Bul 249–Ground-water Recharge and Water Budgets–––pages 56 to 65
Part II C and D
C13. Water Budgets for the Major Kansas Wetlands of Cheyenne Bottoms and Quivira National Wildlife Refuge
The two major Kansas wetlands of Cheyenne Bottoms and Quivira National Wildlife Refuge are shown in figs. II–10 and II–13. Sophocleous and Shapiro (1987) employed the Versatile Soil-moisture Budget (VB) model of Baier et al. (1979) to calculate the water budget of the nonwater-covered area of the Drummond–Tabler soil association (more than 86% of total area of approximately 60 mi2), which encompasses the Cheyenne Bottoms. The water budget was run for two water years (Oct. 1, 1982–Sept. 30, 1984). The vegetation cover of this area consisted of 44% small grains, 40% grasses, and 12% cattails. The average hydrologic budget for that area is shown in table II–21 with an estimated deep drainage of 2 inches/yr. This deep-drainage value is practically equal to ground-water recharge because of the shallow water table in the area.
TABLE II–21—Predevelopment (pre-1960) and present-day (1991–94) annual water budgets for the Rattlesnake Creek basin (values in inches/yr).
TABLE II–22—Average 1983 and 1984 water-year budget for the Drummond–Tabler soil association encompassing the Cheyenne Bottoms.
TABLE II–23—1985–1992 hydrologic budget components for Quivira National Wildlife Refuge (based on Hudson NOAA climatic station).
Note that the deep drainage is highly variable (high coefficient of variation) and is practically equal to ground-water recharge because of the relatively shallow depth to water table in the Quivira NWR.
C14. Equus Beds Aquifer Modeling
a) Green and Pogge (Green et al., 1973) Study
Green and Pogge (Green et al., 1973; see also Knapp et al; 1975) developed a comprehensive basin hydrology simulator by combining the Kansas Water Budget Model (Smith and Lumb, 1966), a model similar to the Stanford Watershed Model, with a two-dimensional finite difference ground-water model. They field-tested this simulator on the Little Arkansas River basin that encompasses the Equus Beds aquifer for the 1946–1970 period. Ground-water recharge data are only presented for subbasin 5 (within the drainage basin of Little Arkansas River), which includes 139 mi2 in portions of townships 23 S. to 25 S. and ranges 1 W. to 2 W., including the towns of Halstead and Sedgwick, Kansas.
FIGURE II–11—Percent of annual precipitation for the period 1946–1970 falling on subbasin 5 within the drainage basin of Little Arkansas River (encompassing Halstead and Sedgwick, Kansas) that percolates to ground water (adapted from Green et al., 1973).
FIGURE II–12—Simulated predevelopment (1940) recharge distribution in the Equus Beds aquifer, Kansas (adapted from Spinazola et al., 1985).
TABLE II–24—Simulated water budget for the Equus Beds aquifer (values in inches/yr).
d) Myers et al. (1996) Study
Myers et al. (1996) also employed the three-dimensional USGS MODFLOW model to study interactions between the Arkansas River and the Equus Beds aquifer in parts of Reno, Harvey, and Sedgwick counties, an area of approximately 690 mi2, that includes the cites of Hutchinson, Newton, and Wichita. The model area was divided into three layers, and was calibrated for both steady-state (pre-1940) and transient conditions (1940–1989). A variable-spacing model grid was laid out with rows parallel to the Arkansas River, with a smaller grid spacing (1,000 ft x 5,000 ft) near the river. The same recharge distribution developed by Spinazola et al. (1985) for 1940 was assumed valid for the steady-state pre-1940 model (representing 1934–39 conditions). The mean absolute difference between measured hydraulic heads for 235 individual wells and their corresponding middle-layer simulated hydraulic heads was 3.20 ft.
