HomeMy WebLinkAboutTR 35337 HYDROLOGY REPORT-008 Spyglass Ranch Tract 35337
Hydrology Study
the storm drain pipes, catch basins, onsite detention basin volumes and
hydraulic performance, detention basin outflow structures (water quality
control and storm mitigation), and the street flood capacity. This study
considers the conveyance of all the local onsite and tributary offsite
drainage flows for both the ultimate and interim conditions.
This study includes the hydraulic analysis and design of the culvert
system being used in the post—developed condition that is located along
the project frontage on Camino Del Norte. The proposed development is
considered to have no adverse hydraulic impacts on the downstream
conveyance facilities located along the westerly side of the Freeway that
drain northerly. Consequently, analysis of these downstream facilities is
not necessary and is therefore excluded from this study.
The study includes a general evaluation of the Wasson Canyon Basin, a
Municipal Separate Storm Sewer System ("MS4") facility, which is located
downstream and approximately 800 feet from the project's westerly
boundary. The Basin is owned and operated by the Riverside County Flood
Control District (RCFCD) and is to serve as an ultimate discharge point for
a large part of the project's drainage runoff. The purpose of the
evaluation is to confirm that the Basin is not adversely impacted by the
proposed development flows. The Basin Plan referenced in this study is
the Wasson Canyon Channel Stage I RCFCD Project No. 3-0-180.
— Methodology —
Rational method hydrology is implemented to calculate the 100—year and
10—year storm frequency peak flow rates. Drainage areas are determined
and defined using ridgeline boundaries and "link—node" streams. The
rational calculations are performed by Rational Method Riverside County
("RRIV") provided in the Civil Design Software suite, developed by Joseph E.
Bondiman & Associates and recommended by RCFCWCD. Rainfall, loss rates,
and other such data that is pertinent to the rational method calculations
are determined by "RRIV" and summarized within the output files provided
herein. By combining the "link—node" rational method in the 'RRIV"
program with street depth and catch basin capture calculations, the storm
drain pipes and catch basin sizes are determined. These values dictate
the placement and sizing of the underground drainage facilities based upon
the street capacity. This method makes use of "RRIV" for primarily three
values: peak flow rates, time of concentration, and accumulated drainage
area. Values generated by "RRIV" that are neglected and may be found
more accurately, as determined in the hydraulic calculations, include depth
of street flow, street capacity calculations, and catch basin capture
calculations.
Synthetic unit hydrograph modeling is used in accordance with City and
RCFCWCD requirements and guidelines to study the appropriate storm return
frequencies and durations to be mitigated. Mitigation for the necessary
conditions will be achieved thorough detention basins and the use of a
control outlet valve structure. The software employed to compute the unit
hydrographs and basin routing calculations are contained within the Civil
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