The State of Kansas has entered into a WaterSMART basin study with the States of Colorado and Nebraska and the U.S. Bureau of Reclamation. The purpose of the Republican River basin study is to assess current and future imbalances between water supplies and water demands in the basin and evaluate alternatives that may more effectively manage the water. Future water supply and demand will depend on future climate conditions, including long term averages and variations in precipitation and temperatures over the basin.
Climate plays an important role in water supply and demand. Precipitation determines how much irrigation is needed, drives surface runoff and provides recharge to groundwater. Air temperature is strongly correlated to potential evapotranspiration. High temperatures are associated with increased evapotranspiration and increased vegetation water demand. Climate influences the interactions and feedbacks in hydrologic processes. For example, the amount of runoff or recharge from a specific storm event depends in large part on the soil moisture conditions within the watershed. The timing and intensity of a storm event also plays a large role.
Computer hydrologic models are a key tool used in the future conditions assessment. The groundwater model developed for the Republican River Compact Administration (RRCA) will be used in Colorado, the Upper Republican basin in Kansas, and the full stretch of the basin in Nebraska. The RRCA model never extended down into the lower Republican basin in Kansas. Kansas is developing a groundwater-surface water model, called HydroGeoSphere, from Harlan County Lake, Nebraska, down to the stream gage near Clay Center, Kansas. Kansas is also developing a system operations model, called Oasis, to project the water stored and released from Harlan County and Lovewell reservoirs and the irrigation canals.
The study will evaluate current (2010) and projected future (2060) conditions. Future projections will include potential climate change scenarios of warmer and wetter, and less warmer and drier, as well as a central tendency climate condition. Projected precipitation, temperature and evapotranspiration data, downscaled from global climate models, will be provided by Reclamation for the States to input into the water models.
Five structural alternatives will be evaluated in the basin study. In addition to evaluating the water management impact, each alternative will also be evaluated for its economic and environmental impacts, and an estimated cost to implement. The WaterSMART basin study will be completed December, 2014.