This manual and design standards with all future amendments
and revisions shall be known as the Stormwater Management Manual (herein
referred to as the manual or SWMM).
(Res. 40-08 (§ 201), 3-19-08)
This manual and design standards shall apply to all new development
and redevelopment within the boundaries of Mesa County, including
any public lands, facilities constructed on rights-of-way, easements
dedicated for public use, and to all privately owned and maintained
drainage facilities, including but not limited to detention ponds,
storm drains, inlets, manholes, culverts, swales, channels and water
quality facilities.
(a) Mesa County.
Chapter 7.7 of the Mesa County Land Development
Code (Code) requires that “Drainage facilities shall be designed
and installed in accordance with the Mesa County Stormwater Management
Manual.”
(b) City of Grand Junction.
The City of Grand Junction Zoning
and Development Code (GJMC Title 21) requires that “All proposed
development must provide for on-site runoff collection and conveyance
in accordance with the Stormwater Management Manual (SWMM) and applicable
federal and State laws.”
The City of Grand Junction adopted stormwater pollution prevention Ordinance Number 3824 (Chapter
13.28 GJMC), which requires that: “All proposed development … must provide for on-site erosion and sediment control, control of illegal discharges, and runoff collection and conveyance in accordance with the Stormwater Management Manual and applicable federal and State laws.”
(c) Other Jurisdictions.
The City of Fruita, the Town of
Palisade, and the Grand Junction Drainage District may adopt the Stormwater
Management Manual in whole or in part.
(Res. 40-08 (§ 202), 3-19-08)
(a) Municipality.
Powers to regulate land use activities,
including drainage, are granted to a municipality under Colorado Revised
Statutes as noted below:
§
31-15-701, C.R.S. et seq. grants municipalities the power to establish, improve,
and regulate such improvements as streets and sidewalks, water and
water works, sewers and sewer systems, and water pollution controls.
In addition, a municipality may, among other powers, deepen, widen,
pipe, cover, wall, alter or change the channel or watercourses.
§
31-25-501, C.R.S. et seq. authorizes municipalities to construct local improvements
and assess the cost of the improvements wholly or in part upon property
specially benefited by such improvements. By ordinance, a municipality
may order construction of district sewers for storm drainage in districts
called storm sewer districts. (For the City of Grand Junction, see
People’s Ordinance No. 33.)
§
31-25-601, C.R.S. et seq. authorizes municipalities to establish improvement
districts as taxing units for the purpose of constructing or installing
public improvements.
§
31-35-401, C.R.S. et seq. authorizes municipalities to operate, maintain,
and finance water and sewage facilities for the benefit of users within
and without their territorial boundaries. Sewerage facilities are
defined as “any one or more of the various devices used in the
collection, treatment or disposition of sewerage or industrial wastes
of a liquid nature or storm, flood or surface drainage waters….”
(b) County.
Powers to regulate land use activities, including
drainage, are granted to a county under Colorado Revised Statutes
as noted below:
§
24-67-101, C.R.S. et seq. (Planned Unit Development Act of 1972) power to
encourage more efficient and innovative use of the land for public
services and encourages integrated planning.
§
29-20-101, C.R.S. et seq. (Local Government Land Use Control Enabling Act
of 1974) clarifies and provides broad authority to local governments
to plan for and regulate the use of land within hazardous and environmentally
sensitive areas.
§
30-20-401, C.R.S. et seq. authorizes construction, maintenance, improvements
and financing of water and sewerage facilities for the County’s
own use and for the use of the public and private consumers and users
within and without the County’s territorial limit.
§
30-20-501, C.R.S. et seq. (County Public Improvement District Act of 1968)
authorizes creation of public improvement districts within any county
as taxing units and for the purpose of implementing public improvements.
§
30-20-601, C.R.S. et seq. authorizes a county by resolution to construct local
improvements and to assess the costs to properties especially benefited
by improvements.
§
30-28-101, C.R.S. et seq. provides the County with planning authority, such
as development of master plans and adoption of such plans by resolution;
creation of a regional planning commission; and regulation of development
density.
§
30-30-101, C.R.S. et seq. (control of stream flow) provides power to remove
any obstruction to the channel of any natural stream which causes
a flood hazard and provides a right of access to any such natural
stream.
§§
37-20-101 and
37-33-101, C.R.S. et seq. authorizes the owner of agricultural lands susceptible
to drainage problems from the same general system to petition the
Board of County Commissioners to set up a drainage district.
(Res. 40-08 (§ 203), 3-19-08)
(a) Mesa County.
