bank sand), the Swift formation, and the Madison limestone. Few of the formations are present at all locations and some are deeply buried. Little is known concerning the well yields available from these rocks, but large yields are obtained from the Madison limestone in the Great Falls area.

The surface water is generally of a calcium bicarbonate type with a relatively low concentration of dissolved solids. The shallow ground water is probably of the same type but has a higher concentration of dissolved solids. The water in the deeper consolidated rocks may vary as to type and probably has a greater concentration of dissolved solids.

The water of the Missouri River and its tributaries is used for the irrigation of about 295,000 acres in this area. Reservoirs on tributary streams have an aggregate capacity of 190,000 acre-feet to provide storage for irrigation. Canyon Ferry Reservoir on the Missouri River near Helena, with a usable capacity of 2,043,000 acre-feet, provides water storage for onsite and downstream hydroelectric power generation, irrigation, municipal supply, and recreation. Additional storage of 144,000 acre-feet of water for hydroelectric power is available in Hauser and Holter Lakes on the Missouri River near Helena. Nearly half the power head of the Missouri River is utilized in plants that have an installed capacity of 105,000 kilowatts. Surface water of good quality is the principal source of water for the larger municipalities, and ground water is generally used for the smaller community and individual supplies. Surface water generally supplies industrial users. The area has many opportunities for water-based recreation of all types and lands bordering the artificial water bodies are becoming increasingly popular as summer and permanent homesites.

Missouri River, Great Falls to Fort Peck Dam.-The Missouri River drainage from Great Falls to Fort Peck Dam extends from the Continental Divide in northwest Montana through the high plains and isolated mountain ranges to the plains of eastern Montana. There are 380 miles in this reach, and the drainage area increases from 22,900 to 57,500 square miles. Falls and rapids in the upper 50 miles account for about 700 feet of fall in the river. The natural gradient for the remaining 330 miles ranges from about 3 feet to 1 foot per mile with an average of 1.7 feet per mile. The principal tributaries are the Marias and Teton Rivers from the west and north, the Judith River, Musselshell River, and Dry Creek from the south. The tributary streams from the north are short. The runoff from the mountain areas reaches its peak in the May-June period as the winter accumulation of snow is melted. The plains area generally has a brief snowmelt period in March or early April and subsequent runoff is the result of rains of high intensity or above-average duration. The blending of the two distinct runoff types is modified by regulation and irrigation use. The runoff from this area is highly variable and may average about 0.7 inch annually, after adjustment for consumptive use. Some information regarding the streamflow is given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Missouri River at Fort Benton 24,749 71 7539 140,000 627* 730,000
Two Medicine Creek near Browning 317 27 389 7950 4.4 10,000
Marias River near Shelby 3242 53 948 40,000 10 65,000
Teton River near Dutton 1308 7 143 1310 16 44,000
Judith River near Utica 328 42 50 1120 0 minor
Missouri River near Zortman 40,763 27 8404 137,000 1120 850,000
Musselshell River at Harlowton 1125 51 157 4530 0 37,000
Musselshell River at Mosby 7846 29 214 18,000 0 103,000
Dry Creek near Van Norman 2554 20 58 24,600 0 minor
Missouri River below Fort Peck Dam 57,556 18 9252** 51,000 0* 950,000
* Regulated mean daily
** Since operational level of Ft. Peck Reservoir was reached
           

The quality of the surface water in this part of the drainage area is generally good; the water is a calcium bicarbonate type with somewhat higher concentrations of dissolved solids. Exceptions are the Teton River downstream from Choteau, the Musselshell River downstream from Ryegate, and the Missouri River downstream from Virgelle.

The water downstream from these points is a sodium sulfate type with relatively high concentrations of dissolved solids. Sediment concentrations are generally low throughout the basin except in the lower reaches of the Musselshell where the stream traverses the Bearpaw shale which is easily eroded and carried in suspension. Return flow from irrigation has an appreciable bearing on the quality of water in parts of the area.

