GROUND WATER/SURFACE WATER INTERACTIONS 1-3 AWRASUMMER SPECIALTY CO C& 2002

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JULY GROUND WATER/SURFACE WATER INTERACTIONS 1-3 AWRASUMMER SPECIALTY CO C& 2002 COMPARISON OF METHODS TO ESTIMATE STREAMBED SEEPAGE RATES Marisa Cox, Don Rosenberry*, Grace Su, Terrence Conlon4,

1 JULY GROUND WATER/SURFACE WATER INTERACTIONS 1-3 AWRASUMMER SPECIALTY CO C& 2002 COMPARISON OF METHODS TO ESTIMATE STREAMBED SEEPAGE RATES Marisa Cox, Don Rosenberry*, Grace Su, Terrence Conlon4, Karl Lee4. and Jim Constantz ABSTRACT: Quantifying streambed hydraulic properties is necessary for understanding stream exchanges with shallow groundwater. Measurement of seepage rates aids in quantifying these hydraulic properties. Temperature-based, seepage-meter based, and seepage run flux estimates were compared in the Russian River, CA and four streams in the Willamette Valley, OR. Temperature-based methods rely on inverse modeling to match simulated sediment temperatures to observed temperatures, while the seepage-meter methods measure the flow of water across a confined area of the streambed. Seepage run estimates measure the volumetric change in streamflow at the head and base 2f a stream Tach. Seepage flux from the stream to the groundwater in the Russian River ranged from 1.1~10~~ to 6.9~10, mls. In the Willamette Valley, seepage flux from groundwater to the stream ranged from 5x10- to 8.8~10- mls. In general seepage flux estimates obtained with a temperature-based method were higher than those obtained with the seepage-meter, though comparisons were quite close for the Russian River sites. KEY TERMS: temperature; seepage meter; seepage; seepage runs. INTRODUCTION Quantifying exchange between stream water and shallow groundwater is important to current hydrologic issues ranging from water quality to water supply and stream management. Several methods have been used to quantify stream groundwater exchange including tracer dilution techniques, seepage runs, seepage-meters, temperature profiling, and hydraulic-head gradients. No one approach can describe the spatial variability of streambed exchange that occurs over scales pertinent to hydrologic issues. Combining two or more approaches improve the reliability of hydrologic measurements and broaden their applicability to reach scale issues. Three techniques for measuring hydrologic exchange in steams are compared in this study. 1) Temperature-based methods determine groundwater discharge and recharge, and provide information on spatial variability of hydrologic exchange within a reach. Temperature-based methods can incorporate temporal variability in flux rates because they collect data at discrete time intervals. 2) Seepage-meters determine the variability of groundwater discharge and recharge at specific locations in a streambed. They provide insight into local-scale streambed heterogeneity. Repeated measurements of seepage rates along a stream reach accentuate the complexity of the stream water groundwater exchange. 3) Seepage runs determine the magnitude of flow increase or decrease along a reach, including inputs from tributaries and groundwater and outputs due to groundwater recharge, streambank storage, and evapotranspiration. Seepage runs are limited by the ability to measure discharge, and by the increase or decrease in streamflow along a stream reach relative to the initial streamflow. Seepage runs provide a spatially averaged picture of stream water exchange with shallow groundwater. By estimating the major groundwater sources and sinks along a reach, hydrologic, chemical and biologic processes related to water quality and source issues can be elucidated. Study Area Two study areas were selected to compare techniques for estimating streambed seepage rates. The first study area consisted of three sites on the Russian River in Northern CA. Two of the sites were located directly in I USGS, 345 Middlefield Rd, Menlo Park, CA 94025, Phone: (650) , Fax: (650) , mhcox@usgs.gov. USGS MS 413, Bldg. 53, DFC, Lakewood, CO USGS, 345 Middlefield Rd, Menlo Park, CA 94025, USGS SE Cherry Blossom Dr., Portland OR,

the river and the third site was located in a recharge pond adjacent to the river. Temperature-based flux estimates were compared with seepage-meter estimates in the Russian River.

