Progress 08/01/02 to 07/31/06
Outputs
The Tamarack Ranch State Wildlife Area (TRSWA) Recharge Project is a managed groundwater recharge project that is a complex hydrogeologic and ecological system, comprised of well fields, pipelines, wetlands, artificial and natural sloughs, and streams. This project has been organized and undertaken by a recently incorporated non-profit organization of water users, the South Platte Lower River Group, Inc. (SPLRG). SPLRG is a coalition of water users and State of Colorado agencies formed to protect existing agricultural and municipal water uses while increasing river flow by 10,000 acre-feet of water during critical periods. This additional flow is Colorado's water contribution to a proposed Platte Basin Endangered Species Recovery Program, as outlined in a cooperative agreement signed between the U.S. Department of Interior, Nebraska, Wyoming, and Colorado (Cooperative Agreement). Current annual capacity of this managed groundwater recharge project is approximately 7
million cubic meters (MCM) with a future design capacity of 12 MCM. Thousands of groundwater wells in the South Platte River basin rely on similar projects as a source of river augmentation water. The goal of these projects is to enable junior groundwater appropriators to withdraw water from alluvial aquifers during high demand periods without harming senior surface water rights holders. Annual managed groundwater recharge in Colorado has increased from 24 MCM in 1980 to 220 MCM in 2005. This is a significant amount of water in a semi-arid region. This growth, along with severe drought, has brought close scrutiny to the operation and effects of such systems. A solid quantitative understanding of the interaction between these groundwater recharge systems and the river is a key to successful management of water in alluvial aquifer-stream systems. Understanding this interaction has direct impacts on irrigated agriculture, wildlife habitat, and municipal water project development. This
study used the TRSWA Project to evaluate changes in water quality and to more closely quantify how the stream-aquifer hydraulic connection affects water management in the basin. Shortcomings in commonly used analytical models were identified and improved. Field tests provided data which has already been used by several water management plans, including incorporation of this new knowledge into the official TRSWA model. Water quality was monitored and used as a tracer. The study evaluated various aspects of managed recharge projects and no significant technical flaws were found. Field testing found previous idealizations of the stream-aquifer connection to overestimate the importance of certain aspects of the connection between the aquifer and stream hydrology such as the significance of a lower permeability streambed. The overestimation is considered negligible in some applications and significant in others. The water quality monitoring was used to validate the system model and found
that water quality is affected in the riparian zone.
Impacts
There is very little field data relating stream depletion over time to wells pumping from an alluvial, tributary aquifer or alternatively, stream accretion due to recharge. Yet, thousands of wells use augmentation plans to replace water pumped from the alluvial groundwater in the South Platte and elsewhere. The information in this project is critical to water rights administration of such systems in the Western U.S. The data generated by this study has provided information on which to form a middle ground between stakeholders in conflict over basin water use. It improves information on conjunctive management. The study confirmed and improved the technical foundation for projects designed to restore wildlife habitat. The study provided data that is valuable to irrigated agriculture relying on alluvial groundwater in the basin. Finally, the project refined scientific tools used to assess groundwater-surface water interactions.
Publications
- Fox, G.A., P. DuChateau, and D.S. Durnford. 2002. Analytical model for aquifer response incorporating distributed pumping-induced stream leakage. Ground Water 40(4): 378-384.
- Miller, C.D., D.S. Durnford, and W.E. Sanford. 2006. Results of Pumping Test Assessments of the Stream-Aquifer Connection along the Lower South Platte River. 2006 South Platte Forum, Longmont, Colorado, October 25-26.
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Progress 01/01/05 to 12/31/05
Outputs
This year we completed the numerical modeling for this project, developed a methodology for estimating an equivalent hydraulic conductivity for use in analytical equations for stream depletion and continued both water quality sampling and the tracer study. We also completed the analysis of two Stream-Aquifer Pumping Tests (SAPTs) conducted by the Northern Colorado Water Conservancy District (NCWCD), Colorado Division of Wildlife (CDOW), and TZA Water Engineers. Other interested parties involved in the field test included Hydrosphere Resource Consultants, and Water & Environmental Systems Technology, Inc. The objective of the field test was to evaluate stream and aquifer parameters that govern stream depletion caused by groundwater extraction wells that operate close to the river. Our responsibility for these tests was to model the field results using both MODFLOW and analytical solutions, such as Hunt (2002), and compared model and field results. The first SAPT was
conducted using an existing recharge well near the town of Iliff, Colorado. A sand dam approximately 1000 ft upstream of the pumping well diverted river flow to the small southern channel. Groundwater discharge below the sand dam created a second channel to the north. The southern channel width varied from approximately 14 to 18 feet, while the northern channel varied from approximately 20 to 50 ft wide. Total river flow during the test was approximately 20 cubic feet per second. The pump was turned on and after the first 20 minutes of pumping, the pumping rate stabilized and held constant for the duration of the pumping period of 24 hours. Monitoring of wells continued for 16 days. Groundwater monitoring points included the pumping well, two deep piezometers, four shallow piezometers, and two irrigation wells. Stream stage was monitored at five locations and stream flow was measured periodically at four locations before, during, and after the test. The numerical model was able to
simulate drawdown exceptionally well. Stream depletion data were also well matched. Field data indicated a strong river influence. The calibration process confirmed this and appears to have provided the additional insight that no restricting streambed layer is present. The primary influence on the river depletion was found to be aquifer permeability and the rivers small footprint.
