Upper Los Pinos Water Quality Report

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Vegetation of the study area is a combination of ponderosa pine and spruce-fir forests, aspen stands, bare rock and d>v grasses, and willo~~- and ~-et-grass bogs (U.S. Department of Agriculture and Colorado Department of Natural Resources, 1979). Mimed in with these vegetation types at to«-er altitudes are pinyon-juniper woodland, mountain shrub, sagebrush steppe, and grassland settings. The upper Los Pinos River watershed has two main branches upstream from Vallecito Reservoir-- Vallecito Creels and Los Pinos River. The Los Pinos River is a south«, and flowing tributai~~ of the San Juan River. which is a major tributan- to the Colorado River. Streamflow discharges can vary- substantially: about 80 percent of the annual runoff is derived from snowmelt which occurs during May, June, and Jule of each year. For eiample, discharges in Vallecito Creels upstream from the reservoir can range from about 7 ft~ /sec during the low-flow period of late summer to more than 1,000 ft~/sec during snowmelt runoff of May-July (fig. 3). Streamflow discharges in Los Pinos River also vai-~- «itli sno«-melt runoff: however, there are no long-term streamflow records for Los Pinos River upstream from Vallecito Reservoir. VALLECITO CREEK UPSTREAM FROM VALLECITO RESERVOIR AT USGS STREAMFLOW GAGING STATION 0 3.500 z as° O 40° DROUGHT OF 2002 w 3,000 3~ ~ 3°° a z,eao Z~ F Z°° W ~° LL z aao +°° U s° m U 1 SOO ° Oct Nov Oec Jan Feb Mar Apr May Jun Jul Aug Sep z ~ I kihd16d61i,iIh~IlVll~~l~~ld~l~~l Figure 3. Streamllow discharges in Vallecito Creek Iar water years 1962-2003. The effects of droughts during 1977 and 2002 can be seen by the streamflow data shown in figure 3. Sno~~znelt nmoff peals discharges are t<-picalh- about 1,000 to 1,300 ft3/sec: however, during June 1977 and May 2002, the peals strea~nflows reached a magnum discharge of 308 and 171 ft~/sec, respectively. Some of the largest discharges originate from lame, frontal- type rainstorms approaching from the southwest during August through October. The 100- and ~00- yearfloods predicted for Vallecito Creels at the USGS gaging station are 8,300 and 21,00 ft3/sec, respec- tively_ (U.S. Army Corps of Engineers, 1976). During the period June 9 to July 15, 2002, the Missionai~- Ridge wildfire burned 70,48 acres in the forested and developed lands northeast of Durango, Colorado. Of this acreage 31 percent, or 22,42 acres was considered severely burned with the majority of this area on steep slopes at the head of small tribu- taries. The Burned Area Emergency Rehabilitation (BAER) team and the La Plata County Office of Emer- gency Response recognized the potential for flooding and debris floe s from these areas. About 8,000 acres of the Missionan~ Ridge wildfire burned in the upper Los Pinos River watershed. During the summer of 2003, the Bear Creels wildfire broke out in the upper Vallecito Creek watershed al~d burned about 1,00 acres. These «-ildfires are a natural part of a forest ecosystem: however, there are impacts from «ildfires that affect communities and water resources. METHODS OF INVESTIGATION Literature Review Reports describing the natural and ~~ ater resources of the upper Los Pinos River watershed date to the 1970's when the water and land resources were beuig surveyed by State and Federal governments (Soil Conservation Service, 1974), and the Wemi- nuche Wilderness was being established (U.S. Depart- ment of Agriculture and Colorado Department of Natural Resources, 1979). Reports are available describing the general baseline water-quality condi- tions of the State of Colorado and the San Juan River Basin (Colorado Department of Public Health, 1987: Colorado Water Quality Control Division, 1989): ho~~-ever, the upper Los Puios River watershed is only briefly mentioned in these reports. Flood hazard investigations for the Vallecito Reservoir area were conducted at the request of the Animas Regional Plan- nuig Commission, the Colorado Land Use Commis- sion, and the Colorado Water Conservation Board (U.S. Arny Corps of Engineers, 1976). Reports are available regarding Vallecito Reser- voir and the Pine River Irrigation Project. An investi- gation was done in 1948 that summarizes the fish and ~' ~ SouthwestHydro-Logic 5