The Director or an authorized representative
is responsible for enforcing the provisions of this manual.
(b) City of Grand Junction.
The City Manager or the City
Manager’s designee is responsible for enforcing the provisions
of this manual.
(c) Other Jurisdictions.
Contact the City of Fruita, the
Town of Palisade, or the Grand Junction Drainage District for information.
(Res. 40-08 (§ 204), 3-19-08)
All drainage submittals will be reviewed for general compliance
with this manual. An acceptance does not relieve the owner, engineer,
or designer from responsibility of ensuring that the calculations,
plans, specifications, construction, and record drawings comply with
this manual.
Adequate time must be allocated in development planning to permit
a complete review. The intent of this manual is to more clearly define
the requirements and reduce the time and effort required to develop
an acceptable drainage design.
(a) Mesa County.
Acceptance of final drainage report and
drainage facility construction plans shall be valid for two years.
Documents with approvals more than two years old may require revision
prior to development to comply with the provisions of the manual in
effect at that time. Amendments to this manual will apply to all drainage
reports submitted after the effective date of the amendment. Final
drainage reports are exempt from an amendment provided they are submitted
for approval within 60 days after the effective date of an amendment.
(b) City of Grand Junction.
Drainage submittals shall contain
all information required by this manual but the review process will
be in accordance with the City’s Submittal Standards for Improvements
and Development (SSID) and the Zoning and Development Code (GJMC Title
21).
(c) Other Jurisdictions.
Contact the City of Fruita, the
Town of Palisade, or the Grand Junction Drainage District for information.
(Res. 40-08 (§ 205), 3-19-08)
In the interpretation and application of the provisions of the
manual, the following shall govern:
(a) Minimum Standards.
This manual shall be regarded as
the minimum requirements for analysis and design of storm drainage
facilities. Special site conditions or mitigation for potential impacts
from new development or redevelopment may result in more stringent
standards.
(b) Higher Standards.
For Mesa County if provisions of the
code, any law, ordinance, resolution, rule, or regulation contains
restrictions covering the same subject matter, the more stringent
standards or requirements shall govern. For the City of Grand Junction
if provisions of the Zoning and Development Code (GJMC Title 21),
any law, ordinance, resolution, rule, or regulation contains restrictions
covering the same subject matter, the more stringent standards or
requirements shall govern.
(c) Flexibility.
There may on occasion be need for site-specific
application and interpretation of this manual. The Director in Mesa
County or the City Manager or the City Manager’s designee in
the City of Grand Junction may deviate from the requirements of this
manual; provided, that the approved plan is compatible with surrounding
in-place improvements and is sufficiently protective. The burden of
responsibility shall be on the applicant to show that the requested
deviation/variance from standards does not create a public hazard.
(d) Abrogation.
This manual shall not abrogate or annul
any permits or approved drainage reports, construction plans, easements,
or covenants issued before the effective date of this manual.
(Res. 40-08 (§ 206), 3-19-08)
(a) Deviations/variances from specific standards, procedures, or criteria
in this manual may only be requested for:
(1) Unusual situations where strict compliance with the manual may not
protect the public health and safety; or
(2) Unusual situations which require additional analysis outside the
scope of the manual for which the additional analysis shows that strict
compliance with the manual may not protect the public health and safety;
or
(3) Unusual hydrologic and/or hydraulic conditions which cannot be adequately
addressed by strict compliance with the manual.
(b) Mesa County.
A variance from the technical provision of this manual may be granted by the Director. All requests for variances shall be submitted in writing (normally with the drainage report, see Chapter
28.12 GJMC), shall state the provision for which the variance is requested, and shall provide evidence, data or other information in support of the request. The Director will review and rule on the request and provide his findings in writing.
(c) City of Grand Junction.
A deviation from any requirement
of this manual may be granted by the City Manager or the City Manager’s
designee. A request for deviation shall be submitted in writing as
a separate letter attached to the drainage report. The request shall
state the provision for which the deviation is requested and shall
provide supporting evidence, data, or other appropriate information.
The City Manager or the City Manager’s designee shall review
and rule on the request and provide the findings in writing.
(d) Other Jurisdictions.
Contact the City of Fruita, the
Town of Palisade, or the Grand Junction Drainage District for information.