The geology and the occurrence of ground water in this large area are complex. Most of the area north of the Missouri River has been glaciated, and glacial drift mantles much of the surface. Outwash gravels and buried gravel-filled valleys may be present locally and are sources of small ground water supplies. The availability of ground water supplies within this vast area can best be described for smaller tributary basins.

The geology of much of the Teton and Marias River drainages is similar, and in much of the area ground water supplies are difficult to obtain. Alluvium and terrace deposits adjacent to these streams and high terrace gravels near the mountains may yield small to moderate supplies of ground water. In the western part of the area the sandstones of the Two Medicine formation and the Virgelle sandstone are believed to be reliable sources of small ground water supplies. In the central part of the drainage area, ground water supplies are difficult to obtain except with deep wells, and the quality of the water is not known. North of the Teton River the Virgelle sandstone, Claggett formation, and Judith River formation underlie the area, and sandstones in these formations are generally reliable sources of small ground water supplies.

The Judith River and its tributaries drain a large topographic and structural basin, the Judith Basin, that is surrounded by isolated mountains. Much of the upland area of the Judith Basin is mantled by high terrace gravels that yield ground water supplies adequate for stock and domestic use. The alluvium of the Judith River and its principal tributary, the Ross Fork, also yields small to moderately large water supplies to wells. The consolidated rocks underlying the Judith Basin are important sources of ground water. Most of the consolidated rocks are exposed on the flanks of the surrounding mountains and are thus favorably situated to receive recharge. The Kootenai formation ("Cat Creek sand"), Swift formation, Amsden formation, Kibbey formation, and Madison limestone are all sources of ground water, and most are used to some extent. These formations are deeply buried in most of the basin, but the contained water is under sufficient artesian pressure to cause many wells to flow at the land surface. Small to moderately large ground water supplies can be obtained from the consolidated rocks, and the Madison limestone, although not used at present, is believed to be a potential source of large water supplies. A number of large springs issue near the base of the mountains forming the east side of Judith Basin and are important locally as sources of water.

The Musselshell River and its tributaries drain a large area in central Montana, and ground wafer supplies are available from a number of sources. The alluvium and terrace deposits adjacent to the river yield from 250 to 1,000 gallons per minute to favorably located wells. In the headwaters region high terrace gravels cover an extensive area and, where adequately thick, yield small water supplies. The consolidated rocks are an important source of water, and ground water can be obtained from several formations. Where present, the Fort Union, Hell Creek, Fox Hills, Judith River, Claggett, and Eagle formations are water bearing and yield small to moderately large water supplies adequate for domestic and stock use. The Madison limestone, deeply buried in most of the basin, is a potential but unexplored source of large water supplies.

Fort Peck Reservoir, Montana, U.S.A. October 1994. Fort Peck Dam, one of the world’s largest earth-filled dams, and Fort Peck Reservoir are featured in this west-southwest-looking, low-oblique photograph. Fort Peck Dam was completed in 1940 as one in a series of dams built in the 1930s, 1940s, and 1950s along the upper watershed of the Missouri River. Besides providing flood control, hydroelectric power, irrigation water, and recreation facilities, the dam serves to impound water for later use from spring rains and snowmelt that swell the Missouri River. Fort Peck Reservoir is approximately 135 miles (217 kilometers) long and a maximum of 16 miles (26 kilometers) wide. The broad valley of the Milk River (upper right) served as the course of the Missouri River before ice age glaciers changed the river to its present course further south. The Milk River is shown joining the Missouri River that meanders eastward toward North Dakota. (NASA photo)
The water of tributaries in this reach is used for the irrigation of about 220,000 acres. The water from ephemeral streams is used extensively for flood irrigation and the quantity used is dependent on the availability of flow. The water storage capacity available for irrigation is about 250,000 acre-feet exclusive of the 1,313,000 acre-feet in Tiber Reservoir on the Marias River. At present, that reservoir is used for flood control and recreation as the planned irrigation use has not developed. The five hydroelectric power plants on the Missouri River in the upper reach have an installed capacity of 193,000 kilowatts. The power plants are dependent on upstream water storage. Fort Peck Reservoir, with a normally usable water supply of about 14 million acre-feet, provides storage for flood control and the generation of hydroelectric power. The installed capacity of the plant is 165,000 kilowatts. The recreational use of water in the various reservoirs is enjoyed by the local population. The mountain tributaries offer trout fishing.

