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Computer estimates of natural recharge from soil moisture data, High Plains of Colorado




Longenbaugh, R. A., (Robert A.), author
Krishnamurthi, Narayanaswamy, author
Environmental Resources Center, Colorado State University, publisher

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The research described briefly in this completion report has shown that transient soil moisture data observed at vertical positions at one station can be used as descriptors of natural groundwater recharge to evaluate its time distribution at that station. Hydraulic properties of the soil and initial and boundary conditions must be known before applying the mathematical model developed in this study to other locations. The model developed in this study assumed that the moisture content of unsaturated soil below the zone of influence of evapotranspiration varies in the linear range of the soil water characteristic curve. The parameters of the model characterize the hydraulic properties of the soil and their spatial variability. They were estimated by a linear statistical model. The mathematical model was solved by a Finite-Difference technique adopting the Crank-Nicholson scheme. The model was verified with an analytical solution and the agreement for the case of homogeneous soil was very good. Field data collected during a drainage cycle were used to verify the model for non-homogeneous soil. The verification was also found to be satisfactory in the latter case. The model was then applied to estimate recharge rates from data collected by the USGS and ARS at the Great Plains Field Experiment Station near Akron, Colorado. Estimated monthly recharge rates varied from a low of 0.02 inches to a high of 1.42 inches. Comparison of the Akron recharge estimates with other data indicates the values were acceptable. An average annual recharge of 4 inches was computed for the Akron site. This result was compatible with the observed rise in the local water table of 3 feet during the same time period.


Submitted to Office of Water Research Technology, U.S. Department of Interior by R. A. Longenbaugh and N. Krishnamurthi.
July 1975.

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Groundwater flow -- Mathematical models
Groundwater flow -- Data processing
Soil moisture
Soils -- Colorado
Groundwater flow -- Colorado


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