HomeMy WebLinkAboutTR 35337 HYDROLOGY REPORT-007 Spyglass Ranch Tract 35337
Hydrology Study
— Design Criteria —
The Spyglass Ranch project is conditioned by the City of Lake Elsinore
to provide a drainage study to identify storm water runoff, to show existing
and proposed onsite and offsite drainage facilities, and to provide the
proper capacity analyses to verify the adequacy of the proposed drainage
improvements. Natural drainage courses traversing the site must be
conveyed through the site, or should be collected and conveyed in such a
manner that is approved by the City Engineer. All offsite drainage, if
different from historic drainage patterns, shall be conveyed to a public
facility, or accepted by an adjacent property owner by a letter of drainage
acceptance, or conveyed to a drainage facility within an easement.
Furthermore, the drainage system shall be designed to ensure that
runoff from a 10—year storm event of 6 hour or of 24 hour durations
under the developed condition is equal to or less than the runoff under
the existing conditions of the same storm frequency. Both the 6 hour and
the 24 hour storm durations shall be analyzed to determine the onsite
detention basin capacities necessary to accomplish the desired results.
Onsite peak flow rates for the 10—year storm event are to be managed
at or below the curb line; peak flow rates for the 100—year storm event
are to be managed within the right—of—way (R/W) limits. If these limits
are exceeded, underground storm drain facilities must be provided to lower
the water surface levels in the roadway to or below the maximum indicated
levels.
Water quality treatment and conveyance is to be provided in accordance
with NPDES requirements to be implemented per the Regional Water Quality
Control Board standards and guidelines for the Santa Ana Watershed. The
required water quality treatment volumes and basin capacities are
determined per the City's WQMP handbook (worksheets included in this
report) and are to be consistent with the approved Spyglass Ranch
Preliminary WQMP. Water quality basins must provide an outlet designed to
retain a minimum of half of the water quality design volume for a
minimum of 24 hours and the remaining water quality design volume for a
minimum of 48 hours, but no longer than 72 hours.
Overall, the project site must be designed to safely convey the 100—Year
storm event through the site should failure of the underground storm drain
system occur. Any further criteria for this report is provided by and
based on the RCFCWCD hydrology manual.
— Scope of Report —
The purpose of this study is to calculate the storm water runoff
associated with the proposed development as necessary to satisfy the City's
conditions and requirements for the drainage study. Results from this
study will be used to (1) provide the design flow rates that the storm
drain system is designed to manage, and (2) analyze the increase runoff
due to development and determine the amount of mitigation where
necessary. The results from this study will be used to size and/or confirm
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