Drainage Overview - Maricopa County Department of Transportation

Normal depth (Modified Puls) channel routing methodology was used to route runoff
through subbasins. An eight-point composite channel cross-section was estimated from 10ft
topography, aerial photography, and field observations to represent typical wash crosssection
conveyance. Reservoir routing was performed upstream of the CAP canal using
stage-storage data from the Wagner Wash Floodplain Delineation Study Hydrology Report.
Flow diversions were estimated as simple percentages for the entire range of discharges
using the 10-ft topography, aerial photography, and field observations. Retention from the
100-year, 2-hour storm event was diverted out of the future land use conditions models.
4.1.2 Wittmann Watershed
This watershed was divided into eight major sub-watersheds, four of which encompass the
Deer Valley Parkway study area: the Sun Valley Parkway, Iona Wash, Trilby Wash, and
Wittmann Wash sub-watersheds. The 100-year, 6-hour and 24-hour storm events for both
the existing and ultimate development land use conditions were modeled using HEC-1
software. Methods and procedures were based on the FCDMC Hydrology Manual.
Watershed Modeling System (WMS) software was used to prepare the input parameters for
the HEC-1 models.
NOAA Atlas 2 rainfall data was used to estimate the design rainfall depth for this study.
Depth-area reduction factors were applied with the use of JD records. FCDMC 6-hour local
storm distributions for the 6-hour model and the SCS Type II precipitation distribution for
the 24-hour model were used for HEC-1 rainfall distributions. The Green and Ampt Method
was utilized for the estimation of rainfall losses. The Clark Unit Hydrograph was used for
the development of unit hydrographs.
Normal depth channel routing methodology was utilized in the hydrologic model to route
surface runoff through subbasins. An eight-point composite channel cross-section was
developed to represent typical wash cross-section conveyance. The longitudinal slopes and
Manning’s “n” values were estimated based on topographic mapping, aerial photographs,
and field reconnaissance estimates. Storage routing behind the CAP canal was modeled
using level pool routing. Stage/discharge relationships for the over-chutes were developed
assuming critical flow through the structure. Normal depth calculations were used to
calculate most of the flow splits, although two-dimensional analyses were conducted for
four complex split flow locations. Three of those split flow locations are in the Iona Wash
sub-watershed upstream of the CAP canal. The fourth split flow is located north of the
CAP canal and east of US 60. All four of the split flows modeled with two-dimensional
analysis are located upstream of the study area. As mentioned in Section 3.4.1, there are
additional areas within the Wittmann watershed that may require two-dimensional modeling
due to the lack of identifiable drainage patterns.
4.1.3 McMicken Dam Watershed
Hydrologic modeling of the watershed contributing to McMicken Dam was conducted to
assess flows entering the dam at key inflow locations. Therefore, although the watershed is
very similar to the Wittmann Watershed, the subbasins are much larger. WMS software
was used to calculate runoff for the 100-, 200-, and 500-year, 24-hour storm events for both
existing and future land use conditions. The 6-hour and 72-hour Probably Maximum Flood
091337137, 2011-018, TT005 Maricopa County Department of Transportation
Technical Memorandum 3 Deer Valley Parkway Feasibility Study
Drainage Overview 22 April 2012