Missouri River, Fort Peck Dam to State line.--Half of the Missouri River drainage area of 44,500 square miles between Fort Peck Dam and the border of North Dakota is in the Milk River drainage. A similarity of its many water-resource characteristics and those of the strip that extends along most of Montana's northern border allows a joint discussion of the two areas. In preglacial times the Missouri River occupied the present valley of the Milk River from near Havre to the mouth of the Milk. From this point the Missouri flows in its preglacial valley to the vicinity of Poplar, where it once flowed northeastward toward Hudson Bay. Thick beds of unconsolidated alluvium were deposited in the preglacial valleys. The Milk River heads in Glacier National Park and passes through a part of southern Canada before returning to the United States northwest of Havre. The principal northern tributaries of the Milk and Missouri Rivers head in Canada. A plains-type pattern of tributary runoff similar to that of the Poplar River prevails except for the few square miles in Glacier National Park. The melt of snow on the plains in early spring produces a high runoff rate. Precipitation from April to September is about 75 percent of the annual total, but little runoff results except from rains of high intensity or long duration that usually occur in June. The natural runoff of the Milk River drainage and the remainder of the area is approximately 0.5 inch as an annual average. The discharge data at a few representative points is given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Milk River at Milk River, Alberta 1036 45 310 8730 0 minor
Milk River at Nashua 22,332 22 695 45,300 0.6 140,000
Missouri River near Wolf Point 82,290 18* 10,010 46,800 680** 1,000,000
Redwater Creek at Circle 547 26 16.6 6730 0 minor
Poplar River near Poplar 3174 30 145 37,400 0 8000
*1943-61 after operational level of Ft. Peck Reservoir was reached
** Minimum daily
           

The surface water originating in the area has relatively high concentrations of dissolved solids and is a sodium bicarbonate type. The sediment yield of the tributary streams is high as the shales and sandstones of the area are easily eroded.

Wells tapping the alluvium in the preglacial valley of the Missouri River yield over 1,000 gallons per minute at many locations. High terrace gravels are present in northeastern Blaine County and wells yielding 1,000 gallons per minute can be constructed locally. However, the low recharge rate will limit the number of such wells. Downstream from the Poplar River the alluvial fill in the Missouri Valley is thinner and wells yielding from 250 to 1,000 gallons per minute can be constructed. Water from the alluvium in this area is highly mineralized, but is usable for some purposes. In much of the area remote from valleys, small ground water supplies adequate for domestic and stock-water use can be constructed in consolidated rocks. These rocks include the Judith River, Fort Union, and Bell Creek formations. Other water-bearing rocks are present at depth, but the water is thought to be brackish.

Only a small part of the irrigated land is supplied with water from the Missouri River. Most of the 160,000 acres of irrigated land lies near the Milk River and along its major tributaries in the United States and Canada. The transbasin diversion of water from the St. Mary River to the Milk River is about 150,000 acre-feet annually. The water of the Milk River and the tributary areas in Canada is subject to apportionment determined by an international treaty. The irrigation-water storage capacity is about 205,000 acre-feet in the Milk River drainage in the United States and about 110,000 acre-feet in Canada. The utilization of ground water for irrigation has shown a considerable increase in recent years. Lake Bowdoin and Medicine Lake refuges play an important part in the propagation and preservation of waterfowl.

