Progress 07/01/04 to 06/30/08

Outputs
OUTPUTS: The results from this project have been disseminated through presentations to interested water resource management state and local agencies, including The Nature Conservancy, the State Engineer's Office, the Colorado Division of Wildlife, the Colorado Water Resources Research Institute, and the Republican River Water Conservation District. Results were also disseminated through referred journal publications, several M.S. theses and publication in Colorado Water, a newsletter of the Water Center at Colorado State University. PARTICIPANTS: Collaborators on this project include: Dr. Kurt Fausch and Jeff Falke, Department of Fish, Wildlife and conservation Biology; Dr. Ramchand Oad, Linda Riley and Steven Griffin, Department of Civil and Environmental Engineering; and William Burnidge, The Nature Conservancy. Support for Dr. Fausch and his students was provided by the Colorado Division of Wildlife. Three graduate students were trained in groundwater modeling for water management as a result of this project. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Across the western Great Plains, groundwater pumping for irrigated agriculture is depleting regional aquifers that sustain stream flow for native fishes. In conjunction with researchers in the Fish and Wildlife Conservation Department at CSU, we surveyed fish habitat quantity and connectivity in the Arikaree River in eastern Colorado at multiple spatial scales during spring and summer 2005-2007 to investigate habitat loss for imperiled native fishes. At the basin scale, flowing reaches were reduced from 65 to <15 km by late summer, and long permanently dry segments in the lower basin now prevent recolonization. Based on this fish habitat data, and historical groundwater and stream flow data, we constructed a MODFLOW groundwater model to predict how pumping will affect groundwater stage and fish habitat under three future scenarios. With status quo pumping, refuge pools in the wettest segment are reduced by half in 25 years (2035). Results were identical after removing two alluvial wells upstream. Likewise, the current state policy of retiring wells within a 4.8-km band around the river to meet an interstate water compact resulted in only 55% of pools remaining in 35 years, nearly all isolated in a 1.7-km fragment upstream. A water balance model indicated that maintaining current alluvial groundwater levels and refuge pools for fishes would require at least a 75% reduction in groundwater pumping, which is not economically or politically feasible. Given widespread streamflow declines due to groundwater pumping, the future for stream fishes in high plains streams is bleak, and managers will be challenged to conserve native fishes under current pumping regimes. The results of this project not only serves as a warning to water managers that groundwater-fed streams will not survive under current groundwater pumping scenarios, but it also suggests ways in which this future can be changed.

Publications

• Falke, J.A., Fausch, K.D., Magelky, R., Squires, A. Durnford, D.S., Riley, L.K. and Oad, R. The role of groundwater pumping and drought in shaping ecological futures for stream fishes in a western Great Plains river basin. Submitted to Ecological Applications, December, 2008.
• Aldred, A., Riley, L., Durnford, D., Oad, R., Falke, J. and Fausch, K. Evapotranspiration along a High Plains Stream: Comparison of the Water-Table Fluctuation and Numerical Response Function Methods. In Preparation, to be submitted January, 2009.
• Squires, A. 2007. Groundwater response functions and water balances for parameter estimation and stream habitat modeling, M.S. thesis, Civil and Environmental Engr., Colorado State University, Fort Collins, CO.
• Riley, L. Finding the Balance: A case study of irrigation, riparian evapotranspiration and hydrology of the Arikaree River Basin, M.S. Thesis. Colorado State University. Fort Collins, CO. Expected Spring, 2009.
• Banning, R. Analysis of the Groundwater/Surface Water Interactions in the Arikaree River Basin of Eastern Colorado. M.S. Thesis, Colorado State University. Fort Collins, CO. Expected Spring, 2009.
• Magelky, R. Future Predictions of River Ecosystem Health using Numerical Modeling of Groundwater\Surface Water Systems. M.S. Thesis, Colorado State University, Fort Collins, CO. Expected Spring, 2009.

Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: In June, we presented results of our research to the State Engineer's Office. In November, 2007, we organized a more extensive half day meeting at Colorado State University to present our research results to several agencies. Invitees included the Colorado Division of Wildlife, the State Engineer's Office, the Colorado Agricultural Experiment Station, the Colorado Water Resources Research Institute, the Republican River Water Conservation District and The Nature Conservancy. The purpose of the meeting was to present our research results and obtain feedback for planning our next steps. The meeting was well attended and response was positive. In addition, we have shared our results with interested water groups and individuals through the newsletter of the Water Center of Colorado State University "Colorado Water" and numerous discussions with individuals and agency personnel. PARTICIPANTS: Individuals: Principal Investigator: Deanna Durnford, Professor, Civil and Environmental Engineering, Colorado State University, Fort Collins, CO. M.S. Students: Angela Squires, Robin Magelky, Civil and Environmental Engineering, Colorado State University, Fort Collins, CO Collaborators: Kurt Fausch, Professor, Department of Fish, Wildlife and Conservation Biology, Colorado State University. Jeff Falke, Ph.D. student, Department of Fish, Wildlife and Conservation Biology, Colorado State University. Ramchand Oad, Professor, Civil and Environmental Engineering, Colorado State University, Fort Collins, CO. M.S. Student: Linda Riley, Civil and Environmental Engineering, Colorado State University, Fort Collins, CO. Partner Organizations: Colorado Division of Wildlife and The Nature Conservancy District.

