BOARD00391

• Board Meeting Date: 5/23/2005
• Description: Flood Section - Floodplain Rules and Regulations Opportunity for Board and Public Comment
• Board Meetings - Doc Type: Memo

Rule 11. Effects of Flood Mitigation Measures and Stream Alteration Activities on Regulatorv
. Floodplains
In order to assist the CWCB in carrying out its mission to protect the health, safety, arid
welfare of the public, through the prevention of floods in Colorado, the CWCB requires the
following:
A. Detention/flood control storage shall be designed and constructed as part of a basinwide
program for the watershed.
B. Detention facilities shall adequately consider flow rates and flow volumes.
C. Flood control channels shall include a low-flow channel with a capacity to convey the
average annual flow rate, or other appropriate flow rate as determined through a
hydro geomorphological analysis, without excessive erosion or channel migration, with
an adjacent overbank floodplain to convey the remainder of the lOO-year flow. The
channel improvement shall not cause increased velocities or erosive forces upstream
and downstream of the improvement.
D, Channelization and flow diversion projects shall appropriately consider issues of
sediment transport, erosion, deposition, and channel migration and properly mitigate
potential problems through the project as well as upstream and downstream of any
improvement activity. A detailed geomorphological analysis shall be performed to
assist in determining the most appropriate design.
E. Low-lying areas (below BFE) "protected" by levees, flood fringe areas raised by fill, or
perched flow diversion or channelization proj ects shall not be considered to be removed
from the 100-year floodplain for the purpose of building basements.
F. Project proponents for a mitigation activity must evaluate the residual 1 OO-year
floodplain. Proponents are also encouraged to map the 500-year residual floodplain
. floodplain for the evaluation of critical facilities.
G. All flood protection and mitigation projects shall be maintained to ensure that they
maintain their structural and hydraulic integrity. Annual inspections including, as
appropriate, field surveys of stream cross-sections, shall demonstrate to the appropriate
regulatory jurisdictions that the project features are in satisfactory structural condition,
the adequate flow capacity remains available for conveying flood flows, that no
encroachment by vegetation, animals, geological processes such as erosion, deposition,
or migration, or by human activity, endarlger the proper function of the proj ect. If any
significant problems are noted in such annual inspections, the local regulatory
jurisdiction shall notifY the CWCB within 30 days of said problems.
H. Any stream alteration activity proposed by a project proponent must be evaluated for its
__ _~ ~_____irnpact on the regulatorY floodplain and b~jn c~E1pliance withfede!.ah~t<lte and local
floodplain rules, regulations and ordinances. ~ -- -- --
1. Any stream alteration activity shall be designed and sealed by a registered professional
engmeer.
J. Stream alteration activities shall be properly permitted by local, state and federal
agencies and shall be in conformance with FEMA floodplain regulations (44 C.P.R.).
K. Stream alteration activities shall not be constructed unless the project proponent
demonstrates through a floodway analysis arid report, sealed by a registered
professional engineer, that there are no adverse floodway and floodplain impacts
resulting from the project.
L. No adverse floodway impact is defined as a O.O-foot rise in the proposed conditions
. versus existing conditions floodway. Proposed increases to the regulatory 1 DO-year

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