Yellowstone River and tributaries. (Map at left from USGS.)--The Yellowstone River heads in the high mountains in Wyoming southeast of Yellowstone National Park and the principal tributaries have a high proportion of mountain drainage. The highest point in the State, Granite Peak of the Absaroka Range, lies in this drainage. The tributaries from the north are few and are generally short. There are about ]2,000 square miles in this drainage, of which 9,000 are in Montana and 3,000 in Wyoming. The unit runoff from the Absaroka Range is high but tends to decrease progressively downstream. The main stream and the principal tributaries have flow patterns typical of high mountain areas where the melt of winter snow provides most of the runoff. The runoff from the area is somewhat greater than that of any other similar-sized part of the Missouri River Basin in Montana, and is highly dependable. After adjustment for irrigation use, the runoff from the entire area is about 8 inches. The use of water for irrigation greatly modifies the natural flow pattern of the tributary Shields River, Sweetgrass and Pryor Creeks. Some data for representative sites are given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Yellowstone River at Corwin Springs 2623 55 3014 32,000 389 1000
Yellowstone River at Livingston 3551 36 3556 30,600 590* 24,000
Shields River at Clyde Park 543 32 152 4,500 1.8 19,500
Stillwater River near Absarokee 975 26 903 10,600 58 24,000
Clarks Fork Yellowstone River at Edgar 2032 40 1030 10,900 36 41,500
Yellowstone River at Billings 11,795 33 6409 64,800 430 350,000
* Minimum daily
           

Water in this part of the area is generally a calcium bicarbonate type with a relatively low concentration of dissolved solids and is suitable for most uses. Sediment concentrations also are low during most of the time.

Moderate to large ground water supplies are available from the alluvium and terrace deposits adjacent to the river. Wells yielding from 250 to 1,000 gallons per minute can be constructed at many locations in the valley, the most favorable sites being close to the river where the underlying gravels can be readily recharged. In parts of the area bordering the Yellowstone Valley, adequate ground water supplies are difficult to obtain. In areas remote from the valley, a number of consolidated rock formations yield water supplies adequate for stock and domestic needs and locally large supplies are available. North of the Yellowstone Valley, the Judith River, locally the Claggett, and the Eagle formations are sources of water supply. South of the Yellowstone Valley ground water supplies are difficult to obtain in much of the area, but adjacent to the Pryor Mountains large ground water supplies can be obtained locally. The Chugwater formation, Tensleep sandstone and Madison limestone are sources of large water supplies, and wells yielding artesian flows of several thousand gallons per minute can be constructed. Ground water obtained from the formations listed as sources of supply generally is much less suitable in quality for most uses than that of surface water supplies.

The principal use of the water in this part of Montana is for the irrigation of about 350,000 acres along the main stream and tributaries. Assuming an average consumptive use of 1.5 feet per acre, the depletion would be 530,000 acre-feet or about 11 percent of the available supply. The natural flow is supplemented by about 50,000 acre-feet of irrigation water storage which has only a minor effect on stream regimen. The high head Mystic Lake development on East Rosebud Creek has a power generating capacity of 10,000 kilowatts. Most of the population is served by municipal water supplies obtained from surface sources. The Yellowstone River compact applies to the apportionment of part of the water of Clarks Fork of Yellowstone River. The water of the area has a high recreational value for fishing, and hot springs in some areas have been developed as resorts.

The Bighorn River enters the Yellowstone River about 55 miles northeast of Billings to increase the drainage area from about 13,600 to 36,500 square miles. About 19,000 square miles of the Bighorn Basin lie in Wyoming where the drainage is chiefly mountainous, and the natural flow of the Bighorn River is greatly modified by extensive irrigation and storage for hydroelectric power generation. The area of nearly 4,000 square miles in Montana includes a small part of the Bighorn Mountains and extends through the foothills and high plains area. The valleys of the Bighorn and Little Bighorn Rivers in the State are large. The natural runoff in Montana is typical of a combination of mountain and plains runoff. The data given below are indicative of the runoff characteristics.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Bighorn River near St. Xavier, MT 19,626 27 3426 37,400 228 375,000
Little Bighorn RIver near Hardin 1294 8 181 3000 0.2 17,000
Bighorn River at Bighorn 22,885 16 3558 26,200 540* 465,000
* Minimum daily
           

The quality of the surface water is affected by extensive irrigation in Wyoming. The water entering Montana is a sodium sulfate type with a relatively high dissolved solids content. There is a slight dilution by tributary inflow in Montana. The sediment load of the Bighorn River as it enters the State is generally high.

