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I I I I I I I I I I I I I I I I I I I 2 It is estimated that an average annual benefit of approximately $l,26l,000 would result from the reduction of flood damages. The recommended Master Plan for the entire basin has a benefit-cost ratio of l.5l. Benefit-cost analyses were made for eight differ- ent reaches of the studied channels, yielding benefit cost ratios ranging from 0.06 to 2.92. These benefit-cost ratios illustrate that facilities in certain reaches are more cost effective than those in other reaches. crete trickle channel, reshaped sideslopes with natural grass, and maintenance access roadways. 2. On Dry Gulch between Harlan Street and Wadsworth Boule- vard, the Master Plan recommends larger capacity culverts at street crossings, with open channels in between. 3. On Dry Gulch from Wadsworth Boulevard to Carr Street, a storm sewer system is proposed. 4. A detention storage pond is proposed on Dry Gulch west of Carr Street, to be incorporated into the planned park. 5. Between the detention pond and Garrison Street, the Master Plan recommends open channel crossings with im- proved culverts at street crossings. 6. From Garrison Street to the upstream end of Dry Gulch at 2uail Street, a storm sewer system is recommended, except west of Kipling Street, where a short segment of open channel is proposed. 7. A storm sewer system is proposed for the entire length of North Dry Gulch, with the exception of the block between Vance Street and Wadsworth Boulevard, where an open channel is planned. The Master Plan The Master Plan for Dry Gulch and North Dry Gulch consists essentially of proposed facilities to convey the 10-year flood without causing damage to structures, inconvenience to motorists, or personal injury. All of the proposed facilities are illus- trated on the Major Drainageway Planning Sheets of this report. In the event of a lOO-year flood, a majority of the flow would be conveyed by the proposed facilities, but a portion of the flood would proceed overland, causing damage and inconvenience in certain areas. The anticipated limits of flooding in a 100- year flood before and after construction of facilities are shown on the Major Drainageway Planning sheets. In addition, the water surface profile or the hydraulic grade line during a lO-year flow are illustrated. The principal elements of the proposed plan are described below: l. From the confluence of Dry Gulch and Lakewood Gulch to Harlan Street, an open channel is proposed with a con- The following Sections of this report present, in detail, the proposed facilities, the estimated costs, and the anticipated benefits. Additional information regarding the preliminary de- sign of this report is available in the office of the Urban Drainage and Flood Control District, and in References land 2.