NorthPlatteBasinWaterSupplyandNeedsReport

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Section 3 Physical Environment of the North Platte Basin '.1111 and aquatic habitats. Habitat degradation, nutrient loading, soil erosion, and increased stormwater runoff are only a few examples of the concerns associated with rapid urbanization, particularly in the mountain recreational areas (Colorado Department of Public Health and Environment [CDPHE] 2000). Improving water quality and restoration and protection of water bodies in Colorado is occurring through programs such as the Total Maximum Daily Load (TMDL) process, Gold Medal fisheries establishment, instream flow programs, and federal and state listed threatened, endangered, and species of special concern. 3.2 North Platte Basin Physical Environment 3.2.1 Geography The North Platte Basin, shown in Figure 3-2, is located in north central Colorado in Jackson and a small portion of Larimer Counties. The basin covers an area of roughly 2,050 square miles. The population of Walden in Jackson County is 727 people (DOLA 2003). 3.2.2 Climate The average annual precipitation for the North Park Basin, which covers the majority of the North Platte Basin, is 19 inches. This average ranges from 11 inches in the valley center, near Walden, to more than 50 inches in the mountains that surround the valley (CGS 2003). Figure 3-3 shows color-fill contours for the average annual precipitation throughout the basin. 3.2.3 Topography The North Platte Basin in Colorado is bounded on the east by the Front Range, on the west by the Park Range, on the south by the Rabbit Ears Range, and on the north by the Colorado-Wyoming state line. The land surface elevation of the basin valley ranges between 8,000 and 9,000 feet (CGS 2003). 3.2.4 Land Use Land use in the North Platte Basin (USGS 1992) is shown in Figure 3-4 and summarized in Table 3-1. Almost half of the basin is forest (46 percent), located on the edges of the basin boundaries, followed by shrubland (24 percent), and grassland (17 percent). The shrubland is concentrated in the central portion of the basin. CONI 3-2 Grassland is typically located near the basin edges near the forested areas. Agricultural areas generally follow the basin's streams and rivers. Table 3-1 Land Cover Data for the North Platte Basin Basinwide Statewide Forest Shrubland Grassland Planted! Cultivated Open Water Barren Wetland Develqped TOTAL -.-. . 934' . 29,577 28.4% 481 16,883 16.2% 357 41,051 39.5% 222 13,737 13.2% 590 1,219 80 923 104,067 0.6% 1.2% 0.08% 0.9% 3.2.5 Surface Geology The mountain regions in the North Platte Basin are composed of Precambrian age metamorphic rocks that are extensively intruded by granitic igneous rocks. The North Park Basin is filled with sedimentary rock layers. The sedimentary layers range from flat-lying to steeply dipping folded and faulted structures (Pearl 197 4). 3.2.6 Surface Water The North Platte Basin drains the north-central portion of Colorado and consists of the North Platte River and two major tributaries: the Laramie River and Sand Creek. The North Fork, Grizzly Creek, Michigan River, Canadian River, and Illinois River are tributaries that flow into the North Platte River in Colorado. Sand Creek and the Laramie River flow northward out of Colorado and join the North Platte River in Wyoming. The North Platte River, Laramie River, and Sand Creek are shown in Figure 3-2. To monitor these streamflows, the USGS has gages in place in the North Platte Basin. Figure 3-5 shows the location of three of these streamflow gages. These gages are located on the North Platte River near Northgate, on the Laramie River near Glendevey, and on Sand Creek at the Colorado-Wyoming state line. They provide representative historical streamflows of the stream systems in the basin, as shown in Table 3-2, which also includes the length of record and the drainage area for each gage. Figure 3-5 also shows the locations of major diversions in the basin and segments with CWCB decreed instream flow rights. S:\1177\Basin Reports\North Platte\S3_North Platte.doc