HomeMy WebLinkAboutDrainage ReportDRAINAGE REPORT
ITT BUILDING EXPANSION
DRAINAGE REPORT
HAMILTON CROSSING
CARMEL, INDIANA
February 19, 2010
TABLE OF CONTENTS
DRAINAGE SUMMARY SECTION 1
EXISTING CONDITIONS FROM MASTER DRAINAGE PLAN SECTION 2
DEVELOPED CONDITIONS STORM SEWER DESIGN SECTION 3
WATER QUALITY SECTION 4
Woolpert ITT Building Expansion
February 19, 2010 Hamilton Crossing 1
SECTION 1: DRAINAGE SUMMARY
Existing Conditions
The existing site is located in the Hamilton Crossing office park (Building #5) near the southwest
corner of U.S. 31 and 131 Street. The site is part of the Meridian Corners master planned
development, now known as Hamilton Crossing, which was approved in 1989. The existing
office building and parking lot are located within a 3.93 -acre drainage area that drains to the
southwest corner of the site, to an existing storm sewer. This drainage area is part of the overall
basin S -7 in the Meridian Corners master drainage plan, which was designed for a post
developed curve number of 94. The existing system drains into an existing detention pond
southwest of the project site, which was sized in the Master Plan to accommodate full
development of the site. See pertinent portions of Meridian Corners Master Plan included in
Section 2.
The existing parking lot and building rooftop drain through on -site storm sewer, which connects
to Structure 12 at the southwest corner of the site, where it then leaves the site and enters the
overall Hamilton Crossing storm sewer. The open area south of the existing building and
parking lot makes up a 1.07 -acre sub -basin that drains to a swale along the south of the site,
which drains west to a storm pipe also connected to Structure 12.
According to the FEMA Flood Boundary and Floodway Map, Community Panel 18057CO206F,
the site lies outside of the 100 -year floodplain or floodway. The soil types for this site are Crosby
Silt Loam and Brookston Silty Clay Loam.
Developed Conditions
Wool pert ITT Building Expansion
February 19, 2010 Hamilton Crossing
Carmel, Indiana
The proposed development consists of a 15,600 square foot (footprint) addition to the existing
building. Along with the building, the developed conditions will include grass, landscaping, and
rain gardens for water quality purposes. The existing parking lot and building rooftop will
continue to drain through existing on -site storm sewer to Structure 12. The proposed building
addition and other site improvements are all located within the 1.07 -acre south sub basin.
Runoff from the roof of the building addition, along with all of the disturbed area, will be
directed to the swale along the south of the site, which will be converted into a rain garden,
before discharging to Structure 12.
Since the proposed CN value for the site is less than the developed CN required in the master
plan, additional detention is not required for this development. The proposed rain garden,
however, will provide a level of detention for stormwater runoff from the proposed improvement
area.
The rain garden was analyzed using the Advanced Interconnected Channel and Pond Routing
(AdICPR) program version 3.02. The outlet structure will be a 24" beehive casting atop a
manhole structure. The casting elevation has been designed to force the water quality volume to
infiltrate through a sand filter bed and a perforated underdrain. Runoff from the site above and
beyond the water quality volume will drain into the beehive inlet, through the storm sewer outlet.
The 10 -year 100 -year, 24 -hour stonn events were analyzed in the AdICPR model for sizing
and routing purposes. Support Calculations are included in Section 3.
In the case of backup to the outlet pipe, the emergency overflow will occur west of the rain
garden outlet structure. This condition assumes the storm sewer outlet is completely blocked and
that all on -site depressional storage is full of water. The overflow will be directed west to
Hamilton Crossing Blvd, and will not impact the adjacent buildings or major public roads.
As stated previously, the post construction Water Quality will be handled through the use of the
rain garden along the south of the site, which provides the necessary water quality storage
volume for the contributing drainage area. This water quality basin will function like a
bioretention facility in that it will use the underdrain wrapped in filter fabric and in a sand bed to
filter the first flush from most rain events. This type of system will remove the required 80%
Total Suspended Solids and fine sediments from the storm water flow. The addition of plantings
in the rain garden adds the extra benefit of removing dissolved heavy metals and phosphorus,
which is not yet required by the City of Carmel Technical Standards. In addition to the rain
garden, an Aqua -Swirl unit will be used as secondary treatment of the stormwater. Water quality
calculations can be found in Section 4 of this report.
Water Quality Summary of Results:
WQ WQ Water Quality 100 -Year 10 -Year
Volume Volume Elevation Elevation Elevation
Required provided
(ac -ft.) (ac -ft.)
Water Quality
Basin (Rain
Garden)
Conclusion
0.033 0.040 865.00 865.44 865.27
The ITT Building Expansion meets the drainage standards of the City of Carmel and for the
Meridian Corners Master Drainage Plan, and incorporates innovative water quality design
solutions. The proposed CN for the development is less than the developed CN identified in the
Meridian Corners Master Plan, therefore, no adverse impacts related to storm water drainage and
quality are anticipated from this development.
Woolpert ITT Building Expansion
February 19, 2010 Hamilton Crossing
Carmel, Indiana