The transient model used the same five stress period as the ones used by Spinazola et al. (1985) plus a sixth stress period (1980–89), characterized by marked fluctuations in the volume of agricultural pumpage. Recharge was based on the mean precipitation at climatic stations at Hutchinson, Mount Hope, and Wichita for each stress period, and was estimated as follows (Myers et al., 1996): 1) the recharge specified for each steady-state model cell was divided by the mean annual precipitation for the pre-1940 period represented in the steady-state model; 2) the resulting quotient for each model cell was then multiplied by the study-area mean annual precipitation for each stress period in the transient model. The mean absolute difference between hydraulic heads for 232 individual wells and their corresponding middle-layer model cell at the end of 1989 was 4.67 ft. Streamflow that was exceeded 70% of the time at each gaging station, assumed to represent baseflow, was compared to model-simulated flow in the stream reach where the gaging station was located. Because streamflows specified for the starting stream reach in the model were held constant for each stress period, the model did not simulate the annual seasonal or short-term variation of measured streamflow (Myers et al., 1996).
The simulated steady-state and transient ground-water budgets for the periods 1964–1970, 1971–79, and 1980–89 are shown in table II–25.
TABLE II–25—Simulated steady-state and transient ground-water budgets for all three model layers of the Equus Beds aquifer (values in inches/yr).
C15. Other County-scale Recharge Studies
a) Grant and Stanton Counties, Southwest Kansas
Fader et al. (1964) estimated recharge from precipitation from a 1939–1942 water-level contour map of Grant and Stanton counties, assuming negligible well pumpage at that time period. By carefully selecting a study area of 160 square miles between the towns of Johnson and Ulysses, where it could be assumed that leakage inflow from the underlying sandstone aquifers was negligible, they estimated the recharge rate to be about 0.3 inch/yr, which is about 2% of the annual precipitation. This recharge rate was applied to the rest of the Grant and Stanton unconsolidated aquifers in their study. Fader et al. (1964) also estimated the recharge of the unconsolidated aquifers in the area from upward leakage from the underlying sandstone aquifers to be of approximately the same magnitude as the precipitation recharge.
b) Seward County
Byrne and McLaughlin (1948) estimated recharge from precipitation in Seward County based on 1941–44 well hydrograph data from three upland wells that showed an average rise of 0.22 ft/yr and assuming an aquifer specific yield of 0.15 to come up with a recharge estimate of about 0.4 inch/yr.
Frye (1942) made an inventory of water discharged from the artesian water-bearing beds of Meade County by upward leakage through the confining beds, along faults, through springs and flowing and nonflowing wells, and determined that the total annual discharge of artesian water was about 10,000 acre-feet. He concluded that nearly all the recharge to the artesian water-bearing beds occurs to the west and north of the county in southwestern Gray County, parts of Haskell County, northeastern Seward County, and the southernmost part of Finney County, an area of approximately 685 square miles. Assuming equilibrium conditions, where the recharge is assumed to be equal to the discharge, Frye (1942) estimated an average recharge of about 0.27 inch/yr, which represents about 1.5% of average annual precipitation in the area (considered as 18 inches/yr). According to Frye (1942), in the area of sand dunes in southern Finney County and northern Haskell County that percentage is probably much greater, and in certain other parts of the area it is probably much less, and locally there may be none at all.
d) McPherson Moratorium Area, Equus Beds Aquifer
McElwee et al. (1979) conducted a water-budget analysis of the McPherson moratorium area (56 mi2) of the Equus Beds aquifer based on January 1978 water-table levels. Recharge was estimated as 2 inches/yr (table II–26).
TABLE II–26—1978 water-budget analysis of the McPherson moratorium area, Equus Beds aquifer.
D. Field-based Experimental Recharge Studies
Field-experimental ground-water recharge studies in Kansas are highlighted in this section.
Prill (1968, 1977) conducted a study to investigate the requirements necessary for deep percolation under three types of vegetative conditions: 1) a barren area, 2) a sagebrush-grass community, and 3) a grass community, over a period from the fall of 1964 through 1966. This period depicts maximum moisture changes because 1965 was a year when precipitation was one of the highest on record (29.07 inches in Garden City) and was preceded and succeeded by years when precipitation was below normal (12.23 inches in 1964 and 12.04 inches in 1966).
The study site is located in the extensive area of dune sand immediately south of the Arkansas River near Garden City in southwestern Kansas. At each site, neutron probe access holes containing 2-inch aluminum tubing for moisture-content logging were drilled through the dune sand into the underlying alluvial deposits. The water table in this area was about 30 ft below the top of the alluvial deposits.
