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CHAPTER 1-B |
SECTION 11 DRAINAGE AND
FLOOD PROTECTION |
- BACKGROUND
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- Due to a semi-arid
climate and the topography of the Front Range, many of the drainage
channels in El Paso County are naturally dynamic and unstable.
As new development occurs, impervious surfaces replace a portion
of natural permeable surfaces. Impervious surfaces contribute
to increased and concentrated stormwater flows from rain and
snow melt and can have an adverse impact on stormwater quality.
A drainage system’s failure to adequately manage increased
stormwater flows may also result in serious property damage,
loss of life and impacts to area wildlife and the environment.
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- Responsibility
for construction and maintenance of drainage facilities in unincorporated
areas has traditionally been shared between individual property
owners and the Public Works Department. Historically, there has
not been a dedicated revenue source for funding public drainage
systems. More recently, a regional fee system has been developed,
using a basin planning approach. Out of a total of 139 identified
basins approximately 30 have now been studied in detail, with
fees developed; however, these calculated per-acre fees are only
collected at the platting stage, and do not include funding for
maintenance. Alternative funding methods, based on impervious
surface coefficients from roofs and paved areas, and/or drainage
utility fees, are being considered by a regional task force.
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- Flood plain management
in El Paso County is subject to federal mandates and is largely
a function of the Regional Building Department. Approximately
four percent (4%) of the entire County is designated as regulatory
100-year floodplains. Of the 8,000 improved properties located
within the floodplain
in El Paso County, 42% are situated in unincorporated areas.
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- ISSUE 11.1 encourage
Basin-wide Drainage Planning
- There is a tendency
among property owners, developers and public entities to design
solutions which move runoff water off site as fast as possible.
Because storm events are infrequent but often intense, public
interest in drainage planning issues surface only after storms
with significant impact, and therefore, support for drainage
studies and improvements is sporadic.
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- Although almost
all development activities adversely impact the amount, intensity
or quality of stormwater, these impacts are highly variable depending
on the type and intensity of development. Therefore, it is difficult
to effectively plan drainage improvements unless the ultimate
basin-wide land uses are known with reasonable certainty. Often
uncontrolled drainage impacts are compounded incrementally, resulting
in severe downstream problems and environmental degradation,
which in turn are not seen or experienced by upstream contributors.
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- Assuming that adequate
land and funding are available, a system which uses regional
stormwater detention facilities
reduces downstream problems and has the potential advantage of
management simplicity. One limitation to this approach is that
it does little to address upstream channel degradation. There
may also be difficulty in identifying and acquiring sites for
regional drainage facilities, especially in previously developed
areas.
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- Conversely, a system
of smaller on-site drainage facilities potentially can resolve
drainage or erosion problems at their source, thereby reducing
overall system degradation; however, locations may not be available
for on-site systems and maintenance safety issues can be complicated.
- While drainage
impacts tend to accrue incrementally as development takes place,
facilities often need to be constructed in major phases. Timing
problems may be further compounded depending upon where development
is occurring within a basin. New development increases runoff
flow for all downstream structures. Recently constructed downstream
drainage structures can quickly become obsolete unless designed
to accommodate projected upstream development.
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- Goal 11.1 Promote regional planning and management
approaches which protect the integrity of drainage systems and
minimize long-term system-wide environmental impacts, costs and
recognized flood dangers within the County.
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- Policy 11.1.1
- Determine basic
design and land requirements in each watershed for drainage facilities
at the earliest possible juncture in the planning process to
maximize planning options and minimize acquisition and construction
costs.
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- Policy 11.1.2
- Encourage an approach
based on the entire watershed, to flood protection which incorporates
a combination of on-site, sub-regional and regional retention
and detention facilities
to effectively reduce negative downstream impacts including erosion,
flooding, channel and
water quality degradation.
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- Policy 11.1.3
- Set aside the areas
needed to accommodate the drainage facilities necessary for full
basin build-out.
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- Policy 11.1.4
- Require development
plans to effectively address both quantitative and qualitative
impacts of drainage within the project site.
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- Policy 11.1.5
- Effectively utilize
automated land use mapping and data management (GIS)
to keep drainage basin planning studies current.
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- Policy 11.1.6
- Continue to support
cooperative multi-jurisdictional approaches to drainage system
planning and operations.
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- Policy 11.1.7
- Approve site-specific
development plans only if there are financial and other assurances
that on-site drainage facilities will be appropriately constructed,
that downstream infrastructure will accommodate the additional
impact, and maintenance issues are fully addressed.
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- Policy 11.1.8
- Promote planning
approaches which allow for interim solutions for drainage problems
in less developed basins.
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- Policy 11.1.9
- Support the development
of drainage basin management plans which meet the unique needs
of rural and rural-residential areas.
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- ISSUE 11.2 consider
Funding
- The combined costs
of on-site and regional drainage system design, land acquisition,
and construction significantly contribute to the cost of new
development.
