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I I I I I I I I I I I I I I I I I I I - CHANNEL IMPROVEMENTS - residential with strips of commercial development along Federal and Sheridan Boulevards. During the period from 1975 through 1978, many of the improvements proposed in the major drainageway planning study (Reference 1) were designed and constructed. The design discharge for these improve- ments was generally the following: 100-year frequency design for open channels along Sanderson Gulch 10-year frequency design for culverts on both channels 10-year frequency design for open channels along North Sanderson Gulch The basin above Sheridan has been built up over the past 20 years. This area is primarily single family residential with small com- mercial areas, particularly along Wadsworth Boulevard. The upper basin also continues to have a considerable amount of open space primarily along Sanderson Gulch between Sheridan and Wadsworth Boulevards. Several of the old irrigation reservoirs remain in these open space areas providing natural detention basins which dampen the effects of high flows as they move downstream. On Sanderson Gulch, an improved grasslined channel extends from the South Platte River to Federal Boulevard. Culverts were improved at Lipan Street, Arkansas Avenue and Zuni Street. Only minor im- provements were completed from Federal Boulevard to Sheridan Boule- vard consisting primarily of small drop structures. The lower Sanderson Gulch basin below Sheridan Boulevard has reached full development. The upper basin is also rapidly approaching this condition. In a previous report, "Major Drainage- way Planning, Sanderson Gulch/Weir Gulch," 1972 (Reference 1), basin development was reported to be 83% complete. Part of the remaining 17% includes park and open space areas that are likely to remain as such. Improvements were made to the existing Bit-O-Sea Reservoir imme- diately above Sheridan Boulevard. The earth embankment was raised and protected to increase storage, and the spillway was improved to increase capacity for discharge of the 100-year event. Development within the basin was pursued in early years without regard for the natural drainageways. In several sub-basins of Sanderson Gulch, the natural stream channel was completed obliterated. North Sanderson Gulch is the only significant tributary channel to Sanderson Gulch that remains today. From Wadsworth Avenue to Jewell Avenue, improved culvert facilities were constructed under the King Soopers' parking lot. Parallel to Jewell Avenue, from Allison Street to Jewell Park Pond, an improved grasslined channel has 100-year capacity. New culverts were in- stalled along this reach at Allison, Ammons, Balsam, Carr and Cody Streets, and improvements were made to the Jewell Park Pond. Development along both Sanderson Gulch and North Sanderson Gulch has encroached upon floodprone areas. In 1972, major drainageway planning (Reference 1) along these channels identified these floodprone areas and the inadequacy of the existing drainageway. The Urban Drainage and Flood Control District, together with the City of Denver and the City of Lakewood, has followed through with construction of many of the recommended improvements which has greatly reduced the flood potential within the basin. Further channel modifications increased capacity to contain the 100-year event from Garrison Street to Kendrick Reservoir. A new culvert was constructed at Garrison. Kendrick Reservoir embank- ment and spillway facilities were modified to insure safety and to increase the capacity of the reservoir system. Channel improvements on North Sanderson Gulch begin a short dis- tance downstream of Pierce Street and extend upstream to Florida (2)