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The suggested improvements consist of installation of larger culverts beneath the road and raising the road surface approxi- mately 2 feet. The result will be to significantly reduce the frequency of inundation of the golf course and the condition of flow across the road surface, while slightly increasing the area subject to flooding from a 100 year storm occurrence. These improvements are imperative to the overall functioning of the drainage system. Since the entrance road serves as a major deten- tion pond with significant flood routing effects, an agreement should be obtained with Green Gables Country Club to assure the continued existence of the entrance road. The proposed facilities will totally collect dll runoff from storms up to the 20 year frequency for Main Sanderson Gulch. Greater storms will flow across Jewell Ave. and into the shopping center area. The recommended improvements suggest final grading of Jewell Ave. to restrict this street overtopping along the align- ment of the proposed improvement. The majority of flow would con- tinue southeasterly across the parKing area toward Wadsworth Blvd. Portions, however, would be diverted directly to the south into the sump area behind the shopping center building. Local inflow from the historic alignment of South Sanderson Gulch would also enter the sump area. To prevent damage to the main shopping center complex during major storm occurrences, the road along the south end of the main complex should be lowered 6" to l' to allow accumulated waters to escape to the east. The existing culverts beneath the entrance road are minipulated in such a way that normal low flows by-pass the Shwayder Pond. This is accomplished by means of a 42" reinforced concrete pipe laid around the periphery of the pond. The proposed im- orovements would permit the continuance of this practice. . . Drawing No, S-lO The design approach utilized On Sheet 8-10 is essentially constant from one end of the sheet to the other. Five existing street crossings of the gulch now exist. Each crossing is inadequate and will be replaced by new culverts. the recommended inst~llations consist of double 72" x 44" corrugated metal pipe culverts with head wall entrances. These culverts will pass the design 10 year runoff without inundation of the street surface. Flow in excess of the 10 year runoff will continue across the street surfaces. A typical cross section is indicated illustrating recommended de- sign for the cross section of Jewell Ave. and the intersecting streets. the cross section will maintain the 100 year storm street overflow to the vicinity of the drainage channel ~nd allow Jewell Avo. to remain 0gen for traffic. Drawinq No. S-9 EaST of Wadsworth Blvd. the gulch is flood plain zoncd across the Green Gables Country Club Golf Course. The improvements from Wadsworth Blvd. to Jewell Ave. must be viewed as a unit sinoe the entire system must function together. An existing 48" reinforced concrete pipe has been installed across the shopping center parking lot. Original plans for the area indicated that low flcws would be carried by the 48" reinforced concrete pipe while major flows would flow overland across the ditch portion of the parking lot. The basic concept was rela- tively sound; however, construction of a filling station in pOI"- tions of the swale, together with the difficulties encountered at West Jewell Ave. and Wadsworth Blvd., render the plan unaccept- able. In addition, the pipe capacity cannot be reached with the existing inlet ccnditions. The channel improvements consist of grading, grassing and installa- tion of drop structures in a channel cross section with 3:1 side slopes. The improved channel will be located in a 50 foot right- of-~ay adjacent to the proposed lOO foot right-of-way of Jewell AVe. The recommended improvements consist of installing a parallel- ing 54" reinforced concrete pipe across the shopping center parking lot and installing three new 38" by 60" horizontal elliptical reinforced concrete pipes beneath wadsworth Blvd. The proposed conduits beneath Wadsworth Blvd. are sufficient to carry a 20 year storm runoff frOM the entire basin above Wads- wQrth Blvd., whil~ th~ cnndults across the shopping center p~rk- ing lot are sufficiently sized to carry the 20 year storm capacity from the gulch above Jewell Ave. Special measures a~e indicated to assure that the full capacity of the pipes may be developed by uses of special entrances and reducing sections. If develOpment of the area necessitates the installation of a covered conduit in reaches presently indicated as open channel, the conduit should be designed to carry the lO year discharge indicated on the design sheet. Grading of areas adjacent to Jewell Ave. should coincide with the typioal crossing detail indicatcd on the master plan sheet to allow runoff in excess of the 10 year to continue along the side of the road without interferring with traffic on clAW...ll Avp-, Drawing No. S-ll The be~ On Jewell Park Pond should be raised to elevation to contain the 100 year storm runoff without overtopping, 5576.5 A ne'" -98- -~;J-