Large ground water supplies are not generally available in this drainage. Supplies adequate for domestic and stock use can be obtained from the alluvium and locally from the high terrace gravels adjacent to the Bighorn and Little Bighorn Rivers. East of the Little Bighorn River small supplies of fair quality may be available where the Fort Union and Hell Creek formations are present.

The irrigation of about 3,000 acres of land in Montana is the principal use of the water. Storage of 23,000 acre-feet in the Lodgegrass Creek area supplies irrigation water for Indian lands in the Little Bighorn River Valley. Water for livestock is an important economic use. Yellowtail Dam currently (1963) is under construction on the Bighorn River where it leaves the mountains. The capacity of the reservoir will be 1,375,000 acre-feet; a large part of the storage area will be in Wyoming, A hydroelectric power plant with a capacity or 200,000 kilowatts is planned with provisions for irrigation, flood-control, and sediment storage.

The Yellowstone River drainage from the mouth of the Bighorn River to the State line includes most of the southeastern part of the State. The drainage area increases from about 36,500 to 69,000 square miles, one-third of the increase in area is in Wyoming. The drainage area is principally one of high plains. The main stream occupies a rather narrow central valley that occasionally widens to form broad lowlands. Snowmelt in the tributary drainage in March or early April results in runoff and the subsequent runoff peaks are caused by above average precipitation. Some of the tributaries head in the Bighorn Mountains of Wyoming and may show a peak from the May-June snowmelt. The high variability of streamflow from the tributaries affects the uniformity of flow of the main stream. The runoff equivalent of the area ranges from less than 0.5 inch to 1.5 inches after adjustment for consumptive use. Discharge data at a few representative points are given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Tongue River at Miles City 5739 18 341 12,000 0 90,000
Yellowstone River at Miles City 48,253 34 10,710 96,300 996 1,100,000
Powder River near Locate 13,189 23 570 31,000 0 52,000
Yellowstone River near Sidney 68,812 49 12,740 159,000 470 1,250,000

The water of the Yellowstone River and its tributaries is a sodium sulfate type with a relatively high dissolved-solids concentration. The sediment load of the Yellowstone River and its tributaries is relatively high.

Along the Yellowstone Valley and tributary valleys of the Tongue and Powder Rivers, ground water supplies of from 250 to 1,000 gallons per minute can be developed locally from the alluvium and terrace deposits adjacent to the streams. In areas remote from the streams, several consolidated formations yield adequate water for stock and domestic, municipal, and some industrial uses. The Fort Union, Hell Creek, and Fox Hills formations are the principal sources of water. At low elevations in the Yellowstone, Tongue, and Powder River Valleys, flowing artesian wells can be drilled in these formations. Along the crest of the Cedar Creek anticline in Fallon, Wibaux, and Dawson Counties, impermeable rocks are at the surface and ground water supplies are difficult to obtain.

There are about 180,000 acres of irrigated land in this reach, the greater part of which is along the Yellowstone River Valley. Flood irrigation is common along the smaller tributaries. The water of the Tongue and Powder Rivers is subject to allocation under the terms of the Yellowstone River compact. The surface and ground water used for livestock has a high economic value, and availability is often a limitation on range use. Municipal supplies are obtained from both surface and ground water. Water from the Yellowstone River is used in steam-electric power plants with a combined capacity of about 55.000 kilowatts,

LITTLE MISSOURI RIVER BASIN

An area of about 3,500 square miles in the southeast part of the State is in the Little Missouri River Basin. The River crosses the flank of the Black Hills uplift but the area is one of low relief. The soils are dominantly clays with low infiltration capacity, and impermeable rocks underlie most of the area. Precipitation from April to September constitutes about 75 percent of the annual total and, when sufficient, results in a good native grass cover. The runoff varies widely from year to year and averages about 1.5 inches. A March or April runoff peak is typical of the streamflow pattern. Summer rains may cause runoff peaks between extended periods of low flow. The storage of tributary flow for stock water and flood irrigation of hay meadows modifies streamflow patterns. A few representative runoff records are given below.

