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Estimating Monthly Hydrology for Ungaged Locations <br />Flow gages are not available for each location in the basin where it is necessary to develop <br />hydrology for the RGDSS Surface Water Model. However, these flows can be estimated by <br />using the "basin proration" capability of StateMod. This technique uses the baseflows (adjusted <br />to remove man-made effects) at gaged locations to estimate the baseflows at ungaged locations. <br />This technique prorates the gains between two gaged locations according to the respective area <br />and average annual precipitation tributary to each of the gaged and ungaged locations. StateMod <br />also allows the default proration calculations to be overridden with user specified data when <br />necessary. For example, an ungaged location can be prorated against a gage in a hydrologically <br />similar watershed, instead of the next downstream gage. More discussion of this important aspect <br />of the input hydrology for the Rio Grande Surface Water Model can be found in the <br />memorandum documenting Task 6.1 ("Define Drainage Areas, Develop Proration Factors and <br />Prepare Basin Map"). <br />Comments and Concerns <br />Occasionally it was necessary to create an *.stm (time series) input file for tstool, the result of a <br />data combination that was not possible using tstool commands or was the result of a regression <br />that was subsequently used in another data regression. This suggests some potential <br />enhancements to tstool that would aid in keeping the input data "data centered" and dynamic. <br />First would be a combination function, allowing certain periods of various gages to be "cut and <br />pasted" into a complete historical record for a single gage. Another enhancement would be to <br />allow two or more regression passes, allowing the results of one regression to be used in a <br />subsequent regression. <br />Attachments <br />1.Log file from tstool applications to develop model hydrology. <br />2. rg.rih: historic monthly streamflow file <br />C:Acdss\Task6-6.doc Prepare River System Files March 8, 2000 -Page 11 of 11 <br />