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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />11 <br />I <br />I <br />'I <br />I <br />I <br />I <br />I <br />II <br />!I <br />il <br /> <br />IV. STUDY AREA DESCRIPTION <br /> <br />Location <br />The Town of San Luis is the County Seat of Costilla County, Colorado and lies within the <br />southeastern part of the San Luis Valley. The town is approximately 220 miles southwest <br />of Denver, and is about 15 miles north of the Colorado-New Mexico state border. It is <br />the oldest town in Colorado and was established in 1851. San Luis is located at about 37 <br />degrees, 12 minutes N. latitude, and 105 degrees, 25 minutes W. longitude. A location <br />map for San Luis is shown in Figure 1. <br /> <br />Site Characteristics <br />San Luis lies just to the north of Culebra Creek, which is tributary to the Rio Grande. <br />The elevations within San Luis range from approximately 7,950 feet to 8,000 feet (msl). <br />The town is in the San Luis valley which is a high mountain valley situated to the east of <br />the San Juan Mountains, and to the west of the Culebra and Sangre de Cristo Ranges. <br />The area surrounding the town is undeveloped and consists of irrigated hay, range, and <br />forest lands. A vicinity map for San Luis is shown in Figure 2 and depicts the general <br />topography and drainage courses in the study area <br /> <br />Site Specific Drainage Problems <br />The following information regarding site specific drainage problems in San Luis was <br />provided in the form of a trip report by William Wittwer of the Natural Resource <br />Conservation Service. Pertinent information from the trip report has been edited and <br />summarized by the CWCB in this section. <br /> <br />The Town of San Luis is constructed on the alluvial fan of an ephemeral stream called <br />Rito Seco and, as such, the town is subject to flooding from it. Fear of flooding as a <br />result of heavy spring snow pack led to the construction of a flood control dike around the <br />east side of town with Corps of Engineers emergency funds. With the construction of this <br />dike, the flow of water into the Rito Seco channel was restricted, and the channel has now <br />adjusted to the smaller flows. The resulting stream system is a smaller channel with a <br />higher water table than that which previously existed. <br /> <br />The water table problems of current concem are south of the previous drainage project and <br />are in the main part of town. The exact source of the problem in this area can only be <br />determined by completing a drainage survey of the area However, the drainage <br />investigation conducted during the spring of 1987 indicated that the general flow of ground <br />water was from the north. The investigation also found numerous old channels of the Rito <br />Seco meandering through the town. These old channels were filled with coarse sand and <br />gravel which operate as water conduits throughout the town. Houses constructed on Of near <br />these old buried channels are the most effected by the water table. Remnants of old surface <br />channels can be seen throughout the town, and all have been fJI1ed in places as houses were <br />constructed. The filling of these old surface channels has adversely affected the natural <br />surface drainage. In some areas, ponding can still occur in these old channel remnants, <br />which contributes to the water table problems. These areas should be filled or otherwise <br /> <br />3 <br />