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HomeMy WebLinkAboutDrainage Calculations • • ► 17j 4 RECEN D Drainage OCT 19 2000 __ tre DOCS Calculations cb 8 P PROJECT: STEWART PLACE Rangeline Road Carmel, Indiana PREPARED FOR: THOMPSON THRIFT DEVELOPMENT 1100 Spruce.Street Terre Haute, Indiana 47807 Phone: 812-235-5959 Fax: 812-235-8122 Date: October 19, 2000 Project Manager: James Peck, P.E. Designer: Aaron Hurt, E.I. Job Number: 200968 "777 Civil & Environmental Consultants, Inc. 2415 Directors Row, Suite E Indianapolis, IN 46241 Phone: 317-484-4280 Fax: 317-484-4284 Toll Free: 877-746-0749 . • PROJECT CRITERIA: ' DESIGN CRITERIA: Site Location: The project is located along Rangeline Road, directly east of the proposed Carmel City Center development. The northern property line of the site is located roughly 95'south of the south right-of-way line of Winona Drive on the east side of Rangeline Road. Survey Data: Lots 9, 10, and 11,in Newark addition, Clay Township, Hamilton County, Indiana. Site Narrative: The proposed development consists of a 9,000 square foot Building One that will occupy Sherwin Williams and additional tenants,as well as a 3,400 square foot Building Two that is designated for a commercial use. Three single story houses currently occupy the 1.291-acre site. Runoff from the site currently sheet drains to Rangeline Road where it empties into an existing curb inlet. From this inlet,an existing 12" R.C.P storm sewer carries the runoff further downstream. Adjoining Property Conditions: North Commercial South Commercial East .Residential \Vest Commercial (Future Carmel City Center) Existing Soil Information: Soil maps from the United States Department of Agriculture, Soil Conservation Service,identify Brookston (Br) soil on the Sherwin Williams site. Design Storm: The storm sewer system is designed to convey the 10-year storm event, while the proposed underground detention system is designed to restrict the 100-year post- developed runoff from the'site to the 10-year pre-developed outflow. Storm Sewer Design: Storm water runoff will be routed to three new storm inlets and further conveyed to an underground detention system that contains two storm inlets and three manholes. The underground detention system stores the 100-year 24-hour storm event and releases runoff into the existing curb inlet along Rangeline Road at the 10-year 24-hour pre-developed peak discharge. The rational method was used to size the proposed storm sewer system. A composite C value and a time of concentration were assumed for each storm inlet. Using Hamilton County IDS 2-foot contour information, it was determined that approximately 0.54-acres of offrite runoff enters the site. The 10-year 24-hour ofite runoff was routed through the site when determining both the existing 10-year release rate and proposed 100- year release rate. It was assumed that if these offrite areas are developed in the future at a higher intensity, they will be required to release runoff at the 10-year pre-developed rate. Using adICPR software, the resulting 10-year 24-hour existing runoff from the site was determined to be 1.84 cfs. i Underground Detention Design: The underground detention storage is provided by a network of twelve (12) 42" diameter corrugated metal pipe runs each 74'in length and two (2) 42" diameter header pipes each 61.25'in length. In order to provide additional storage capacity, a 42"diameter pipe run 52' in length was added to the last pipe run entering the system from the proposed parking lot. • Two inlets and three manholes are proposed for the parking lot above the underground detention system. One half the diameter or 21" of spacing is provided between pipe runs. A suitable stone base and backfill will be provided as specified by the manufacturer. In order to determine the proposed discharge from the system,a stage versus area relationship was determined and the proposed hydrograph was routed through the network using adICPR software. Using a 6"PVC pipe to outlet to the existing curb inlet along Rangeline Road,a proposed 100-year 24-hour peak discharge of 1.55 cfs was calculated,which is 16% less than the existing 10-year 24-hour peak discharge from the site. At this rate of discharge, water will reach a maximum stage of 839.29,which is approximately 2.5"less than the top of the pipes within the network. Therefore, the proposed underground detention system restricts the peak discharge to pre-developed levels without ponding water in the parking lot above. Developed Site Data: See the attached calculations. Summary: The proposed storm system has been sized to convey the 10-year storm event, without burdening downstream property owners. An underground network of 42" corrugated metal pipes will store and release runoff below the pre-developed 10-year 24- hour runoff rate. Adequate capacity and flow velocities exceeding 2.5 ft/sec were maintained. Ultimately, the proposed design effectively manages the storm water discharge from the site.