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Little Missouri River near Alzada, MT 904 41 79.8 6000* 0 minor
Little Beaver Creek near Marmarth, ND 615 23 39.7 12,700 0 minor
Beaver Creek at Wibaux, MT 351 23 24.2 3780** 0 150
* Maximum daily
**Peak of 30,000 cfs determined for flood of June 7, 1929
           

The supply of ground water is believed to be very limited in quantity because of the impermeable character of the soils and underlying rocks. The alluvium and terrace deposits of the principal streams may yield supplies adequate for domestic and stock use.

The quality of known surface and ground water supplies is generally poor. The streams of the basin traverse easily eroded shales and sandstone and as a result carry high concentrations of sediment.

The principal economic uses of the water supply are for stock and the occasional irrigation of hay or grasslands, as variable supplies permit. Ground water is the principal source for small municipal and domestic supplies.

 

SASKATCHEWAN RIVER BASIN

A small part of Montana east of the Continental Divide drains northward into the Saskatchewan River and thence to Hudson Bay. Most of this area of about 650 square miles is in Glacier National Park. The precipitation in the mountainous part is the highest in the State. A number of small glaciers in the area and the extremely heavy snowpack result in a prolonged high runoff period that extends well into July. The annual runoff of the three principal streams ranges from about 37 to 26 inches. The annual runoff of Grinnell Creek, as shown below, is equivalent to 97 inches of water. The lowest runoff is for the St. Mary River, which has a large part of its drainage in the foothills. The runoff data for a few streams are given below:

Stream
Drainage Area (sq mi)
Years of record
Avg. Discharge (cfs)
Maximum discharge (cfs)
Minimum discharge (cfs)
Irrigated land served (acres)
Belly River at international boundary 74.8 10 262 2450 12* none
Grinnell Creek near Many Glacier 3.47 12 24.9 242 0.2 none
St. Mary River at international boundary 469 44 705 40,000** 16* ***
* Minimum daily
**June 1908, prior to period of record
***Diversion to Milk River Basin equivalent to about 200 cfs
           

Because of abundant surface water supplies, ground water use is small. The prominent gravel terraces flanking the mountains might be expected to yield abundant water supplies of good quality. The surface water is a calcium bicarbonate type with a low concentration of dissolved solids. Sediment concentrations are also low.

The recreational use of the waters is high, as might be expected in a national park. The preservation of natural features in the park and the international boundary limit the extent of water use for other than recreational purposes. Sherburne Reservoir on Swiftcurrent Creek was created prior to the establishment of Glacier Park and has a storage capacity of 66,200 acre-feet of water for irrigation. The transbasin St. Mary Canal seasonally diverts an average of 150,000 acre-feet of water to the Milk River Basin. The water of the St. Mary River is apportioned between the United States and Canada in accordance with a treaty.

SELECTED REFERENCES

Culler, R. C., 1961, Hydrology of stock-water reservoirs in upper Cheyenne River basin: U.S. Geol. Survey Water-Supply Paper 1531-A, 136 p., 20 figs.

Ellis, A. J., and Meinzer, O. E., 1924, Ground water in Musselshell and Golden Valley Counties, Montana: U.S. Geol. Survey Water-Supply Paper 518, 92 p., 5 pls.

Federal Power Commission, 1960, Hydroelectric power resources of the United States.

Fisher, C. A., 1909, Geology and water resources of the Great Falls region, Montana: U.S. Geol. Survey Water-Supply Paper 221, 89 p., 7 pls.

Groff, S. L., 1958, A summary report on the ground-water situation in Montana: Montana Bur. Mines and Geology Inf. Circ. 26, 45 p., 7 pls.