2 the river and the third site was located in a recharge pond adjacent to the river. Temperature-based flux estimates were compared with seepage-meter estimates in the Russian River. The second study area had five sites in four streams in the Willamette Valley, OR. Seepage flux was compared using temperature-based methods, seepage-meters, and seepage runs. Methods The temperature-based method measures temperature patterns in the stream and underlying streambed, which are governed by the rates of heat exchange between the atmosphere and stream. Heat exchange between the stream and the underlying streambed sediments dampens the diurnal heat signal seen in the streambed sediments (Figure 1); however, a diurnal variation with a phase lag is still detected at considerable depth. It is the phase lag that is used to estimate water flux. Measurement of sediment temperature over time at two or more depths is required to estimate the rate of heat transfer through the streambed. For purposes of inverse modeling in this study, the upper boundary condition is the observed stream temperature and the regional groundwater temperature approximates the lower boundary condition. The temperature-based method requires temperature to be continuously monitored at fixed locations within a piezometer (Figurel). A single-channel, submersible microdata logger continuously monitored temperature in the piezometer and surface water. Seepage flux was estimated by matching measured water temperatures beneath the streambed (Thomas et al, 2000) with surface water temperatures simulated with a I-dimensional heat transport model (VS2DH, Healy and Ronan, 1996). A seepage-meter is an open ended drum pushed into the streambed that measures the amount of water that flows across the sediment-water interface; a plastic bag is used to record the change in volume over time (Figure 1). In this study, a 57 cm diameter drum was used with a side valve connected to a plastic bag. The seepage-meter bag contained a known volume of water upon connection to the drum, and was removed after a timed period to obtain the volume change. Equilibration times ranging from 1 to 12 hours were allowed between drum installation and attachment of the bag for measurements. Numerous researchers have used seepagemeters in a range of streambed and lake settings (e.g.', Lee, 1977; Lee and Cherry, 1978; Rosenberry, 1990; Duff et al., 2000; and Rosenberry, 2000). Seepage runs estimate seepage flux by calculating the difference in stream flow at the head and base of a stream reach after accounting for tributaty inflows, diversions, and travel-time of water within the reach (Riggs, 1972). Seepage runs were performed only in the Willamette Valley, OR field site. water ~... <\, :,.,.. / \ I Figure 1. Temperature and Seepage-meter Instrumentation 520

3 Results Russian River, CA Seepage flux estimates by temperature-based and seepage-meter methods were comparable at all sites (Figure 2). At all sites, river water was being lost to the shallow groundwater system. At Steelhead, the temperature-base! estimates taken over ten days (8.3~10~ mls) were comparable to short term seepage-meter estimates (3.8~10- mls) (Figure 2). At WhoJer, only a seepage-meter was used to estimate seepage flux. The average seepage flux for Wholer was 9.3~10 mls (Figure 2). In the recharge pond, the temperature data loggers malfunctioned during the time that seepage-meters estimates were being made so the seepage flux rates for the temperature-based method are linear extrapolations from continuous data for the previous two months The highest seepage rates were at the North and Ea$ sites. The temperature-based method estimated seepage flux to be 1.0x106m/s for the North site and 1.7~10 mls fo: the East site (Figure 2). By CoTparison the seepagemeters estimated the average seepage flux to be 4.3~10 mls for the North site and 1.3~10- mls for the East site. The S$uth site had the lowest seepage rate. The temperature-base$ method estimated seepage flux to be 1.Oxlo- mls and the seepage-meter estimated the seepage to be 6x10- mls (Figure 2). For all but the North site at the recharge pond, the seepage rates calculated with the temperature-based method were higher than the rates calculated from the seepage-meter m F 0 = 100 Q) ul 1 0 Seepage meter H Temperature 0 f Steelhead Wholer North South East Recharge Pond Figure 2. Comparison of Seepage Estimates at the Russian River Sites Willamette Valley, OR The Seepage flux results were compared for the temperature-based method, seepage-meter method and seepage run for the sites in the Willamette Valley (Figure 3). All of the reaches were in areas expectfd to gain water due to shallow groundwater discharge. At Butte Creek, seepage flux was estimated to be 1x10. mls with the seepage-meter method and 8x10.' mls with the seepage run (Figure 3). This seepage run estimate was within the uncertainty of the discharge measurements made. At Case Creek, seepage flux was estimated to be 6~10.~ mls with the temperature-based method and 1~10.~ mls with the seepage-meter (Figure 3). At the Upper Pudding River, seepage was estimated to be 2xlO~'mls with the seepage-meters. The seepage run estimated a loss of water at the Upper Pudding River site with a seepage rate of 8x10.' mls; however, this estimate was within the uncertainty of the discharge measurement. At the Lower Pudding River, seepage was estimated to be 521

