Changes in Flow in the Upper North Canadian River Basin of Western

Changes in flow in the upper North Canadian

River basin of western Oklahoma, pre-development to 2000

K.L. Wahl

US. Geological Survey, Lakewood, Colorado, USA

Abstract

Water levels have declined in the southern part of the High Plains aquifer of the central USA since the mid-1960s in response to extensive irrigation development. The North Canadian River originates in western Oklahoma, and most of the basin is underlain by the High Plains aquifer. Average river flow in the headwaters near Guymon, Oklahoma, has decreased fiom about 0.9 m3/s before 1970 to near zero at present. Canton Lake, on the North Canadian River near Seiling, about 250 km downstream from Guymon, is a source of water supply for Oklahoma City. Precipitation data and streamflow data for gages upstream from Canton Lake were divided into an "early" period ending in 1971 and a "recent" period that begins in 1978. The early period represents conditions before ground-water levels had declined appreciably in the High Plains aquifer, and the recent period reflects the current condition, including the effects of storage reservoirs. Tests for trend and comparisons of flows between the early and recent periods show that the total annual volume of flow and the magnitudes of instantaneous annual peak discharges measured at most locations in the North Canadian River basin have decreased. Precipitation records for the area, however, show no corresponding changes. The decreases in average annual flow, expressed as a percentage of the average flows for the early period, ranged from

91 percent near Guymon to 37 percent near Canton Lake. A major contributing factor in the decreased flows appears to be the large declines in water levels in the High Plains aquifer.

1 Introduction

Optima Lake on the Beaver River near Guymon, Fort Supply Lake on Wolf

Creek near Fort Supply, and Canton Lake on the North Canadian River near Canton (fig. 1) provide storage of public-water supplies for western Oklahoma

River Basin Management 75

and for the Oklahoma City metropolitan area. The Beaver fiver and Wolf Creek join to form the North Canahan Rwer, which flows into Canton Lake. The drainage area at Canton Lake is 32,318 km2 and includes most of northwest Oklahoma (54 percent), along with a small part of northeastern New Mexico (6 percent), and the northern part of the Texas panhandle (40 percent). The principal industry in the basin is agriculture, with the land area about evenly divided between cropland and rangeland. Average annual precipitation in the study area ranges from about 400 mm in the west to 610 mm near Canton Lake in the east. The majority of precipitation occurs from spring through summer. Annual runoff to Canton Lake averages about 10 mm. Most runoff occurs between April and August, and the smallest streamflows usually occur from December through February. More than 90 percent of the Beaver-North Canadmn basin above Canton Lake is underlain by the High Plains aquifer, which underlies an area of about

450,500 km2 in eight States [l]. The High Plains aquifer is primarily a water-table aquifer recharged by precipitation. The estimated recharge rate for the High Plains aquifer in the Beaver River basin upstream from Guymon is 1.4 mm per year [2];this represents less than 1 percent of the mean annual precipitation. Prior to the start of large-scale pumping for irrigation in the 19601s,the aquifer was in equilibrium [3]. The introduction of the center-pivot sprinkler system in the early 1960's resulted in a rapid increase in the use of ground water for irrigation and consequent declines in ground-water levels (fig. 2). Long-term water-level monitoring for the High Plains aquifer indicates declines averaging 7.6 mm per year from 1940 to 1980 [4]; however, most of the change occurred after 1970. Water levels continued to decline from 1980 to 1993, but at a lower rate, averaging 4.9 mm per year. Local deches were greater; maximum declines in northern Texas and western Oklahoma were as much as 15 to 30 a The decline in ground-water levels, in combination with changes in land-use practices, has been recognized as a primary cause of decreases in the discharge of the Beaver- North Canalan River in Oklahoma 14, 5,6].

2 Background and methods of analysis

The U.S. Geological Survey has collected streamflow data in the study area since about 1937. Wahl and Wahl [6] used those data for all gages in the basin upstream from Beaver, Oklahoma, to defme changes in the flow regime. The average flow of the river near Guymon was about 0.9 m3 before 1970, but began to deche in the early 1970's. When I .e gage at Guymon was discontinued in 1993, the channel was dry more than 90 percent of the time (fig. 3), and the average annual flow for the past 10 years was near zero. Wahl and Tortorelli [7] examined flow changes upstream from Canton Lake using data for the 25 gages in the basin with at least 10 years of data. Base flows were estimated from daily mean discharge using a FORTRAN program, BFI, developed by Wahl and Wahl [6, 81. The program defines the Base Flow Index as the ratio of base flow to total flow.