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- The average cost
for a full drainage basin study is currently $75,000 and may
contribute to the difficulty in initiating a study at an early
point in the development of a basin.
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- The cost for regional
systems alone currently averages about $5,000 per developed acre.
Presently there is no dedicated funding source, such as a drainage
utility fee, to pay for correcting existing deficiencies or the
maintenance which is necessary once facilities are constructed.
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- Goal 11.2 Develop a more equitable
and inclusive system for funding the planning, construction and
maintenance of regional drainage facilities.
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- Policy 11.2.1
- Support the development
of drainage funding methods which most equitably allocate costs
according to the relative impacts caused by each property.
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- Policy 11.2.2
- Promote the development
of a dedicated funding source for the operation and maintenance
of existing and new regional drainage systems.
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- Policy 11.2.3
- Discourage the
inclusion of high-cost drainage improvements in drainage basin
planning studies (e.g. those which benefit a particular property)
unless a system-wide benefit can be demonstrated.
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- ISSUE 11.3 Maximize
Environmental Protection and Multiple Use Opportunities
- State law requires
new subdivisions to maintain regulatory runoff volumes during
100-year events. Many drainage systems are not adequately designed
to allow for enhanced runoff resulting from development.
Because the enhanced
runoff is generally more concentrated and accelerated, the potential
for negative impacts to the environment and downstream property
owners is significant.
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- Drainage facilities
can provide a variety of land use opportunities including open
space buffers, preservation of sensitive natural features such
as wetlands, ground water recharge zones, natural springs and
riparian ecosystems, and can serve as trail, wildlife and utility
corridors; however, these same opportunities may become constrained
due to safety concerns, lack of maintenance, and environmental
degradation. Traditionally drainage corridors have often been
viewed by developers and property owners as negative amenities
which should be fenced off and obstructed from view. Drainage-ways
which are not incorporated into development plans are more prone
to accumulations of litter, illegal filling and acts of vandalism.
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- Goal 11.3 Promote the planning and design of drainage
facilities which maximize on-site amenities while minimizing
detrimental downstream erosion.
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- Policy 11.3.1
- Where feasible,
support the use of natural or naturalistic drainage approaches
rather than hard line solutions.
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- Policy 11.3.2
- When possible,
safely design and incorporate drainage facilities as an aesthetic
element within developments.
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- Policy 11.3.3
- Fully evaluate
the relative impact of proposed drainage improvements on the
maintenance of water quality.
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- Policy 11.3.4
- Promote the effective
use of innovative short and long term strategies including sediment
ponds, buffer strips, and constructed wetlands as a means of
reducing peak flows and improving storm water quality.
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- Policy 11.3.5
- Protect the integrity
of wetlands, riparian areas and associated wildlife habitat through
a combination of careful land development and drainage system
design.
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- Policy 11.3.6
- Encourage the effective
use of control measures to mitigate the short and long term erosion
impacts of development.
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- ISSUE 11.4 Reduce Flood
Danger
- Reasonable alternatives
for addressing existing structures which are located in the flood
plain are limited; however there are a number of engineering,
regulatory and warning systems approaches which can partially
mitigate this danger and potential for financial loss.
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- Planning for flood
protection while reducing flood danger is a challenge because
flood-prone areas are extensive and actual floodplain
boundaries are subject to change due to channel migration caused
by erosion. Rates of bank erosion may be accelerated as a result
of upstream development activities and result in changes to the
FEMA the Regulatory
100-year Flood Plain designation.
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- Additional development
within floodplain areas
increases risk of loss and impedes the ability of drainage channels
to convey stormwater. However, the strictest interpretation of
floodplain regulations
may severely limit the use of private property.
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- Goal 11.4 Promote public safety and
reduce loss of private property.
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- Policy 11.4.1
- Strongly discourage
land use development from locating in designated floodplains.
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- Policy 11.4.2
- Strongly discourage
land use development from locating in areas below dams, spillways,
and levees that would require the State Engineer to upgrade the
classification of these structures.
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- Policy 11.4.3
- Encourage the removal
of existing structures within the flood-plain when this can be
accomplished in a cost-effective and equitable manner.
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- Policy 11.4.4
- Support the construction
of facilities which will protect existing structures in flood-prone
areas if this can be accomplished in a manner which is environmentally
sensitive and will not significantly reduce the ability of the
floodway to carry peak
flows.
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- Policy 11.4.5
- Support the continued
refinement and use of regional flood warning systems.
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- Policy 11.4.6
- Continue to encourage
the disclosure of flood hazards to current and future property
owners.
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- Policy 11.4.7
- Limit new development
in and modification of flood plains in accordance with regionally
adopted flood-plain regulations.
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- Policy 11.4.8
- Encourage "prudent
line" approaches which adequately set structures back
from flood-plain boundaries, especially in areas which may be
prone to bank erosion.
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- Note: Drainage policies and requirements
are set forth in Drainage Criteria Manual the City
of Colorado Springs and El Paso County. This document currently
advocates the use of large regional detention
basins rather than smaller facilities.
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