HomeMy WebLinkAboutTR 35337 HYDROLOGY REPORT-030 Spyglass Ranch Tract 35337
Hydrology Study
developed condition peak flow rate of Area 3. It follows, consequently, that
no storm mitigation is required for this drainage area. Tables 2 and 3
provide a complete summary of the rational method analysis for each
drainage area.
Area "L" (JDA Area
Area "L" is a drainage area in the post—developed condition that is
tributary to the adjacent downstream property to the north, namely South
Shore (see Figure 6). Under the Stage 1 condition, the area is comprised
largely of natural area with manufactured slope area. Under the Ultimate
condition, the area is comprised of one—quarter acre residential and estate
lot residential developments. The comparable drainage area in the pre—
developed, or existing condition is Area 5.
Since, Area "L" is impacted differently under each of the Stage 1 and
Ultimate scenarios, this study evaluates the drainage area under both
scenarios in order to determine the more critical condition. In short, the
Stage 1 developed condition will generate a lower tributary area than the
Ultimate developed condition will generate at the drainage area's outlet
point. Both of these conditions exceed the tributary area in the existing
condition. Under the Stage 1 scenario, the drainage course of Area "L" is
released at the north Spyglass Ranch boundary at the existing drainage
course that continues northerly onto the South Shore property. Under the
Ultimate condition, the developed condition storm flows from this drainage
area will connect to the South Shore storm drain system to be conveyed to
the South Shore drainage basin.
Due to topographical and other constraints, Area "L" is resolved in
the JDA by a drainage acceptance agreement on the part of South Shore
and to the benefit of Spyglass Ranch. In other words, it is mutually
agreed upon that there is no requirement for Spyglass Ranch to mitigate
for any incremental increase in runoff due to development that may enter
the South Shore property as a result of Spyglass Ranch developing its
property. The JDA stipulates that South Shore will accept all of the
tributary developed area from Spyglass Ranch. South Shore will convey and
provide the necessary water quality treatment to these storm flows prior to
the waters being discharged to Wasson Canyon Creek.
Area "M"
Area ''M" is a drainage area located along a portion of the Spyglass
Ranch south property line in the post—developed condition that is tributary
to the adjacent downstream properties to the south. For the most part,
this drainage area is comprised of manufactured slope area. The
comparable drainage areas in the pre—developed, or existing condition are
Areas 10 and 11. Area "M" developed condition drainage area produces a
lower tributary drainage area when combined and compared to the
correlating existing condition drainage areas. The rational analysis
indicates that the total developed condition peak flow rate of Sub—Area "M"
is less than half that of the total pre—developed condition peak flow rate
of Areas 10 and 11. It follows, consequently, that no storm mitigation is
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