Final Baseline Hydrology Report - October 2012 - Urban Drainage ...

Sanderson Gulch Major Drainageway Plan
Baseline Hydrology Report October 2012
Landscape and Ecology. Sanctuary Park and Robbins-Dasher Lake are at the headwaters of North
Sanderson Gulch. This is a native wildlife habitat park which is dominated by riparian species of
cottonwoods, willows, cattails and phragmites. Invasive species thistle, kochia, smartweed, bindweed,
prickly lettuce, common mallow, barnyard grass, Johnsongrass, pigweed, rag weed, curly dock, alfalfa,
Chinese elm, Siberian elm and Russian olive.
Maintenance. Routine maintenance responsibilities of the pipe and city-owned park are performed by the
City of Lakewood.
Parks and Recreation. Public bicycle and pedestrian access along the piped segment is provided on-street
and by attached sidewalks along W. Florida Avenue. Green Gables Park (11.82 acres) and Sanctuary Park
(10.69 acres) are bisected by S. Garrison Street. Green Gables Park includes 0.63 acres of water surface
in its pond, and also includes softball and soccer athletic fields, paved parking, playground and restroom
facilities. Sanctuary Park includes a 3.09 acre pond and natural areas, and has a gravel trail with wildlife
observation overlooks.
Sanderson Gulch watershed at Jewell Park Pond. During a major storm, the open channel could fill with
stormwater and be a potential import to Sanderson Gulch. However, with an emergency overflow located at
Mississippi Avenue, the Weir Gulch watershed tributary basin to the Agricultural Ditch downstream of the
spill is relatively minor and considered insignificant.
2.4.2 Ward Canal
The Ward Canal, operated by the Ward Canal Company, supplies water to Kendrick Lake No. 1, Kendrick
Lake, Smith Reservoir, Ward Reservoir No. 1 and Ward Reservoir No. 2 within the Sanderson Gulch
watershed. The canal is open channel in some areas, but mostly piped underground through a majority of
the reach in Sanderson Gulch. Because the canal is located along the ridgeline of the basin divide between
Bear Creek and Sanderson Gulch, there is little area tributary to the canal. The amount of stormwater that
could be imported or exported by the Ward Canal during a significant storm event is insignificant to the
Sanderson Gulch major storm hydrology.
Water Quality. Water quality treatment occurs within Sanctuary Park which acts as a 100-year retention
pond. Passive water quality occurs within Robbins-Dasher Lake in Green Gables Park.
2.4 Irrigation Ditches
Irrigation ditches are an important consideration for Major Drainageway Planning studies. In the past, it has
been common practice to ignore irrigation ditches, assuming they are full and runoff simply flows across
them. However, during a major storm event, these open channel ditches can import or export flow from a
drainage basin which should be considered in the hydrologic model. Piped irrigation ditches are less of a
concern regarding stormwater runoff interaction. Additionally, municipalities are attempting to disconnect
urban storm drainage from the irrigation ditches for liability and water quality concerns.
The Sanderson Gulch headwaters receive irrigation water from two major ditches as shown on Figure 2-4:
• Agricultural Ditch which diverts water from Clear Creek
• Ward Canal which diverts water from Bear Creek
2.4.1 Agricultural Ditch
The Agricultural Ditch is operated by the Agricultural Ditch & Reservoir Company and also operates Smith
Reservoir within the Sanderson Gulch drainage basin, and Main and East Reservoirs within the Weir Gulch
drainage basin. The Agricultural Ditch is generally an open channel ditch which could have an interaction
with surface stormwater runoff. It has emergency overflow spill points at Mississippi Avenue to discharge
into Weir Gulch if necessary, and at Jewell Park Pond to discharge into Sanderson Gulch if necessary.
Smith Reservoir has a 250 acre tributary basin, included the reservoir itself. Smith Reservoir is able to
contain a 100-year storm event. However, during normal operations and in an emergency situation, Smith
Reservoir can send water into East Reservoir. If East Reservoir were to spill, water would be intercepted by
the Agricultural Ditch and conveyed into Sanderson Gulch to Jewell Park Pond to the emergency spill point.
For the purposes of this study, the Agricultural Ditch is not expected to have an impact on major storm
hydrology. If Smith Reservoir were to spill (potential export), this water would be returned back to the
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