4 3~10-~mls with the temperature-based method, 5x10. mls with the seepag%-meter and ~xio-~, mls with the seepage run (Figure7 3). At Zollner Creek, seepage was estimated to be 4x10 mls with the temperature-based method and 8.8~10- mh with the seepage-meters. The temperature-based method resulted in a higher seepage flux estimate compared to the seepage-meter method at two of the three sites in the Willamette Valley. The seepage run flux estimates were higher than the seepage-meter estimates at Butte Creek and Lower Pudding River Seepage (IO%l/S) r I OSeepage run Temperature 0 Seepage meter i Butte Case Upper Lower ZOilnel Creek Creek Pudding River Pudding River Creek Figure 3 Comparison of Seepage Estimates for the sites in the Willamette Valley, OR Summary In general, the temperature-based estimates of seepage rates were larger than seepage-meter estimates. However, studies show that seepage-meters tend to under estimate seepage rates due to the unavoidable constriction between the large volume of the meter and the accompanying measuring device (Eelanger and Montgomery, 1992). If characterization of temporal and spatial variability is important, temperature-based methods may be preferred in most stream environments, though at low seepage the method uncertainties of temperature-based seepage rates increases unless thermal parameters are accurately determined. ACKNOWLEDGEMENTS The Sonorna County Water Agency (SCWA) provided funding for the Russian River work. We would like to thank Jay Jasperse and Don Seymour at SCWA for their support. Funding for the seepage measurements in the Willamette Valley, OR was funded, in part, by the Oregon Water Resources Department (OWRD). Karl Wozniak, a hydrologist at OWRD was instrumental in finding suitable sites and installing the piezometers. REFERENCES Eelanger, T.V., and M.T. Montgomery, Seepage meter errors. Limnol. Oceanogr., 37:

5 Duff, J.H, Toner, B., Jackman, A.P., Avanzino, R.A., Triska, F.J Determination of groundwater discharge into a sand and gravel bottom river: a comparison of chloride dilution and seepage meter techniques. Verh. Internat. Verein. Limnol. 27: Healy, R.W., and Ronan, A.D., Documentation of computer program VS2DH for simulation of energy transport in variably saturated porous media: USGS Water-Resources Investigations Report , 36p. Lee, D.R., A device for measuring seepage flux in lakes and estuaries. Limnol. Oceanogr. 22: Riggs. H.C, Low-Flow Investigations: USGS Techniques of Water-Resources Investigations Book 4 Chapter BI, p Rosenberry, D.O., Inexpensive groundwater monitoring methods for determining hydrologic budgets of lakes and wetlands, in proceedings of the 1989 National Conference on Enhancing the States Lake and Wetland Management Programs, N Am Lake Manage. SOC., Chicago, Ill. Rosenberry, D.0, Unsaturated-zone wedge beneath a large, natural lake. Water Resour. Res., Thomas, C, Stewart, A.E., and Constanh, J., Comparison of methods to determine infiltration rates along a reach of the Santa Fe River near La Bajada, New Mexico. USGS Water Resources Investigations Report ,65p. 523

GROUND WATER/SURFACE WATER INTERACTIONS AWRA SUMMER SPECIALTY CONFERENCE Judith Schenk'

July 1-3 GROUND WATER/SURFACE WATER INTERACTIONS AWRA SUMMER SPECIALTY CONFERENCE 2002 326x6 pjf= INTEGRATION OF DATA USING GIS AND STATEPP TO ESTIMATE GROUNDWATER MODEL INPUT PARAMETERS Judith Schenk'