2,500 .,,,,m,.,,,,,l,,l~..,l,,,,l,,,. 5BW U y 2,000 1 W 3 1,500 1 - W ELLS 8 -,-m-., 8 1,000 m €

2 500

0 ""'"" II,I,I, 1930 1940 1950 1980 1970 1980 1990 2000

YEAR

Figure 2: Growth in numbers of large-capacity wells in western Oklahoma, and decline in water levels in observation well 363033 101440701.

Figure 3: Annual percent of no-flow days for the Beaver River near Guymon, Oklahoma.

A non-parametric test was used to test for the presence of trends. Trend tests were limited to data collected after 1942 for sites downstream from Fort Supply Lake, which began storing water in 1942. Optima Lake was completed and began storing water in 1978, but storage in Optima Lake has been minimal. Moving averages of the data were also used to damp the fluctuations so trends were more readily apparent to the eye. Finally, data were divided into an "early" period ending in 1971, representing conditions before ground-water levels had declined appreciably and the "recent" period beginning in 1978, reflecting the condition of declining ground-water levels and the effects of storage reservoirs. Medians and averages of precipitation and streamflow for the "early" and "recent" periods were compared. Precipitation data collected at the Goodwell Research Station near Guymon between 1936-1986 were tested by Wahl and Wahl [6]. In addition,

River Basin Management 77

monthly and annual averages of precipitation for 1895-1994 for the climate division that covers western Oklahoma were tested by Wahl and Tortorelli [7].

The Guymon gage (07232500) is not affected by reservoirs, but the other three mainstem gaging stations are. The amount of annual change in storage in the upstream reservoirs is small in relation to the annual volume of flow. However, annual volumes were adjusted for change in reservoir contents. The medians of the adjusted and unadjusted annual volumes of flow differed by about 2 percent at the Beaver (07234000) and Seiling (07238000) gages, and by about 9 percent at the Woodward gage (07237500). The last year of record used in the adjusted record was 1993 because change-of-contents data for the lakes are not available for the 1994 water year.

3 Results

Comparisons of flows for the early period (ending in 1971) with those for the recent period (1978-1994) show that the magnitudes of peak discharges and the total annual volume of flow measured at most gaging stations in the Beaver-North Canadian Rwer basin have decreased in recent years. These changes are most pronounced in the headwaters upstream fiom Woodward, but also are evident at

Woodward and near Seiling, whlch represents the inflow to Canton Lake. The melans of the annual peak discharges decreased fiom the early period to the recent period by the following percentages: near Guymon (98), at Beaver (86), at Woodward (80), and near Sehg(53).

The year-to-year variation of precipitation over the area is large, but no discernible long-term trends were found, and differences between the "early" and "recent" periods were negligible [7]. Analyses of annual streamflow, however, show that the flows measured at most gaging stations in the Beaver-North Canadian River basin are smaller in the recent period. These results are summarized in Table 1 for the four main-stem Beaver-North Canadian River gages. Changes in annual peak discharges, annual volume of flows, and base flow index are shown in figures 4 and 5 for the gages near Guymon (07232500) and Selling (07238000). These gages represent the respective inflows to Optima Lake and Canton Lake.

Annual rates and volumes of flow have deched at most gaging stations in the basin [6, 71. The average daily rate of flow of the river near Guymon reported in 1960 for 23 years of record (water years 1938-1960) was 0.91 m3/s; the 10-year moving average was only 0.02 m3/s by 1993. The decrease in annual volume of flow near Guymon between the early period and the recent period was about 22,600 dam3 (cubic dekameters), which was 91 percent of the average for the early period. Even larger decreases were found in the annual flow volumes between the early and recent periods at Beaver (84,200 dam3), at Woodward (88,000 dam3),and near Seiling (78,000 dam3). Base flows also have undergone substantial change, but unlike the annual volumes the base flows show some decreases and some increases. The recent periods had large decreases at the Beaver River near Guymon and at Beaver. The average base flow near Guymon for 1978-1993 was only 10 percent

of that for the early period; and those results may understate the decrease. When

the gage near Guymon was discontinued in 1993, there was no base flow passing the gage. The average base flow at Beaver for the recent period is only 34 percent of that for the early period. In contrast, the average annual base flows at Woodward and near Seiling show little change between the early and recent period, but the median annual base flows have increased by about 45 percent in

the recent period. This change indicates a shift in the sources of annual flows. Large floods contributed substantially more to the annual average flows in the early period than in the recent period.

: Table 1 Summary of comparisons between early and recent period values for selected flow variables. [Units of peak values are m3/s; units of annual volumes and base flow are cubic dekameters (dam3),which are thousands of m3].