Impacts
There is very little field data relating stream depletion over time to wells pumping from an alluvial, tributary aquifer or alternatively, stream accretion due to recharge. However, this information is critical to water rights administration in the Western U.S. Our project will contribute two important data sets to this sparse database. First, we are conducting a tracer test where SF6, a conservative tracer, was injected into a recharge pond at the Tamarack Recharge Site. We have sampled from monitoring wells and analyzed for SF6 at least monthly for the last two years. Our numerical modeling of the tracer test is ongoing but it appears to compare very well with field data. Secondly, we have participated in two stream-aquifer pumping tests (SAPTs) on the South Platte. In these tests, recharge wells were pumped for a specified period of time and drawdowns in the aquifer as well as stream flow and stream stage were monitored. We analyzed the data using both numerical
and analytical models. We believe that these two SAPT data sets will be unique and very useful to water managers and researchers interested in pumping or recharging near rivers.
Publications
- Poceta, J.A. 2005. Electrical Resistivity Imaging of Eolian and Alluvial Sediments along the South Platte River, Northeastern Colorado. M. S. Thesis, Colorado State University, Fort, Collins, CO.
- Poceta, J.A., Sanford, W.E., and Harry, D.L. 2004. Mapping a Former Channel of the South Platte River within the Tamarack Ranch Wildlife Area Using Electrical Resisitivity, AGU Hydrology Days 2004, Fort Collins, CO, March 10-13, 2004.
- Miller, C.D. and Durnford, D.S. 2005. Modified use of the SDFsemi-analytical stream depletion model in bounded alluvial aquifers, Proceedings of the 25th AGU Hydrology Days, Fort Collins, Colorado, pp. 146-159.
- Miller, C.D. and Durnford, D.S. 2005. Research at the Tamarack Recharge Project and a Review of the SDF Method, Colorado WaterVolume 22, Issue 2.
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Progress 01/01/04 to 12/31/04
Outputs
An important component of this project is to quantify the flow paths and seepage velocities of water injected into recharge ponds as it travels through the alluvium to the receiving South Platte River. We have taken a multi-faceted approach to this by completing a numerical model based on extensive field data and then verifying the results of the model using a long-term field tracer study. The combination of modeling and extensive field verification for managed recharge systems is unique to this project and will lend credibility to our results, as well as serve as a model for similar projects. We completed the calibrated numerical flow model of the aquifer system last year but confidence in model results depends on verification using detailed field information. This year, to verify the model, we began the long-term tracer test. The tracer was injected into the primary recharge pond for 5 days while the recharge ponds were operational, followed by a week of flushing.
Samples from an extensive well network were collected biweekly or monthly and analyzed for the tracer. Early results showed an unexpected high dispersivity but the center of mass of the tracer is consistent with that predicted by the model. Sampling for the tracer is continuing. In addition to verification of the model, tracer techniques were developed that should be useful to other similar projects. The calibrated and verified model will be used to predict flow augmentation from the recharge system, as well as water quality and quantity effects on on-site hydrologic features such as the backwater sloughs and wetlands. Using both extensive field data collection and modeling in this project, we have developed a defendable model and new methods to predict the effects of pumping and recharge on flow augmentation at other sites along the Platte River. Methods developed in this project are already being used in evaluating water rights applications as the junior well owners along the South
Platte file with the water courts in Colorado.
Impacts
Managed groundwater recharge systems have increased from less than 20,000 acre-feet annually to over 100,000 acre-feet annually in the last two decades and they are expected to continue to increase. This project offers an anticipatory perspective on the impacts of this augmentation on water quality and quantity in the receiving surface water and alluviums. In addition, we are developing methods that more accurately characterize and model the hydrologic linkages between surface and ground water. These methods will be useful in similar river basins and ecosystems in the Western U.S.
Publications
- Sanford, W.E., 2004, A long-term tracer test at a recharge pond using sulfur hexafluoride and applied deuterium: Geological Society of America Abstracts with Programs, v. 36, no. 5, p. 395.
- Poceta, J.A., W.E. Sanford and D.L. Harry, 2004,Electrical resistivity imaging of the Tamarack Ranch State Wildlife Area, Northeastern Colorado, Proceedings, Geological Society of America, Nov. 7-11, 2004.
