HomeMy WebLinkAboutTR 35337 HYDROLOGY REPORT-012 Spyglass Ranch Tract 35337
Hydrology Study
purposes of this report. It is noteworthy that the ultimate condition does
not consider any interim offsite grading into the South Shore project. The
"Developed Condition Hydrology Map - Ultimate Condition" depicts this lot
configuration and grading scenario.
It is important to note that three of the thirteen developed drainage
areas presented in this study are impacted differently under each of the
Stage 1 and Ultimate scenarios. Accordingly, two sets of computations are
provided for the rational analysis for these three areas - one for the
Stage 1 condition and the other for the Ultimate condition. The other ten
drainage areas are essentially the same under either scenario.
Basins
Spyglass Ranch supports three drainage basins that serve as either
water quality basins, storm mitigation facilities, or both. See "Figure 3:
Onsite Basins." The basins are designed to be in compliance with RCFCD
standards and guidelines and are briefly described below. Detail basin
routing computations and water quality design worksheets can be found in
the Appendix of this report and in the Spyglass Ranch Water Quality
Management Plan (WQMP).
Basin #1 is an off-line, single purpose water quality infiltration
basin. The primary basin area plus the forebay area have an overall
volume capacity of about 100,600 cubic feet, or 2.3 acre-feet. The basin is
designed to treat about 53 acres of development. A bifurcation structure
at the storm drain main line will divert only the required water quality
volume from the main line and into the basin. Storm flows are designed
to bypass the basin and discharge directly into the existing culvert located
in Camino Del Norte. A relief underdrain and emergency overspill
structure is provided for the basin in case of minor storm flow escape into
the basin from the mainline and in case of infiltration failure.
Basin #2 is an in-line, dual purpose extended detention basin. The
primary basin area plus the forebay area have an overall volume capacity
of about 252,000 cubic feet, or 5.8 acre-feet. The basin is designed to
mitigate and treat about 69 acres of development. All tributary storm flows
from the storm drain system will be discharged into the basin. The basin
is designed to treat the first flush flows for water quality and mitigate the
higher storm flows with the use of a control basin outlet valve. The basin
outlet pipe located in Camino Del Norte will connect and discharge the
mitigated flows into the existing RCB culvert located about 700 feet
downstream of the basin. The basin is designed to mitigate the higher
storm flows such that the total post-developed flow rate generated from
Spyglass Ranch that enters the existing RCB culvert does not exceed the
approved flow rate in the existing RCB culvert. An emergency overspill
structure is provided for the basin in case of an outlet structure failure.
Basin #3 is an in-line, dual purpose extended detention basin. The
primary basin area plus the forebay area have an overall volume capacity
of about 103,000 cubic feet, or 2.4 acre-feet. The basin is designed to
mitigate and treat 28 acres of development. All tributary storm flows from
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