Runoff Control from Development
Drainage
Design and Erosion Control Manual
When land is developed, much of the spongy ground that used to soak up
rainwater is replaced with impervious surfaces such as roads, roofs and
driveways. Thurston county and its cities require developers to manage
the rainwater runoff that flows off of these hard surfaces.
Those requirements are spelled out in a document called the
Drainage Design and Erosion Control Manual.
Developers use a variety of methods to manage stormwater runoff --
swales, ditches and stormwater ponds among them. Simply put, the goal is
to send rainwater into the ground or nearby streams at the speed and
volume that best mimics how the water would have dispersed naturally had
the development not been built.
In virtually all cases, the Drainage Design and Erosion Control Manual requires builders to submit a drainage plan
when applying for building permits. The drainage plan must clearly show
safeguards to prevent erosion, and how the development will direct,
store, and dispose of stormwater runoff.
The manual also requires developers to manage the stormwater runoff
at the construction site.
An updated version of
the Drainage Design and Erosion Control Manual took effect November
16, 2009. The new version complements the state
Department of Ecology's
Stormwater Management Manual for Western Washington.
Stormwater
Site Inspections
Thurston County
requires thorough on-site inspections of stormwater facilities before,
and after they're built. The requirements are spelled out in the
Drainage Design and Erosion Control Manual described above.
Stormwater
Pond Maintenance Requirements
Thurston County Ordinance 15.05 requires all property owners to
maintain their stormwater facilities according to maintenance plans and
schedules filed with the county. These plans are signed by the developer
and submitted to Thurston County with the final plat or commercial
permit.
In the case of
housing developments, developers are held responsible for maintaining
stormwater facilities for the first two years. Then, the responsibility
is transferred to a homeowner's association.
Assistance
for Homeowners
Thurston County and
its cities offer free workshops to
teach
residents how to maintain and inspect neighborhood stormwater ponds and
meet reporting requirements. Thurston County also offers free
technical assistance
for ratepayers who are experiencing drainage problems.
Construction
of Stormwater Facilities
Thurston County constructs
stormwater facilities to help reduce flooding and
erosion in older neighborhoods that were built before
development rules were in effect.
For information call
754-4681 or route a message through
wwm-webmaster@co.thurston.wa.us
Last updated:
01/28/10 06:27 PM
