There was a 6 inch topsoil rule in Iowa. The DNR rescinded the rule once
there was a change in administration. Clive (a city in metro Des Moines)
has a 6 inch topsoil rule. Ms Conrad, engineer, said there was a lot of
"push back" on this ordnance. They educated the city council that topsoil
reduces flow rates or there is a slow release of water (which impacts
flooding) and other benefits.

Here is a summary of their presentation.

In 2016, the City of Clive adopted the Walnut Creek Watershed Management
Authority’s master plan, which aimed to restore water and soil health
within the watershed. In further support, Clive created a progressive
post-construction stormwater management ordinance in 2016 and revised the
Stormwater Management Manual again in 2019.

In March of 2019, the City approved a Sponsored Research Agreement with
Iowa State University. Researchers at ISU and Auburn University are
modeling and site-monitoring two paralleled developments to understand and
demonstrate the extent of benefits from the ordinance on the Walnut Creek
Watershed.

The first development, Angel Park, was platted in 2012, prior to the
adoption of the ordinance. The neighborhood is 70 acres and approximately
80% built out. Monitoring in this area encompasses 56 acres and is being
conducted on a dry detention basin which discharges to Walnut Creek.
Conversely, Shadow Creek was the first major development after the adoption
of the ordinance. The expected completion of the 91 acre neighborhood is
2023, with 67.2 of these acres are being monitored for this study. The
development was designed to meet the requirements of this ordinance, which
follows the principles of the unified sizing criteria and includes a
wet-detention pond, soil quality restoration, and bioretention cells to
encourage water infiltration.

Initial field instrumentation was completed in August 2019. Monitoring is
ongoing as the Shadow Creek development approaches full build out. Results
from monitoring will be compared to hydrologic models to determine
effectiveness of the Post-Construction Stormwater Management Practices.
Pending results, this project aims to demonstrate the expected benefits of
the City of Clive’s progressive ordinance on Walnut Creek, which will set
the precedent and hopefully lead to a unified approach to stormwater
management in surrounding communities.

Rachel Conrad will be presenting on the City’s ordinance and manual and
Jaime Schussler will be presenting on the monitoring results so far.

-- 

*Debbie Neustadt *


*Des Moines, Iowa*

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