Page 6 - March-April2020 Vol37 No7

GERMANTOWN
Stormwater Master Plan in Action
As cities grow, population is not
the only statistic that changes. Local
governments are tasked to maintain a
variety of assets, from roadway systems
to natural resources and everything in
between.
The city of Germantown, a suburb of
Memphis, saw explosive growth between
1970 and 2000. The surge in population
leveled off around 2000, but the influx of
people and limited land resulted in the
need for new types of developments.
Zero-lot-line and mixed-use buildings,
often called “infill developments,” are
designed to accommodate a large number
of people in a small footprint. Infill
developments often replace traditional
quarter-acre-lot residential subdivisions
and create more impervious area per
acre of land in the City, which affects the In order to determine which assets to
absorption of rainwater.
The large volume of added impervious
area increased stress on Germantown’s
aging stormwater infrastructure, because
the system was initially designed with
much different criteria in mind. This
added stress can worsen existing trouble
areas or create flooding in areas which
6 TPW March/April 2020
never previously had issues. The City was
aware of the potential issues, and in 2016
decided to establish a plan to handle these and respond to emergent needs as they
development trends and implement a
strategy to prioritize stormwater drainage
system improvement projects.
Typical for American cities,
Germantown’s Capital Improvement Plan
(CIP) is essential to the municipality’s
ability to prioritize public projects.
With great forethought, Germantown
allocated resources in their current CIP
toward improving the stormwater system.
The City understood it was crucial to
strategize, identify and organize flood
mitigation alternatives.
The budget allocated in the CIP did
not allow flood mitigation efforts to be
completed for the entire City at once.
prioritize, the City had to take inventory
of the current system and identify the
most immediate concerns.
Germantown teamed with Barge Design
Solutions, Inc. to prepare a stormwater
master plan. Barge’s inventory of
Germantown’s systems has helped the City
prioritize the numerous projects outlined
By Trevor A. Cropp, P.E.
in the CIP, validate the necessity of a
stormwater strategy for the City’s growth,
arise.
Taking Inventory of Current Assets
An inventory of this scale begins
with an understanding of the already-
collected data. The then-current
stormwater infrastructure data included
outdated, scanned record drawings from
previous construction projects. Without
modernized systems, this preliminary
data collection phase was bound to be an
arduous and expensive process.
To bring the City’s systems up to date
and facilitate more accurate reporting,
Barge created and configured an ArcGIS
Online Map. This technology utilizes
mobile tablets and phones to collect
photos, condition assessments, measure
downs and field comments, which are all
georeferenced.
The process of data collection is
streamlined in an app using dropdowns,
toggle buttons and check-blocks. All the
data can be viewed and edited by the City
on a webpage, which enables managers
Left: A map showing the drainage basins.
Above: The new technology allowed the
City to take inventory of their entire
network of stormwater assets. This is a
concrete lined tributary to the Wolf River.
Near right: A screenshot of the PCSWMM
model showing the network of stormwater
system assets.
Far right: Screenshot of the PCSWMM
model showing the density of
developments within City limits.