Storm Water Design Criteria Manual — January 2016
Chapter 2 | Page | 2.3
2.6 TECHNICAL CRITERIA
The storm drainage planning and design should follow the criteria within this manual.
The following two items should be considered during the design process.
1)
Diversion of storm water away from the natural watercourse will not be allowed, except
within the property boundaries controlled by the developer under the following conditions: a)
The storm water is returned to its natural flowing watercourse prior to leaving the developer's
property, b) For watersheds greater than twenty (20) acres, a timing analysis of the existing
and diverted hydrograph must be performed to confirm that the peak flow rate has not been
increased at the point that it reenters the watercourse, as a result of the diversion.
2)
All developments shall provide adequate drainage outfall at the lower end of the site into an
existing street, alley, drainage, easements or right-of-way, or to the centerline of an existing
natural drain. Where a proposed street, storm drain, or open channel does not discharge into a
natural low or into an existing adequate drainage easement, then facilities and drainage
easements of adequate width — to contain the design discharge — shall be constructed and
dedicated to the centerline of an existing natural low within the same watershed. However,
when the natural low lies within the developer's property, the developer will only be required
to plat an easement to the centerline of the natural low; provided that the easement is able to
accommodate the facilities that will be built in conjunction with future development of that
property.
2.7 FLOODPLAIN MANAGEMENT
Floodplain management has changed over the years due to the National Flood Insurance Act
of 1968. Changes from the program included USGS maps being used with the delineation of
floodplains, HUD issuing flood insurance maps in the late 1970’s, and the founding of FEMA
in 1979. The National Flood Insurance Program was ultimately placed under FEMA. As the
City began participating in this action in the late 1970’s, flood insurance can be purchased
through insurance carriers for buildings in Bexar County.
Floodplain management is used to minimize flooding of buildings, reduce flood losses, and
improve the quality of life — and safety of the citizens of Bexar County.
2.8 IMPLEMENTATION
The provisions of this manual shall apply to any application for subdivision plat, master
development plan, capital improvement project, or building permit approval except as
otherwise provided by Chapter 35 of the UDC. A storm water management plan shall be
provided as set forth in Appendix “A” of this manual.