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I 'I I I I I I I I I I I I I I I I I I I One man-made feature affecting drainage patterns is the railroad em- bankments. The railroad serves as a boundary that has altered historic drainage patterns, and has indirectly affected development in the area. One railroad was built on a berm from West Avenue to the northwest. Current drainage patterns from the northwest can be identified in Figure 1. Other man-made features affecting drainage patterns include state highways and local roads that are elevated above the surrounding ground. They either block drainage or change the flow pattern of drain- age. In northwestern Alamosa, the general trend of the drainage, based on the natural contours in the area, blocks the flow to the southeast. However, State Highway 17 for example, blocks the flow to the south- east and directs drainage towards the south. U.S. Highway 160 blocks the drainage from the north and, coupled with recent development, has directed runoff to the west. U.S. Highway 285, south of Main Street, has effectively blocked drain- age from the west from continuing east to the Rio Grande River, caus- ing several ponding areas. A portion of the Hickory-Jackson irriga- tion ditch is elevated above the surrounding ground and blocks drain- age to the south of the city. Natural features in the area also affect natural drainage patterns such as the many natural sumps (depressions or pits where water accu- mulates) which have no outlet. Some development has occurred in these areas, resulting in localized flooding because of no drainage. As noted on Figure 1, the natural topography is nearly flat. For example, some areas have only a five-foot drop in elevation within a mile-and- a-half distance. Development has not followed typical standards for grading lots, streets, etc., all resulting in inadequate drainage. and localized flooding. Table 1 summarizes many of the physical features contributing to the drainage problems of the area. ~-