HomeMy WebLinkAboutTR 35337 HYDROLOGY REPORT-009 Spyglass Ranch Tract 35337
Hydrology Study
Design Software suite and recommended by RCFCWCD. Rainfall, loss rates,
AMC requirements, and other such data that is pertinent to the
development of the unit hydrographs are based upon Increased Runoff
Criteria typically required by RCFCWCD.
— Pre—Developed Condition —
By in large, the soil type for the majority of this site has a high runoff
potential, as designated by the U.S. Soils Conservation Service (SCS) as Soil
Groups C and D. These areas are characterized as having a low capacity
to transmit water, thereby resulting in a slow to very slow rate of
infiltration, and a relatively high volume of runoff. There are, however,
some minor areas that are characterized as having moderate infiltration
rates, designated as SCS Soil Group B (ref. RCFCD Hydrology Manual Plate
C-1.41). The appropriate ratio of each soil group is used in the existing
condition model of this study. Another factor that adds to the high
potential for storm runoff due to the existing soil type is that the site
also has poor ground cover. For purposes of these study computations,
poor soil cover is basically defined by SCS as a watershed having less than
fifty—percent of its ground surface covered by tree canopy and brush.
Another factor that will generate a high rate of runoff in the existing
condition is the significant relief across the site. Generally, the lay of the
land flows in a south to southwesterly direction towards Lake Elsinore,
which sits just over one mile downstream of the subject tract. The highest
elevation within the site is approximately 1800 feet MSL and the lowest
elevation is approximately 1300 feet MSL. The existing terrain is
mountainous with significant hill and valley formations. Storm runoff from
the site takes several different local paths from the project site prior to
reaching the Lake, the ultimate discharge point. A number of ridgelines
divide the site into distinct drainage areas that create flow paths in all
directions. Because of this, there are many drainage courses that outlet
across the boundary on all sides of the project.
Yet, since the site is relatively elevated within its vicinity, there are
essentially no substantial offsite flows that are tributary to the site.
Generally speaking, the site's watershed boundary nearly matches the
project boundary with flow patterns that run from onsite to offsite.
However, there are three areas that contain a drainage course that has
multiple project boundary crossings, flowing offsite to onsite and vice versa.
Referencing the Existing Condition Hydrology Map, these areas are identified
as Areas 2, 4, and 12. These drainage areas do not raise a great deal of
concern since the offsite contribution within these sub—areas is relatively
minimal. These drainage areas are discussed further in their post—
developed condition under the following section of this report.
Although the majority of the drainage areas are treated in a standard
manner as they relate to the existing and developed conditions, there are
three edge conditions that are worthy to note. The first is the frontage
along Camino Del Norte, the second is the far west boundary that is
adjacent to Parcel Map (PM) 30985, and the third is the north boundary
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