Early period Recent period Change Before 1972 After 1977 (early-recent) variable I I I r median mean median mean median mean

07232500 Beaver River near Guymon, 1938-93; Drainage = 5,538 km2

annual peak 140 28 -1 12 annual volume 102,000 180,000 92,600 91,000 -9,900 -88,000 base flow 34,300 53,900 50,000 53,400 15,700 -500

07238000 N. Canadian River near Seiling, 1947-94; Drainage area = 3 1,744 km2

annual peak 1 14 54 -60 annual volume 130,000 2 1 1,000 144,000 133,000 149000 -78,000 Baseflow 76,500 42,900 74,700 61,700 18,800 1,800

The decreases in flow upstream from Guymon have impacted Optima Lake, which was completed on the Beaver River near Guymon in 1978. The construction period (1966-78) coincided with the period of greatest decline in

flows. As a result, storage in Optima Lake has never exceeded 5-percent of capacity.

Ri~vrBasin Management 79

l-W 1W 1W 19W 1970 1SBL) 1993 ZOM WATER YEAR

Figure 4: Histograms and l0-year moving averages of A) annual peak discharge

(m3/s), B) annual volume of flow (dam3), and C) base-flow index for station 07232500 Beaver River near Guymon, Oklahoma.

A primary mechanism producing these decreased streamilows appears to be the depletion of ground water in the High Plains aquifer that underlies more in than 90 percent of the basin. Relations between decreases base flow and daily mean flows and ground-water level declines are easy to understand. The hk between declines in ground-water levels and annual peak discharges is not so clear, but the possible effect of a dry channel on attenuation of peak discharges cannot be discounted. Changes in farming and conservation practices also may be having an effect on the magnitudes of annual peak discharges. Flow duration analyses show that although the magnitudes of base flows have increased near Seiling, the magnitudes of the large flows that occur less than about 20 percent of the time were greatly reduced in the recent period. Those large flows occur infrequently, but contribute substantial amounts of the total annual volume of flow.

1940 1950 19m 1970 1m 19w mm WATER YEAR

Figure 5: Histograms and 10-year moving averages of A) annual peak discharge

(m3/s),B) annual volume of flow (dam3), and C) base-flow index for station 07238000 North Canadian River near Seihg, Oklahoma.

The reasons for the increase in median base flows at Woodward and near Seiling are not known. Possible contributing factors may include: 1) The

influence of discharge fiom the alluvium and terrace aquifer that is present in this reach of the river; 2) changes in discharge of wastewater; and 3) the effects of reservoir operations. Reservoirs commonly modulate flows - reducing the largest flows and increasing the smallest flows. The gaging records, however, suggest that the reservoirs are not primary factors in this change.

References

[l] Weeks, J.B., Gutentag, E.D., Heirnes, F.J., and Luckey, R.R., Summary of the High Plains Regional Aquifer-system analysis in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Professional Paper 1400-A, 30 p., 1988. [2] Luckey, R.R., E.D. Gutentag, F.J. Heimes, and J.B. Weeks, Digital Simulation

of Ground-Water Flow in the High Plains Aquifer in Parts of Colorado,

River Basin Management 8 1

Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming: U.S. Geological Survey Professional Paper 1400-D, 57 p., 1986.

[3] Havens, J.S., and S.C. Christenson, Numerical Simulation of the High Plains Regzonal Aquifer, Northwestern Oklahoma: U.S. Geological Survey Water- Resources Investigations Report 83-4269,27 p., 1984. [4]Dugan, .T.T. and Cox, D.A., Water-level changes in the High Plains Aquifer-

Predevelopment to 1993: U.S. Geological Survey Water-Resources Investigations Report 94-41 57,60 p., 1994. [5] Boyle Engineering Corporation, Northwest and Western Oklahoma Hydrologic Study - Rainfall/RunofAnalysis: Boyle Engineering Corporation,

Lakewood, Colorado, 117 p., 1987 [6]Wahl, K.L., and Wahl, T.L., Effects of regional ground-water level declines on streamflow in the Oklahoma Panhandle. Proceedings of Symposium on Water-Use Data for Water Resources Management, American Water Resources Association, August 1988, Tucson, Arizona, p. 239-249, 1988.

[7] WahL, K.L., and Tortorelli, R.L., Changes in flow in the Beaver-North Canadian River Basin upstream from Canton Lake, Western Oklahoma: US. Geological Survey Water-Resources Investigations Report 96-4304, 58 p., 1996.

[8]Wahl, K.L., and Wahl, T.L., Determining the flow of Coma1 Springs at New Braunfels, Texas. Proceedings of Texas Water195,A Component Conference of the First International Conference on Water Resources Engineering, American Society of Civil Engineers, August 16-17, 1995, San Antonio, Texas, p.77-86, 1995.