Impacts
As a direct result of our November 2007 research meeting with state and local water agencies, The Nature Conservancy (TNC), working with the Republican River Water Conservation District, has undertaken a program to retire three active wells and two additional inactive wells near the Arikaree River identified in our research project as those that would most benefit the flow in the "live" stretch of the river. TNC is seeking approximately $100,000 to retire these wells, which would be matched by approximately $491,000 from other programs to achieve the projected benefits. In addition, the Colorado Division of Wildlife agreed to provide more funding for our colleagues in Fish and Wildlife Biology to continue their study of fish habitat. The target wells are located upstream of the Fox Ranch, which is owned and operated by TNC for a range of conservation objectives including habitat for the native plains fish. The Fox Ranch was acquired with financial assistance from the Colorado Division of Wildlife (Wetlands Program) and the US Fish and Wildlife Service to protect the significant riparian and aquatic resources of the Arikaree on the ranch. Retiring wells along the Arikaree will yield compact compliance benefits, increase the quality of the aquatic and riparian habitat near the river and reduce erosion and the loading of sediment and nutrients into the Arikaree river. In addition to the on-ground results in the Arikaree River Basin, our research has led to two new contributions to the state of knowledge. First, our models have been shown to be able to predict river water level changes on daily and weekly time steps due to stresses such as pumping and evapotranspiration in both the alluvial and regional aquifers. To our knowledge, this has not been reported in the scientific literature. Thus, we have developed an excellent tool to predict effects on aquatic habitat due to changes in the future. Secondly, our research included an extensive evaluation of the evapotranspiration rates of phreatophytes. Data from this component of the project contributes to the very slim, but critical, knowledge base related to phreatophyte evapotranspiration.

Publications

• Squires, Angela. 2007. Groundwater Response Functions and Water Balances for Parameter Estimation and Stream Habitat Modeling. M.S. Thesis, Civil and Environmental Engineering, Colorado State University, Fort Collins, CO.
• Durnford, D., Squires, A., Falke, J., Fausch, K., Oad, R. and Riley, L. 2007. Aquicultural and Water Management Alternatives to Sustain a Vulnerable Aquatic Ecosystem on the Eastern High Plains of Colorado. Colorado Water: Newletter of the Water Center of Colorado State University. Vol. 24 (5): 14-19.

Progress 01/01/06 to 12/31/06

Outputs
The goal of this project is to model the critical hydrologic linkages between center-pivot pumping for irrigation from an alluvial aquifer and stream habitat required for survival and reproduction of a threatened fish species. Decline of the Ogallala Aquifer due to groundwater pumping for center-pivot irrigation of crops is one of the most important environmental and economic problems associated with agriculture on the Great Plains. The aquifer sustains both an important agricultural economy and most of the aquatic and riparian ecosystems in the region, and both are in trouble. This project will predict the effects of a five-year drought on stream hydrology and fish persistence under various future scenarios. To date, we have completed the development and calibration of a large-scale (regional) numerical groundwater/surface water model. However, it has become clear that the temporal and spatial scale relevant to the fish habitat is much smaller than the regional-scale model. Therefore, we are writing code for a smaller scale model that will incorporate just the alluvium and time scales that are daily or weekly. We will imbed this new model in the regional model.

Impacts
We believe that our study site, the Arikaree River, is at a "critical threshold", as are other groundwater-sustained streams in the high plains. A high concentration of center-pivot irrigation systems, a declining water table, a strong link between groundwater pumping and stream baseflow, the presence of a state-threatened fish, a precarious local agricultural economy, an exploding population willing to pay high prices for water rights and finally, state and local agencies and local farmers primed by a recent severe multiyear drought make this a timely and important study. The long-term consequences of failing to research and protect the future of this river include the real possibility that there may soon be no river. The research proposed is especially timely because the State of Colorado is expected to spend over $62 million dollars over the next 15 years to take 30,000 center-pivot irrigated acres out of production in the basin of our study site to meet a recent interstate water compact. This "irrigation forbearance" program will enroll producers based only on the distance between the well and the river. Our research has already helped The Nature Conservancy identify center-pivot systems that will not only meet compact requirements, but also are most important in protecting core aquatic habitat.