(Res. 40-08 (§ 207), 3-19-08)
The following acronyms are used within the context of this manual:
BMP
|
Best Management Practice
|
CAP
|
Corrugated Aluminum Pipe
|
CAPA
|
Corrugated Aluminum Pipe Arch
|
CMP
|
Corrugated Metal Pipe
|
CMPA
|
Corrugated Metal Pipe Arch
|
CDOT
|
Colorado Department of Transportation
|
CDPHE
|
Colorado Department of Public Health and Environment
|
CDPS
|
Colorado Discharge Permit System
|
CRS
|
Colorado Revised Statutes
|
CSP
|
Corrugated Steel Pipe
|
CSPA
|
Corrugated Steel Pipe Arch
|
CSWMP
|
Construction Stormwater Management Plan
|
CWA
|
Clean Water Act
|
CWCB
|
Colorado Water Conservation Board
|
EC
|
Erosion Control
|
ECP
|
Erosion Control Plan
|
EGL
|
Energy Grade Line
|
EPA
|
Environmental Protection Agency
|
FEMA
|
Federal Emergency Management Agency
|
GIS
|
Geographic Information System
|
HDS
|
Hydraulic Design Series
|
HEC
|
Hydrologic Engineering Center or Hydraulic Engineering Circular
(FHWA)
|
HERCP
|
Horizontal Elliptical Reinforced Concrete Pipe
|
HGL
|
Hydraulic Grade Line
|
MS4
|
Municipal Separate Storm Sewer System
|
NAVD
|
North American Vertical Datum
|
NFIP
|
National Flood Insurance Program
|
NOAA
|
National Oceanic and Atmospheric Administration
|
NRCS
|
Natural Resource Conservation Services, formerly the SCS
|
NPDES
|
National Pollutant Discharge Elimination System
|
NWS
|
National Weather Service
|
PE
|
Professional Engineer licensed by the State of Colorado
|
PMF
|
Probable Maximum Flood
|
PVC
|
Polyvinyl Chloride
|
RCBC
|
Reinforced Concrete Box Culvert
|
RCP
|
Reinforced Concrete Pipe
|
ROW
|
Right-of-Way
|
SCS
|
Soil Conservation Service
|
SPP
|
Structural Plate Pipe
|
SSID
|
Submittal Standards for Improvements and Development (City of
Grand Junction)
|
SWMM
|
Stormwater Management Manual
|
SWMP
|
Stormwater Management Plan (either the construction SWMP or
the final drainage report containing post-construction BMPs)
|
TAC
|
Technical Advisory Committee
|
TRC
|
Technical Review Committee
|
UDFCD
|
Urban Drainage and Flood Control District (Denver, Colorado)
|
USACE
|
United States Army Corps of Engineers
|
USBR
|
United States Bureau of Reclamation
|
USDCM
|
Urban Storm Drainage Criteria Manual, prepared by the Urban
Drainage and Flood Control District in three volumes
|
USGS
|
United States Geological Survey
|
WQCD
|
Water Quality Control Division of the Colorado Department of
Public Health and Environment
|
WQCV
|
Water Quality Capture Volume
|
(Res. 40-08 (§ 208), 3-19-08)
Applicant
means a qualified agent, individual or firm acting on behalf
of the owner of property requesting approval of plans for new development
and redevelopment.
Authority or Drainage Authority.
Mesa County, the Cities of Grand Junction and Fruita, the
Town of Palisade, and the Grand Junction Drainage District have contracted
through intergovernmental agreements (IGA) to form the 5-2-1 Drainage
Authority (Authority), under Colorado Revised Statutes, specifically
§
29-1-204.2, C.R.S.
Best management practices
means schedules of activities, prohibitions of practices,
maintenance procedures, and other management practices to prevent
or reduce the pollution of State waters. BMPs also include treatment
requirements, operating procedures and practices to control site runoff,
spillage or leaks, sludge or waste disposal, or drainage from raw
material storage.
CDPS permit
means a permit issued by the State of Colorado under Part
5 of the Colorado Water Quality Control Act that authorizes the discharge
of pollutants to waters of the State, whether the permit is applicable
to a person, group or area.
Channel
means a natural or artificial low-lying area with a definite bed and banks, which confines and conveys continuous or periodic flows of water. (Mesa County Land Development Code Section 12.1 and GJMC §
21.10.020, Terms defined.)
Commercial
means any business, trade, industry or other activity engaged
in profit.
Construction activity
includes clearing, grubbing, filling, grading, and excavation.
Does not include routine maintenance performed by public agencies,
private parties, or their agents to maintain original line and grade,
hydraulic capacity, or original purpose of the facility. Also see Land disturbance. [(Adapted from CDPS General Permit No.
