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,,1'\" '<13 Ii" (. ~. The major source of water in northwestern Colorado is the high-elevation mountains east and south of the Yampa River valley. Water from these high mountain areas flows through the more arid valley. In the past, streamflow- gaging stations were operated on tributaries that drain the high mountain areas and on the main stem of the -Yampa River. Streamflow gaging of tribu- taries in the more arid valley virtually was ignored. - Coal mining in the southern Yampa River basin generally is concentrated in small drainage basins in the arid valley where there are few streamflow- gaging stations. Mining companies and government agencies have been concerned about the effects of mining on the water resources, and they also have been concerned about the availability of water for mining-related activities and other uses. However, because the tributaries in these small drainage basins generally were ungaged and because streamflow characteristics can be derived only after some years of measuring streamflow at appropriate sites, _a streamflow-gaging program for the small drainage basins was needed to identify these characteristics. Measurements made in one drainage basin may be useful in answering questions about the water resource in that specific basin, but it is not known whether these data would be useful or appropriate for other similar drainage basins that are several miles away and for which no stream- flow measurements are available. Therefore, a technique was needed to assess the water- resources in gaged drainage basins and to provide a mechanism to transfer these data to ungaged drainage basins. These capabilities are avail- able in the Precipitation~Runoff Modeling System (PRMS) (Leaves ley and others, 1983). This modeling system enables an evaluation of the magnitude and variability of the components of the water balance in the drainage basins - monitored and provides some mechanism for transfer of hydrologic data. This study was done in cooperation with the U.S. Bureau of Land Manage- ment, which manages much of the Federal land and coal reserves in the study area. The water-resource information is needed so that the U.S. Bureau of Land Management can assess the effects of coal mining in the small drainage basins. Therefore, the study was done to: (1) Determine drainage basin characteristics and calibrate PRMS for simulating streamflow in drainage basins monitored in the program, and (2) assess the transferability of model parameters within the southern Yampa River basin. The purposes of this report are to: 1. Describe the methods used in the study. 2. Describe the drainage basins monitored. 3. Describe the model results for these drainage basins. 4. Describe the applicability of the model to additional monitored basins and to assess transferability of model parameters. Three drainage basins were monitored in each of three hydrologic regions in the study area. Two drainage basins in each region were used to calibrate and verify PRMS and to assess hydrologic variability. The third drainage basin in each region was not calibrated but was used to test the transfer- ability of model parameters in the particular region. For all of the drainage basins except one, period of record used for calibration and verification included water years 1976-81. 2 ~.,-.' ,~,... ~:~f~ ~:~, [~~ ~~~~ ::::q; ~~% r~~ ;,;~.~.: ~~~ .~ ~~f ~t~ ~';y,:. ttf~ ~;:('>...:~ ~Mi;: r....~ ~~ ....'.. ~~::~~ ii.~ ~:;:~1! ~~~i{ ~~~ ;t.~~:: .~' ,>-:':r. .,,~'<... "'.-. i....:.. .;.: '.,,;.,;'; ;-:'..:' ; ""'~.~