Hackett, O. M., Visher, F. N., McMurtrey, R. G., and Steinhilber, W. L., 1960, Geology and ground-water resources of the Gallatin Valley, Gallatin County Montana, with a section on surface-water resources, by Frank Stermitz and F. C. Boner, and section on Chemical quality of the water, by R. A. Krieger: U.S. Geol. Survey Water-Supply Paper 1482, 282 p., 11 pls., 40 figs.

Hall, G. M., and Howard, C. S., 1929, Ground water in Yellowstone and Treasure Counties, Montana: U.S. Geol. Survey Water-Supply Paper 599, 118 p., 7 pls.

Hembree, C. H., Colby, B. R., Swenson, H. A., and Davis, J. R., 1952, Sedimentation and chemical quality of water in the Powder River drainage basin, Wyoming and Montana: U.S. Geol. Survey Circ. 170, 92 p., 44 figs.

Konizeski, R. L., McMurtrey, R. G., Brietkrietz, Alex, 1961, Preliminary report on the geology and ground water resources of the northern part of the Deer Lodge Valley, Montana: Montana Bur. Mines and Geology Bull. 21, 24 p., 1 pl., 7 figs.

--- 1962, Preliminary report on the geology and ground-water resources of the southern part of the Deer Lodge Valley, Montana: Montana Bur. Mines and Geology Bull. 31, 23 p., 2 pls., 8 figs.

Lohr, E. W., and Love, S. K., 1954, The industrial utility of public water supplies in the United States: U.S. Geol. Survey Water-Supply Paper 1300, Part 2, 462 p., 5 pls., 3 figs.

Lorenz, H. W., and Swenson, F. A., 1951, Geology and ground water resources of the Helena Valley, Montana, with a section on The chemical quality of the water by H. A. Swenson: U.S. Geol. Survey Circ. 83, 68 p., 4 pls., 11 figs.

Lorenz, H. W., and McMurtrey, R. G., 1956, Geology and occurrence of ground water in the Townsend Valley, Montana, with a section on Chemical quality of the ground water by H. A. Swenson: U.S. Geol. Survey Water-Supply Paper 1360-C, p. 171-290, pls. 19-20, figs. 29-40.

MacKichan, K. A., and Kammerer, J. C., 1960, Estimated use of water in the United States, 1960: U.S. Geol. Survey Circ. 456, 44 p., 10 figs.

McMurtrey, R. G., and Konizeski, R. L., 1956, Progress report on the geology and ground-water resources of the eastern part of the Bitterroot Valley, Montana: Montana Bur. Mines and Geology Inf. Circ. 16, 28 p., 2 pls., 5 figs.

McMurtrey, R. G., Konizeski, R. L., and Stermitz, Frank, 1959, Preliminary report on the geology and water resources of the Bitterroot Valley, 1Montana, with a section on Chemical quality of water by H. A. Swenson: Montana Bur. Mines and Geology Bull. 9, 45 p., 2 pls., 12 figs.

Meyers, J. S., 1962, Evaporation from the 17 Western States, with a section on Evaporation rates, by Tor J. Nordenson, U.S. Weather Bur.: U.S. Geol. Survey Prof. Paper 272-D, 100 p., 1 pl., 5 figs.

Moulder, E. A., and Kohout, F. A., 1958, Ground water factors affecting drainage in the First Division, Buffalo Rapids Irrigation Project, Prairie and Dawson Counties, Montana, with a section on Chemical quality of the water by E. R. Jochens: U.S. Geol. Survey Water-Supply Paper 1424, 198 p, 11 pls., 51 figs.

Moulder, E. A., Klug, M. F., Morris, D.A., and Swenson, F.A., 1960, Geology and ground-water resources of the lower Little Bighorn River Valley Big Horn County, Montana, with a section on Chemical quality of the ground water by R. A. Krieger: U.S. Geol. Survey Water-Supply Paper 1487, 223 p., 13 pls., 37 figs.

Perry, E. S., 1931, Ground water of eastern and central Montana: Montana Bur. Mines and Geology Mem. 2.

--- 1933, Possibilities of ground water supply for certain towns and cities of Montana: Montana Bur. Mines and Geology Misc. Contr. No. 2, 49 p., 2 pls., 70 figs.