COR-030000 @ Part I A(2)(a)]
Construction site
means any location where construction or construction related
activity occurs.
Construction stormwater management plan
means a specific individual construction plan that describes
the BMPs to be implemented at a site to prevent or reduce the discharge
of pollutants during construction activities.
Director
means the Mesa County Planning Director or designee when
referring to a Mesa County official, but the City Manager or his designee
when referring to a City of Grand Junction official.
Discharge
means the addition or release of any pollutant, stormwater,
subsurface, groundwater or any substance whatsoever to the storm drainage
system.
Downstream
refers to locations which are hydraulically lower in elevation
than the location at which the comparison is being made. Downstream may include locations outside of the stream, channel, pipe, etc.,
such as sheet flow, which often meanders in several directions.
Drainageway
means any natural or artificial (manmade) channel which provides
a course for water flowing either continuously or intermittently to
downstream areas.
Final stabilization
means when all soil disturbing activities at the site have
been completed, and uniform vegetative cover has been established
with a density of at least 70 percent of pre-disturbance levels, or
equivalent permanent, physical erosion reduction methods have been
employed. For purposes of the construction SWMP, establishment of
a vegetative cover capable of providing erosion control equivalent
to pre-existing conditions at the site will be considered final stabilization.
Flood
means a temporary rise in a watercourse, flow, or stage, that results in water overtopping its banks and inundating areas adjacent to the channel. (Mesa County Land Development Code Section 12.1; see also GJMC §
21.10.020, Terms defined.)
Grand Valley
means the portion of Mesa County whose boundary is approximated
by the 5,000-foot elevation contour and extends west of the community
of Mack, along the north eastern edge of the Colorado National Monument,
south of Whitewater, to the east of Palisade, and along the face of
the Bookcliffs to the north.
Land disturbance
means a manmade change in the existing cover or topography
of the land, including grading, excavation, filling, building, paving,
and other activities that may result in or contribute to soil erosion
or sedimentation in the discharge of pollutants.
Local facility
means a detention and/or water quality facility that has
been sized based on the area and imperviousness of the watershed that
includes all the development that drains to the facility, but is not
publicly owned and maintained. Also see Regional facility and On-site facility.
Local jurisdiction,
within the context of the SWMM, means Mesa County, City of
Grand Junction or Fruita, Town of Palisade, or the Grand Junction
Drainage Authority.
Major drainage system
means a stormwater facility, such as a channel, large conduit,
detention or retention, which receives storm runoff from a watershed
generally 160 acres in size or larger.
Municipal separate storm sewer system (MS4)
means a conveyance or the system of conveyances, including
roads with drainage systems, municipal streets, curbs, gutters, ditches,
drainage inlets, catch basins, pipes, tunnels, culverts, channels,
detention basins and ponds owned and operated by a municipality or
county and designed or used for collecting or conveying stormwater
that is not a combined sewer or used for collecting or conveying sanitary
sewage.
New development and redevelopment.
For Mesa County definition, refer to the Mesa County Land
Development Code. For the City of Grand Junction definition, refer
to GJMC Title 21, Zoning and Development. For the City of Fruita,
Town of Palisade and the Grand Junction Drainage District definitions,
refer to the applicable development codes.
NPDES
means the National Pollutant Discharge Elimination System
under Section 402 of the Clean Water Act.
On-site facility
means a local facility that is contained within and only
serves the development in question and not other developments.
Outfall drainage system
means the drainage system typically consisting of swales,
curb and gutter, storm drains, and sometimes small open channels that
discharge to a major drainage system. Also called “local drainage
system.”
Owner
means a person having dominant and/or servient interest in
property, having sufficient interest to convey property, and/or having
possessory interest in property. The term owner also
includes the owner’s agent.
Part of a larger common plan of development or sale
means a contiguous area where multiple separate and distinct
construction activities will take place at different times on different
schedules under one plan. An example would be a commercial development
with multiple separate buildings constructed over the course of multiple
construction schedules.
Pollutant
means dredged spoil, dirt, slurry, solid waste, incinerator
residue, sewage, sewage sludge, garbage, trash, chemical waste, biological
nutrient, biological material, radioactive material, heat, wrecked
or discarded equipment, rock, sand, or any industrial, municipal,
or agricultural waste. [§
25-8-103(15), C.R.S.]
Pollution
means the alteration of the physical, thermal, chemical,
or biological quality of, or the contamination of any water that renders
the water harmful, detrimental, or injurious to humans, animal life,
plant life, property or public health, safety or welfare, or impairs
the usefulness or the public enjoyment of the water for any lawful
or reasonable purpose.