Even though the period of study included a year when precipitation was nearly the highest on record, built-up moisture under a sagebrush-grass community penetrated to a depth of only 14 ft, whereas the zone of evapotranspiration extended to at least 17 ft (Prill, 1968). Under a grass community where the zone of evapotranspiration extended to about 11 ft only a small amount of moisture (2 inches) moved as deep percolation. Under a barren area, where most of the loss by evaporation occurred in the upper 1 ft, large quantities of moisture moved as deep percolation.
D2. Pilot Recharge Assessment at Two Sites in South-central Kansas (Great Bend Prairie and Equus Beds Aquifers) (Sophocleous and Perry, 1985)
Sophocleous and Perry (1984, 1985, 1987) experimentally assessed ground-water recharge at two instrumented sites in south-central Kansas (one site near Zenith in Reno County (GMD5), and one near Burrton in Harvey County (GMD2) over an approximately 19-month period during 1982 and 1983. Although the two instrumented sites were located in sand-dune environments in areas characterized by shallow water table and subhumid continental climate, a significant difference was observed in the estimated effective recharge. The estimates ranged from less than 0.1 inch at the Zenith site to approximately 6.1 inches at the Burrton site during the major recharge period from February to June 1983. The main reasons for this large difference in recharge estimates were the greater thickness of the unsaturated zone and the lower moisture content in that zone resulting from lower precipitation and higher potential evapotranspiration for the Zenith site. Effective recharge took place only during late winter and spring. No summer or fall recharge was observed at either site during the observation period of this study.
Recharge-related variables were monitored in the field on a year-round basis at 10 sites distributed throughout the GMD5 area (fig. II–13; Sophocleous, 1991, 1992, 1993a, 1993b, Sophocleous and Stern, 1993). The methodology used in quantifying recharge for the region consisted of combining the hydrologic or soil-water balance on a storm-by-storm year-round basis with the resulting water-table rises. Each recharge-assessment site was equipped with a weighing and recording rain gage, a neutron-probe access tube for measuring the soil-profile water content, a water-table well with a water-level recorder, and two deeper piezometers. Two of the sites also were equipped with weather stations that recorded solar radiation, air temperature, relative humidity, barometric pressure, and wind speed. Using the data collected at these sites and detailed weather data from the Sandyland Experiment Station, just south of St. John (fig. II–13), the soil-water balance for each recharge-producing storm period was calculated. By associating the result with the consequent water-table rise, which was tied to specific precipitation events, reliable effective recharge values for different storm periods were obtained (Sophocleous, 1991).
FIGURE II–13—Groundwater Management District No. 5 boundary (heavy gray line) with ground-water recharge assessment sites (triangles). River basins are outlined with black lines.
Table II–27 gives the average values of measured precipitation, depth to water table, and estimated annual recharge for all the monitored sites in GMD5. For the original recharge sites 1 through 5, data have been collected from 1985 to 1992, whereas for sites 6 through 10 data were collected during the 1988–1992 period. The unusually high recharge estimates for site 4 in Reno County, which received the highest precipitation among all sites, were due to the site being located on the streambank of a tributary to Wolf Creek where the depth to the water table is very shallow, approximately 2–4 ft. Sites 8, 9, and 10 received no detectable recharge during the period 1988–1992.
TABLE II–27—1985–1992 site-specific ground-water recharge estimates for GMD5.
During the flood year of 1993, average precipitation in Stafford County was approximately 36.6 inches (which is approximately double the long-term average) and estimated average recharge (based on sites 1, 2, 3, and 5) was 5.9 inches. This amount of estimated recharge caused an average county-wide water-table rise of 5.4 ft (Sophocleous et al., 1996).
Sophocleous (1992, 1993a, 2000c), using a combination of statistical (forward stepwise regression) analysis and GIS overlay analysis, identified the portion of the GMD5 area that each recharge site or cluster of sites represents (fig. I–11), and derived an area-weighted average recharge for the GMD5 of 1.4 inches/yr based on the 1985–1990 recharge-site data, as shown in table II–28.
TABLE II–28—Recharge zonation of GMD5 based on GIS overlay analysis.
