Modeling Residential Site Development with HydroCAD
HydroCAD case study submitted by McCrone, Inc.
Project Overview
Noble’s Pond is a residential community being developed by Regal Builders in
Kent County, Delaware. It is a medium density planned unit development
consisting of both single family and duplex dwellings. The project includes a
clubhouse and pool surrounded by 850 lots on approximately 293 acres. McCrone,
Inc. was retained to provide infrastructure design and guidance through the Kent
County permitting process for the multi-phase project. One of the key aspects of
the permitting process was stormwater management. The site drains to a
high-quality watercourse and the downstream effects of stormwater runoff were a
major concern to the community.
Pre-Development Hydrology
The site is primarily low-relief, poorly drained farmland including some
wooded wetlands and several ponds. The parcel is divided by streams and contains
many sumps. The stormwater management study point was identified at the
intersection of Fork Branch (the parcel’s boundary to the south) and one of its
unnamed tributaries, which runs through the parcel. Although McCrone, Inc. was
not required to study Fork Branch itself, they were required to assess and
manage water quality and quantity management at the study point. After meeting
with Kent Conservation District (KCD), a pre-development drainage area was
modeled in HydroCAD and the results were submitted. Using HydroCAD, McCrone,
Inc. modeled the farm fields, wooded areas, ditches and sumps. HydroCAD’s
modeling flexibility allowed McCrone, Inc. to effectively and efficiently manage
and model numerous subcatchments, as well as the complex, low-relief tailwater
conditions present on the site.
Post-Development Hydrology
Once the pre-development model was approved, a post-development model was
created, utilizing large stormwater facilities to provide quantity management.
During the design process, the Regional Planning Commission (RPC) requested
utilization of Green Technology Best Management Practices. McCrone, Inc.
identified locations where Green Technology BMP’s could be implemented while
minimizing impact to the existing layout. McCrone’s engineering team then
modeled the BMP’s and micro-practices with HydroCAD to achieve qualitative
stormwater management goals. McCrone engineers were able to quickly model the
BMP's, such as bioretention areas, bio-swales and micro-bioretention areas,
utilizing the different node types available in HydroCAD. After developing
working models for each BMP, the models were easily integrated into the previous
quantitative model and after minor adjustments, McCrone Inc. had a working model
that demonstrated both quantitative and qualitative compliance. Using HydroCAD
allowed McCrone engineers to make this major design change quickly and in a
cost-effective manner. This model and preliminary stormwater management report
was delivered to Kent County in October 2011.
December 2, 2011