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<br />C00004 <br /> <br />USDA-NRCS Area Office in La Junta, Southeastern Colorado Water Conservancy Distric~ the Pueblo <br />Subdistrict Office of the USGS, the Eastern Colorado Area Office of the USBR, the District-II Office of the <br />Colorado Division ofWatet Resources, the USDA Farm Services Agency, and the Bent County Soil <br />Conservation Board, <br /> <br />At Ule heart of OUt reseatch effort are activities aimed at gaUlering accurale and sufficient <br />information (data) to estimate state variables and parameters of the stream-shallow aquifer system of the <br />lowet Arkansas river valley. State variables of interest include water table depth, water table salinity, soil <br />salinity, and crop yields. Parameters include elements of system topology, boundary and initial conditions <br />on flow and salt transport, material ptoperties of the aquifer and river, local and areal sinks and sources of <br />flow and salts, and telated properties Ulat affect sinks and sources, <br /> <br />Preliminary Results <br /> <br />Water Table Depth and Salinity <br /> <br />About 73 observation wells distributed throughout the vaIIey region between Manzanola and the <br />Oteto-Bent county line (see attached map) are being monitored weekly for water table depth and salinity, <br />Exanlple contout maps of these variables (fot the measurements taken in early July) are attached. <br /> <br />About 30% of the wells show waler table depUls greatet than 10 ft below the ground surface. In <br />the remaining 70% of the wells, the water table depth fluctuates around an avetage of about 4.6 ft below <br />ground surface (see attached plots), It is estimated that the watet table depUI needs to be 6 to 7 ft below the <br />ground surface to ptevent advetse impacts from waterlogging and salinity, <br /> <br />The avernge measured salinity of the water table in the study region is about 4 dS/m (about 3200 <br /> <br />ppm), <br /> <br />Soil Salinity <br /> <br />The salinity of the soil (to a depth of about 3.3 ft) was measured in early June on 67 cliffetent <br />fields distributed over the region between Manzanola and Adobe Creek in western Bent county. On each <br />field, soil salinity (as electrical conductivity of saturnted extrac~ EC.) was measured at an average of 63 <br />locations (about5to lO locations pet acre), The avecage measured salinity exceeded the threshold level <br />(level above which Ctop yield reductions are expected) on about 70% of the fields (see attached plot). Soil <br />salinity wiII be measured again on these same fields in mid August. <br />