Publications

• No publications reported this period

Progress 01/01/05 to 12/31/05

Outputs
The study site for this project is the Arikaree River on the high plains of eastern Colorado. This is a small stream that is almost entirely sustained by the regional High Plains Aquifer and one that is habitat for a state-threatened fish, the brassy minnow. As part of an interdisciplinary project, we are investigating the effect of center-pivot pumping for crop irrigation on the stream hydrology and the stream ecosystem. We have completed an initial numerical groundwater model for the upper reaches of the study area near The Nature Conservancy Fox Ranch. The model was calibrated for steady state conditions using predevelopment water table data. We also completed a field study to predict the evapotranspiration rates of the phreatophytes near the river. From our preliminary field study and computer modeling, it appears that evapotranspiration of the riparian vegetation (primarily phreatophytes such as willows and cottonwoods) from the shallow alluvial aquifer near the stream is playing a much bigger role in the stream drying inter-season cycle than the large-scale center pivots pumping from the regional aquifer. On the basis of this preliminary modeling, we hypothesize that the high capacity center pivot irrigation systems are mining the regional High Plains Aquifer, resulting in the measured water table decline of about a foot per year. However, they do not draw down water levels in the stream significantly within a single growing season. This has important implications with regard to strategies based on irrigation forbearance to protect aquatic ecosystems from short-term drying during a summer season. We will model the center pivot irrigation effects with a large-scale regional model of the High Plains Aquifer using a coarse grid spacing. Assuming, however, that the stream stage variation within a season more closely reflects the evapotranspiration pattern for the riparian vegetation, we will model the alluvial aquifer, flood plain, riparian vegetation and river will be modeled on a smaller grid. The connection between the regional and local scale models will be through a general head boundary condition for the alluvial aquifer, which will reflect the long-term trend in regional water table declines.

Impacts
Both the phreatophyte vegetation withdrawing water from the alluvial aquifer and the high capacity center-pivot irrigation systems pumping from the regional High Plains Aquifer affect the stream hydrology and, hence, the aquatic ecosystem. However, it appears that the timing of the two effects on the stream is significantly different. In earlier work, there was a strong correlation noted between the pumping pattern for irrigation and the drawdowns and recovery measured in the stream. However, from our modeling, it appears that this correlation is not direct and, in fact, the primary effect of pumping is the long-term decline of the regional water table, which over years and decades will lower the influx to the alluvial aquifer. It does not, however, relate to the seasonal stream stage fluctuations directly. This has significant implications for irrigation forbearance, which is being proposed at many locations in the arid West as a response to drought when aquatic ecosystems are vulnerable. These early results would suggest that turning off an irrigation well may not result in a timely response of the stream. We will continue to investigate the relative importance of near-stream vegetation and high capacity pumping on the dynamics of the stream.

Publications

• No publications reported this period

Progress 01/01/04 to 12/31/04

Outputs
The project site is the Arikaree River basin in Eastern Colorado. Flow in the Arikaree River is entirely sustained by the Ogallala Aquifer and it is also the last stronghold in Colorado of the brassy minnow, a state-listed threatened fish species. Since water levels in the aquifer are declining, it is expected that continued high capacity pumping from the aquifer will dry critical reaches of the Arikaree River, negatively impacting fish survival. To address this issue, two questions must be answered initially. First, what is the extraction by the riparian phreatophyte vegetation and the impact of this extraction on the streamflow in the Arikaree River? Second, how much water is used by the center pivots near the river for irrigation and what is the impact of the center pivot irrigation systems on the baseflow of the river? To address these initial questions and provide input needed for later modeling efforts, a network of monitoring wells was installed this year. In addition to monitoring water levels in the aquifer, water levels in the stream and streamflows are being measured at preselected time intervals. This information will allow us to estimate inputs to a numerical groundwater model that will be developed in the second phase of this project and also provide water level data for model calibration. The ultimate goal of the project is to determine hydrologic linkages between the center pivots and the stream so that center pivots can be retired or irrigation temporarily curtailed to maintain minimum critical fish habitat during drought years.

Impacts
Agricultural economies and aquatic ecosystems on the High Plains of Colorado are largely sustained by the Ogallala Aquifer. Farmers in these areas subsist on very low profit margins and their crops are largely dependent on groundwater for irrigation. Rivers in these areas are also dependent on groundwater baseflow. In the last few decades, large scale center pivot irrigation has led to regional declines in the water table, resulting in reduced baseflow to the rivers and increasingly dry stream reaches. This results in negative impacts on aquatic/riparian ecosystems. In particular, some threatened fishes are declining. An example is the brassy minnow. This species was once widely distributed in northeastern Colorado. Now, its distribution is restricted almost entirely to about 50 km of the Arikaree River near the Kansas border. To sustain both a precarious regional agricultural economy dependent on groundwater for irrigation, and an aquatic/riparian ecosystem likewise dependent on groundwater for existence, it is clear that we must develop the knowledge required to predict tradeoffs in use of this scarce resource. This project will determine the hydraulic linkages between selected center-pivots and these critical river reaches, and develop a protocol for selecting wells that will have the most impact on fish survival. This information will be useful to water managers and irrigators. Possible solutions include permanent removal of center pivot systems that are most critical or irrigation forbearance during drought years to protect critical stream reaches.

Publications

• No publications reported this period