HomeMy WebLinkAboutDrainage Report 9-7-11IN
AMERICAN
STRUCTUR
INC.
201100921
Drainage Computations Summary
For
HealthSouth Rehabilitation Hospital
111 Street and Spring Mill Road
Carmel, Indiana 46032
Prepared By:
American Structurepoint, Inc.
7260 Shadeland Station
Indianapolis, Indiana 46256
Submitted by:
Bradley N. Schrage, PE, LEED AP
September 7, 2011
7260 Shadeland Station Indianapolis, IN 46256 -3957 TEL 317.547.5580 FAX 317.543.0270 wwvw.structurepoint.corn Q
AMERICAN STRUCTUREPOINT, INC.
DRAINAGE COMPUTATIONS SUMMARY
TABLE OF CONTENTS
Appendix A Existing Site Conditions
Appendix B Proposed Site Conditions
Appendix C Storm Sewer Design Spreadsheet
Appendix D Water Quality Calculations
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LOCATION
DESCRIPTION
DRAINAGE COMPUTATIONS SUMMARY
for
HealthSouth Rehabilitation Hospital
111 Street and Spring Mill Road
Carmel, Indiana 46032
The proposed project is located northeast of the intersection of 111 Street and Spring Mill Road along the
future Illinois Street in Carmel, Indiana. The site is not located within a special flood hazard zone as indicated
on the Flood Insurance Rate Map 18057CO208F for Hamilton County, Indiana, dated February 19, 2003. A
copy of the FIRM can be found in Appendix A.
The proposed project consists of the development of a 40 -bed (future expansion to 60 -bed) rehabilitation
hospital on approximately 6.3 acres within The Bridges PUD. A stormwater masterplan has been submitted
with the Mass Grading plan set for The Bridges which includes this 6.3 acre area.
EXISTING DRAINAGE
As a part of the Mass Grading Project, the HealthSouth site will be mass graded up to subgrade elevation. The
pond will also be constructed, but there will be no outlet structure under existing conditions. Temporary swales
will be provided around the site to drain the existing conditions towards the pond located in the southwest
corner of the property. The onsite pond is connected to an additional pond proposed by The Bridges Mass
Grading Project located just south of the property. The offsite pond will be constructed with an outlet structure
to limit the discharge to the south under 111 Street and into the Spring Mill Place Legal Drain.
PROPOSED DRAINAGE
The proposed project will consist of the proposed rehabilitation hospital located in the center of the site with a
parking lot surrounding the building. The site will drain via sheet and shallow concentrated flow towards the
proposed inlets which will convey the runoff to the southwest towards the pond constructed with The Bridges
Mass Grading Project. The entry drive located south of project site will also be collected by the storm sewer
system and discharged into the on -site pond. A copy of the drainage basin map can be found in Appendix B and
a copy of the drainage computations can be found in Appendix C. Due to site constraints, a variance is being
requested to allow a pond size of 0.31 acres at normal pool elevation in lieu of the required 0.5 acres. An outlet
structure will be provided as a part of the HealthSouth Project in order to restrict the release rate from the site.
The 10 -and 100 -year allowable release rates from the project at 0.1 and 0.3 cfs /acre are .63 cfs and 1.89 cfs,
respectively. The 10- and 100 -year proposed release rates from the HealthSouth Project are 0.71 and 1.13 cfs.
These release rates were achieved with a 7" orifice. Because the site was masterplanned as a part of the Mass
Grading Project, the allowable release rate was controlled at the downstream pond and is the cause of the 10-
year release rate from the HealthSouth Project exceeding the allowable release rate. The 100 -year elevation of
the onsite pond after the construction of the outlet structure is 842.84. These results are based on The Bridges
Mass Grading Project report dated September 9, 2011.
WATER QUALITY
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AMERICAN STRUCTUREPOINT, INC.
The proposed development utilizes both the provided Aquaswirl and the on -site pond to treat the runoff for
stormwater quality. The Aquaswirl removes debris and sediment from the runoff prior to entering the pond and
the pond allows for additional settling of suspended solids through longer on -site retention. The Aquaswirl was
sized to treat 5.36 cfs. The water quality volume required to be treated by the onsite pond is 0.34 acre -feet.
Approximately 1.51 acre -feet of storage are provided below the permanent water storage elevation. The
maximum depth of the pond is 8' and an area of approximately 0.17 acres is provided between 6 -18" in depth
for the littoral zone. The water quality volume and rate calculations can both be found in Appendix D.
CONCLUSIONS
The drainage from the proposed site has been designed according to the City of Carmel drainage standards. No
adverse impacts are anticipated to affect adjacent or downstream landowners.
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APPENDIX A
EXISTING SITE CONDITIONS
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