- Miller, C. and D. Durnford, 2004, A review of the SDF semi-analytical stream depletion modeling bounded alluvial aquifers. Abstract. 15th Annual South Platte River Forum, Longmont, CO.
- Miller, C. and D. Durnford, 2004, Large scale subsurface dams in alluvial aquifers: Potential for new water storage for Colorado? Abstract. 15th Annual South Platte River Forum, Longmont, CO.
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Progress 01/01/03 to 12/31/03
Outputs
The first phase of the water quality study has been completed. Results clearly show water quality constituents transferring from the river to the alluvium. Based on these results, we can extrapolate to the long-term water quality effects of augmentation on the South Platte alluvium. In addition, the numerical groundwater model is complete and calibrated and being used to consider alternative physical and hydrologic controls on the groundwater recharge system to better meet project objectives for river augmentation and habitat. Seismic surveys were completed in summer, 2003 and interpretation of the data is ongoing. A preliminary tracer test (bromide) was completed in the first year of this project. A more complex tracer test using SF6 is planned for mid-March, 2004. We have completed the preliminary planning and analysis methods development for this test.
Impacts
Managed groundwater recharge systems have increased from less than 20,000 acre-feet annually to over 100,000 acre-feet annually in the last two decades and they are expected to continue to increase. This project offers an anticipatory perspective on the impacts of this augmentation on water quality and quantity in the receiving surface water and alluviums. In addition, we are developing methods that more accurately characterize and model the hydrologic linkages between surface and ground water. These methods will be useful in similar river basins and ecosystems in the Western U.S.
Publications
- Watt, J. 2003. Water quality changes at a streamflow augmentation project, Lower South Platte River, CO. M.S. Thesis, Colorado State University, Fort Collins, CO.
- Watt, J. 2003. Preliminary investigation into the effects of managed recharge on water quality. Proc. 23rd Annual Geophysical Union Hydrology Days, J.A. Ramirez (ed.), Fort Collins, CO.
- Fox, G.A. 2003. Improving MODFLOW's RIVER package for unsaturated stream/aquifer flow. Proc. 23rd Annual Geophysical Union Hydrology Days, J.A. Ramirez (ed.), Fort Collins, CO. p. 56-67.
- Fox, G.A. 2003. Estimating streambed and aquifer parameters from a stream/aquifer analysis test. Proc. 23rd Annual Geophysical Union Hydrology Days, J.A. Ramirez (ed.), Fort Collins, CO. p. 68-79.
- Fox, G.A. 2003. Modeling of stream/aquifer interaction during alluvial well depletion. Ph.D. Dissertation. Colorado State University, Fort Collins, CO.
- Fox, G.A. and D.S. Durnford. 2003. Stream/aquifer analysis tests: Estimating streambed and aquifer permeability. Colorado Water 20(3): 5-7.
- Fox, G.A. and D.S. Durnford. 2003. Unsaturated hyporheic zone flow in stream/aquifer conjunctive systems. Advances in Water Resources, 26(9): 989-1000.
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Progress 01/01/02 to 12/31/02
Outputs
This is the first year of a project that will characterize the hydrology and water quality effects of a managed recharge project on the South Platte River in Eastern Colorado. Managed recharge redistributes water in time. During high-flow, low-demand periods, water is pumped from the alluvium near the river (effectively withdrawing water directly from the river) and piped to recharge ponds where it is allowed to infiltrate. This water returns to the river through subsurface flow, augmenting the river flow during low-flow, high-demand periods. The timing and quality of these return flows and their effect on water quality and quantity in the alluvium, river and backwater sloughs are the subject of this research. We have completed a numerical groundwater model of the study site, in conjunction with the Colorado Department of Wildlife and Northern Colorado Water Conservancy District. We have also completed the first phase of a tracer study and continue to sample water
quality in the groundwater, recharge ponds, backwater sloughs and river on a biweekly or monthly basis. Preliminary results indicate that the augmentation system is significantly affecting the hydrology of the study site and riparian area as well as water quality of these areas. In particular, data show that backwater sloughs that are the primary habitat for minnows-of-concern have water quality similar to the river in some cases and to the groundwater in other cases. Differences in temperature and water quality are significantly different depending on the source of water and these differences are expected to result in variable habitat in these sloughs.
Impacts
Managed recharge is an increasingly common form of flow augmentation in the Western U.S. This project will provide an increased understanding of the water quality and quantity impacts of managed recharge projects. In addition, the hydrologic connection between the groundwater and surface water is of interest in most conjunctive use projects.
Publications
- Watt, J., W. Sanford, D. Durnford and J. Stednick. 2002. Hydrogeologic Investigation into the effects of managed recharge on water quality, Lower South Platte River, CO. Paper 102-5, Section T61, Annual Meeting of the Geological Society of America, Denver, CO. October 22-24, 2002.
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