Modeling and Field Experimentation to Determine the Effects of Terracing and Small Reservoirs on Water Supplies in the Republican River Basin above Hardy, Nebraska
* How are land terracing and small reservoir development affecting surface and ground water supplies?
The development of land terracing and small reservoirs over the last 30-40 years has had a significant but undetermined impact on basin water supplies. While these conservation projects directly impact surface water supplies, they also affect ground water recharge and potentially its impact on surface flows for years into the future. These developments affect the timing of runoff--significantly changing monthly flow distributions. A thorough water accounting that includes the effects of land terracing and small reservoirs is needed to properly manage and allocate limited water supplies and develop useful and reliable river and reservoir operating plans. This Science and Technology (S&T) Program research project will provide new tools for assessing the magnitude, distribution, and timing of impacts on surface water supplies from the development and operation of land terraces and small reservoirs.
Need and Benefit
In the Republican River Basin, there are about 1.7 million acres of terraced fields and several thousand water bodies. Estimates indicate that land terracing and small reservoir development may be depleting the natural water supply of the basin by as much as 175,000 acre-feet per year or nearly 50 percent of the historic flow measured at the Republican River near Hardy, Nebraska, where the river flows from Nebraska into Kansas. This research project will lead to a better understanding of the water balance process of water flowing into and through land terraces and small reservoirs. From this, a determination will be made of the impacts of land terraces and small reservoirs on surface water and ground water supplies. The developed methodology, including any derived values for water balance modeling parameters, should be transferable to other river basins in the Western United States.
Information gained from this study will assist with improving overall water management of the limited water supply in the basin and ensure a more appropriate allocation of water among the states of Colorado, Nebraska, and Kansas. As land terraces and small dams continue to age, better management decisions can be made on whether they should be repaired, modified, or removed. Knowledge of the depletion effect of these water conservation practices will also lead to better overall water management--including the management of existing and future conservation practices for an increased basin-wide benefit. Additionally, decisions about placement of future land terraces and small reservoirs could be made based on the expected basin-wide benefit rather than the much narrower landowner benefit. Political subdivisions could begin addressing the benefit of changing how structures are designed and placed in the watershed using the developed methodology. In the absence of the proposed study, land terraces and small reservoirs will continue to be constructed based only on considerations for the local benefit to individual landowners and not considering the benefit from a basin-wide perspective.
Information gained from this study will assist Reclamation and the States in developing reliable river and reservoir management plans that adequately address and account for all of the existing and future water uses from the available water supply. Accurate water management models are essential tools for making good operational and management decisions.
This research project is intended to enhance an ongoing cooperative study among the states of Nebraska, Colorado, and Kansas, and the United States to determine the impacts of land terracing and small reservoirs on the Republican River basin water supply. Existing funds for this study are very limited. This study fulfills a requirement of a recent settlement stipulation resolving a United States Supreme Court case concerning the enforcement of the Republican River Compact. Completion of an adequately funded study is a key component in reducing conflict and potential future litigation.
Reclamation benefits by improved management, development and protection of the very limited water resources in the Republican River basin for its projects. This research project aligns closely with Reclamation's mission of water management and priorities of honoring State water rights, interstate compacts, and contracts with water users. Reclamation also benefits from improved working relations with the states of Nebraska, Colorado, and Kansas to address water allocation issues.
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