--- 1934, Physiography and ground-water supply in the Big Hole Basin, Montana: Montana Bur. Mines and Geology Mem. 12.

--- 1934, Geology and artesian water resources along Missouri and Milk Rivers in northeastern Montana: Montana Bur. Mines and Geology Mem. 11, 34 p., 1 pl., 15 figs.

--- 1935 Geology and ground-water resources of southeastern Montana: Montana Bur. Mines and Geology Mem. 14.

Renick, B. C., 1929, Geology and ground-water resources of central and southern Rosebud County, Montana: U.S. Geol. Survey Water-Supply Paper 600, 140 p., 12 pls.

Simons, W. D., 1953, Irrigation and streamflow depletion in Columbia River basin above The Dalles, Oregon: U.S. Geol. Survey Water-Supply Paper 1220, 126 p., 1 pl., 1 fig.

Swenson, F. A., 1955, Geology and ground-water resources of the Missouri River valley in northeastern Montana, with a section on the quality of the ground water by W. H. Durum: U.S. Geol. Survey Water-Supply Paper 1263, 128 p., 1 pl., 18 figs.

--- 1957 Geology and ground-water resources of the Lower Marias irrigation project, Montana, with a section on Chemical quality of the ground water by H. A. Swenson: U.S. Geol. Survey Water-Supply Paper 1460-b, pp. 41-98, pls. 2-4, figs. 1-6.

Swenson, H. A., 1953, Geochemical relationship of water in the Powder River Basin, Wyoming and Montana: Transactions, American Geophysical Union, Vol. 34, June, 1953, pp. 443-448.

Thomas, N. O., Harbeck, G. E., 1956, Reservoirs in the United States: U.S. Geol. Survey Water-Supply Paper 1360-A, 99 p. 1 pl., 3 figs.

Torrey, A. E., and Swenson, F. A., 1951, Ground-water resources of the lower Yellowstone River valley between Miles City and Glendive, Montana, with a section on The chemical quality of the water by H. A. Swenson: U.S. Geol. Survey Circ. 93, 72 p., 1 pl., 12 figs.

Torrey, A. E., and Kohout, F. A., 1956, Geology and ground-water resources of the lower Yellowstone River valley between Glendive and Sidney, Montana, with a section on Chemical quality of the water by B. A. Swenson: U.S. Geol. Survey Water-Supply Paper 1355, 92 p., 2 pls., 14 figs.

U.S. Geological Survey, 1914, Profile surveys in the basin of Clark Fork of Columbia River, Mont.-Idaho-Wash.: U.S. Geol. Survey Water-Supply Paper 346, 6 p., 3 pls.

------ 1914, Profile surveys of Missouri River from Great Falls to Three Forks, Mont.: U.S. Geol. Water-Supply Paper 367 8 p., 1 pl.

------ 1949, Floods of May-June 1948 in Columbia River basin, with a section on Magnitude and frequency of floods by Rantz, S. E., and Riggs, H. C.: Water-Supply Paper 1080, 476 p., 12 pls.

--- 1955, Floods of April 1952 in the Missouri River basin: Water-Supply Paper 1260-B, pp. 44-302, pls. 24, figs. 11-35.

--- 1957, Floods of May-June 1953 in Missouri River basin in Montana: Water-Supply Paper 1320-B, pp. 69-153, pls. 3, 4, figs. 13-23.

Zimmerman, Everett A., 1956 Preliminary report on the geology and groundwater resources of parts of Musselshell and Golden Valley Counties, Montana: Montana Bur. Mines and Geology Inf. Circ. 15, 13 p., 1 pl., 2 figs.

--- 1960, Preliminary report on the geology and ground-water resources of northern Blaine County, Montana: Montana Bur. Mines and Geology Bull. 19, 19 p., 1 pl., 5 figs.

---- 1962, Preliminary report on the geology and ground water resources of southern Judith Basin, Montana: Montana Bur. Mines and Geology Bull. 32, 23 p., 1 pl., 4 figs.