The 2010 Comprehensive Plan discusses Natural Hazards, which
include drainage and stormwater management. Drainage for Orchard Mesa
is managed by the City of Grand Junction, Mesa County, the Orchard
Mesa Irrigation District, and the 5-2-1 Drainage Authority. Although
the average annual precipitation for the Grand Junction vicinity is
only about nine inches, flooding can and does occur. Because large
storms are infrequent, drainage issues were overlooked in the past.
Our native clay soils do not absorb water well. Vegetation is sparse
in many areas and this encourages erosion. Finally, development increases
the amount of impervious surfaces in the form of roofs, driveways,
and parking lots, reducing the amount of open ground. These past practices
and environmental conditions collectively promote little infiltration,
rapid runoff, more debris in the runoff, and flash flooding.
In addition to flooding concerns, water quality is also important.
There are many entities that are involved in stormwater quality in
the Grand Valley, including Mesa County, City of Grand Junction, Town
of Palisade, Grand Valley Drainage District, Orchard Mesa Irrigation
District, Grand Valley Water Users’ Association, and School
District No. 51. The Grand Valley Stormwater Unification Feasibility
Study was conducted in 2003 and the 5-2-1 Drainage Authority was created
to help monitor and manage the quality of water as it returns to local
washes, creeks and rivers.
(Ord. 4629, 5-7-14)
To aid in returning runoff to water sources safely, the U.S.
Environmental Protection Agency (EPA) has developed a National Pollutant
Discharge Elimination System (NPDES) stormwater permitting program.
As part of the NPDES guidelines, employees in the Orchard Mesa Irrigation
District (OMID) and the Grand Valley Water Users Association have
the authority to monitor and report violations to the City of Grand
Junction or Mesa County. (http://www.irrigationprovidersgv.org/stormwater_discharge.php)
Generally, urban runoff will be treated as a pollutant, while agricultural
drainage is exempt from NPDES regulation. Increased stormwater drainage
in OMID’s system may add to the district’s permitting
and treatment requirements.
(Ord. 4629, 5-7-14)
The 5-2-1 Drainage Authority received a pre-disaster mitigation
grant from the Federal Emergency Management Agency (FEMA) in 2009
to address several known problems on Orchard Mesa. A comprehensive
drainage study, from 30 Road to the west, was completed as part of
the grant project, resulting in the following map (Figure 9; Appendix
Map 22). It identifies the area that would be inundated by a one percent
chance (100-year) event, which is two inches of rainfall in a 24-hour
timeframe. There are approximately 400 acres and 700 structures in
the floodplain. The study found that spending over $4,000,000 (2009
dollars) to perform improvements would remove approximately 100 acres
from the floodplain.
Figure 9: Orchard Mesa Flood Inundation Study
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Although FEMA has not created a Flood Insurance Rate Map (FIRM)
from this study, the City is using it as the “best available
information” to govern development in the area and to ensure
all new structures are built high enough they will not flood in the
one percent chance event. Because this is not yet a FIRM, lending
agencies probably won’t require flood insurance to issue a loan.
Affected landowners should consider obtaining flood insurance because
basic homeowner’s policies do not cover flooding. A composite
of the study area plus the FEMA-regulatory floodplain is shown in
Appendix Map 23.
(Ord. 4629, 5-7-14)