Additional details on the regionalization methodology for the Great Bend Prairie recharge are presented in Part I, Section 8.2. Additional information on GMD5 recharge can be found in Sophocleous (1992, 1993a, 1993b, 2000c).
D4. Deep Vadose Zone Study of Ground-water Recharge in the High Plains Aquifer of Southwest Kansas (Sophocleous et al., 2002; McMahon et al., 2003)
Recent improvements in technology make it possible to study the deep vadose zone, well below the rooting depths of plants. Such technology has been employed to monitor, on a continuous basis, the deep pore-water fluxes en route to the High Plains aquifer (HPA). This proof-of-concept pilot study provided, for the first time, information on the quantity and pattern of water fluxes in the deep vadose zone that impact the management of both the quantity and quality of the HPA in Kansas. The Sophocleous et al. (2002) preliminary investigation evaluated the use of heat-dissipation sensors and advanced tensiometers for measuring pore-water pressures in deep boreholes at two irrigated land-use sites (Sites 1 and 2 located in southern Finney County, fig. II–7) and one natural grassland site (Site 3 located in the Cimarron National Grassland in Morton County, fig. II–7). Continuous time-series data obtained from the heat-dissipation sensors (installed at 116 ft at the irrigated sites and at 137 ft at the grassland site) revealed constant pore-water pressures with time over the May 2000–September 2001 monitoring period.
The observed time-series patterns of pore-water pressure
head in the deep vadose zone of the High Plains imply homogenization at
depth of near-surface, temporally varying water fluxes, resulting in much
lower intensity but nearly constant (steady) recharging fluxes to the
High Plains aquifer.
The measured average hydraulic-head gradients for all sites, together with the estimated recharge fluxes based on Darcy’s law, are shown in table II–29. It is interesting to note that the hydraulic-head gradients between the deepest heat-dissipation sensor and the ground-water level at each site were approximately 0.75 for Sites 1 and 2, whereas for Site 3 it was nearly zero.
TABLE II–29—Measured hydraulic-head gradients and estimated water fluxes in deep, unsaturated High Plains sediments based on heat-dissipation sensors. Site locations are shown in fig. II–7 (adapted from Sophocleous et al., 2002).
Darcian methodology was used to obtain estimates of recharge at all the three investigation sites. Estimated recharge rates for the irrigated land-use sites (Sites 1 and 2) were appreciably higher (0.12 inch/yr and 0.02-0.04 inch/yr, respectively—table II–28) than the estimated recharge rate for the natural grassland site (Site 3; less than 0.01 inch/yr—table II–29). In all cases the estimated annual recharge values were less than one percent of annual precipitation. Although the large uncertainty associated with these estimates and the small number of study sites precludes using these flux estimates alone to draw firm conclusions regarding present-day recharge in the region, the irrigated and natural grassland sites selected are representative of irrigated and grassland areas overlying the High Plains aquifer in southwestern Kansas.
The U.S. Geological Survey conducted several chemical and tracer analyses at the aforementioned sites (McMahon et al., 2003). Chloride profile analysis (see Appendix B of Part I on tracers for recharge estimation) of the grassland site indicated that the recharge flux below the root zone ranged from less than 0.1 to 0.39 inch/yr, with an average of 0.2 inch/yr, and that estimate is considered to be a long-term (on the order of hundreds of years) estimate of recharge at the grassland site (McMahon et al., 2003). Both irrigated sites had bomb tritium (see Appendix B of Part I) and pesticides detected in both the unsaturated and saturated zones (McMahon et al., 2003), which implies a much higher recharge rate at those sites than at the grassland site.
The Darcian-based water-flux estimation aspect of this High Plains aquifer program was a pilot study of recharge assessment. That study showed that deep-vadose zone hydrology, a mostly unexplored frontier due to technological obstacles, can be monitored and analyzed. More instrumented sites, similar to the ones employed here (and taking advantage of the experience gained during this study), in combination with additional methodologies, are needed to assess the deep vadose zone water (and chemical) fluxes reaching the High Plains aquifer.
|Kansas Geological Survey, High Plains and Related Aquifers
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Web version August 2004. Original publication date April 2004.