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<br />. <br /> <br />. <br /> <br />. <br /> <br />, . <br /> <br />Problem: High Groundwater Flooding <br />DRAFT Water Committee Subgroup Report <br />February 2, 1999 <br /> <br />At the January 5th Water Committee a subgroup was formed to prepare a proposed approach <br />to analyze the groundwater flooding problem in Central Platte River valley. A meeting was <br />held January 28th at Central Platte NRD to work on developing a approach. See attached list <br />of those attending. At the meeting the group discussed four basic areas of analysis; surface <br />water stage, groundwater levels, groundwater recharge and data collection to surveys the <br />extent of flooding. <br /> <br />Surface water stage analysis <br /> <br />The purpose of this analysis is to compare historical river stages to those that could occur with <br />the CA program. The historic river stages recorded by USGS and DWR at the major flow <br />stations in the Central Platte River need to be compiled to develop stage hydro graphs for a <br />selected period of record. The period of record would need to be set based on past climatic <br />conditions representing high and low flow conditions. The future river stage values would <br />then need to be developed based on operational changes estimated for the CA program. The <br />comparison between past and future river stages can then be made to see the extent and <br />magnitude of river stage changes. These changes can then be used in the analysis of <br />groundwater movement into and out of the river. <br /> <br />Analysis of Groundwater Levels <br /> <br />The purpose oflooking at groundwater levels is to show the extent of historical changes, to <br />develop depth to groundwater maps showing problems areas, to develop a data set to look for <br />relationships with river stage and net recharge, or calibrate a groundwater model with. There <br />are several levels of data collection efforts for groundwater levels in the Central Platte River <br />area 1). Wells which record continusaly, 2). Wells with water levels read monthly, and 3). <br />Wells read semi annually Spring and Fall. The groundwater flooding happens mainly in the <br />Spring of the year so the depth to water maps that would be most helpful in looking at the <br />historical changes would be the Spring readings collected in late April or early May. <br />Continuous or monthly data would be needed to try an correlated river stage to groundwater <br />level. A simple correlation of river stage to groundwater level does not answer question about <br />cause and effect (is groundwater levels effecting river stage or is river stage effecting <br />groundwater). The group discussed using a bank storage function as one means to estimate <br />the effect of river stage on groundwater. We also discussed the use of groundwater models to <br />estimate the relationship of groundwater and surface water. <br /> <br />Groundwater Recharge <br /> <br />The purpose of analyzing groundwater recharge is to estimate the potential effect of <br />precipitation events over time on groundwater storage. Using existing soil moisture budget <br />programs or other techniques using precipitation as a input compute a estimate of net recharge <br />