Post-construction stormwater management plan
means the final drainage report, in accordance with GJMC §
28.12.060 through
28.12.110, final drainage report, which includes a combination of structural and/or nonstructural BMPs, further described in Chapter
28.64 GJMC, Post-Construction Stormwater Management, that reduce the discharge of pollutants after construction is complete.
Private drainage system
means all privately owned ground, surfaces, structures or
systems, excluding the MS4, that contribute to or convey stormwater
including but not limited to roofs, gutters, downspouts, lawns, driveways,
pavement, roads, streets, curbs, gutters, inlets, drains, catch basins,
pipes, tunnels, culverts, channels, detention basins, ponds, draws,
swales, streams and any ground surfaces.
Public improvement
means any improvement, facility or service together with
its associated public site, right-of-way or easement necessary to
provide transportation, drainage, public private utilities, parks
or recreational, energy or similar essential services. (Mesa County
Land Development Code Section 12.1.)
Recurrence Interval.
The recurrence interval corresponds to the statistical return
period of an event of the same intensity (e.g., a 100-year recurrence
interval flood has a one percent chance to occur each year, which
does not mean that it will occur every 100 years).
Regional facility
means a detention and/or water quality facility that is publicly
owned and maintained and serves all properties within the tributary
watershed.
Sediment
means soil, mud, dirt, gravel and rocks that have been disturbed,
eroded and/or transported naturally by water, wind or gravity and/or
mechanically by any person, vehicle or equipment.
Significant materials
include but are not limited to: raw materials; fuels; materials
such as metallic products; hazardous substances designated under Section
101(14) of CERCLA; any chemical the facility is required to report
pursuant to Section 313 of Title III of SARA; fertilizers; pesticides;
and waste products such as ashes, slag and sludge that have the potential
to be released with stormwater discharge.
Storm drainage system
means all surfaces, structures and systems that contribute
to or convey stormwater including private drainage systems and the
MS4, and any nonmunicipal drain or pipe, channel or other conveyance,
including natural and artificial (manmade) washes and ditches for
conveying water, groundwater, drainage water or unpolluted water from
any source, excluding sewage and industrial wastes, to waters of the
State and United States.
Storm water or stormwater.
Within the context of the Stormwater Management Manual, stormwater,
whether one or two words, shall mean surface runoff resulting from
precipitation.
Stormwater construction permit
means the permit issued by the CDPHE called the general permit
for stormwater discharges associated with construction activities.
Mesa County or the City of Grand Junction will also issue a stormwater
construction permit for land disturbances related to new development.
Stormwater management plan.
Within the context of the Stormwater Management Manual, a
stormwater management plan (SWMP) means the construction SWMP (CSWMP)
and/or the post-construction SWMP.
Stream channel
means the area of the floodplain which carries the normal
flow of the watercourse. (Mesa County Land Development Code Section
12.1).
Urbanized area
means the area identified by the Colorado Department of Public
Health and Environment based on the 2000 census and called the urban
area of Mesa County. Within the context of the SWMM, urban area also
includes the Redlands within the urban growth boundary of the County.
Water quality capture volume
means the minimum storage volume, based on the eightieth
percentile event, which is retained and released over a specified
period of time, depending on the specific structural BMP and is based
on the time it takes to fully drain the brim-full volume contained
in storage.
Water quality outlet
means a structure designed to release the water quality capture
volume over the specified period of time for the specific BMP.
Waters of the State
means any groundwater, percolating or otherwise, lakes, bays,
ponds, impounding reservoirs, springs, rivers, streams, creeks, estuaries,
marshes, inlets, canals, wells, watercourses, drainage systems, and
irrigation systems; all sources of water such as snow, ice, and glaciers;
and all other bodies or accumulations of water, surface and underground,
natural or artificial, navigable or nonnavigable, and including beds
and banks of all watercourses and bodies of surface water, public
or private, located wholly or partly within or bordering upon this
State and within the jurisdiction of this State.
Watershed master plan
means the Grand Valley Stormwater Management Master Plan
or other stormwater master plans approved by the Drainage Authority
representing applicable municipalities and Mesa County.
Wetland
means any area that is inundated or saturated by surface
or groundwater at a frequency and duration sufficient to support,
under normal circumstances, a prevalence of vegetation typically adapted
to the saturated soil conditions. Wetlands generally include swamps,
marshes, bogs and similar areas.
(Res. 40-08 (§ 209), 3-19-08)