HomeMy WebLinkAboutTR 35337 HYDROLOGY REPORT-011 Spyglass Ranch Tract 35337
Hydrology Study hI ^
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as Area 2. PM 30985 shows that it accepts an approved flow rate from
Spyglass Ranch at their common boundary of 128 cfs. This runoff is
depicted per the PM 30985 improvement plans to be intercepted in a 71x3'
RCB headwall inlet structure that is located at the common property line.
Thirdly, there is a drainage area whose drainage course crosses at
multiple locations the portion of the north boundary adjacent to the South
Shore development. The area tributary to this drainage course is identified
as Area 4. It can be observed that the primary drainage course in Area 4
originates within Spyglass Ranch (at node 401), then crosses the north
boundary into South Shore (at node 402), then re-enters Spyglass Ranch
(near node 403), and finally crosses the north boundary a third time into
South Shore (at node 406) before confluencing with another drainage course
(at node 407) within the South Shore property that drains westerly. It is
noteworthy that a special condition is presented by this drainage area that
will be further addressed under the Post-Developed Section of this report.
Post-Developed Condition -
Stage 1 and Ultimate Condition Scenarios
This study takes under consideration two different construction scenarios
for the Spyglass Ranch development. Spyglass Ranch is proposed to be
graded in two stages, as depicted in Figure 2. Stage 1 is comprised of the
first five of the seven tract phases (i.e. 35337-1, -2, -3, -4, and -5) and
includes the vast majority of the single family residential lots along with
the park site and the higher-density development parcels. Since
construction of Stage 1 can be completed mostly independent of South
Shore commencing work, there is an interim condition construction scenario
that is plausible, and thus used as one of the two overall post-developed
models evaluated in this study. This interim condition occurs after the
Stage 1 grading is complete and South Shore is not yet constructed. At
this stage, there is significant offsite grading that is necessary for Spyglass
Ranch in order to complete the road and lot construction in the vicinity of
its common boundary with South Shore. This condition is called "Stage 1"
for purposes of this report. It is noteworthy that Stage 1 also includes the
construction of the water tank site and the appropriate access road to it.
The "Developed Condition Hydrology Map - Stage 1" depicts this lot
configuration and grading scenario.
Stage 2 is comprised of the last two of the seven tract phases (i.e.
35337-6, -F) that includes single family residential lots and several larger
estate residential lots. Since construction of Stage 2 is dependent on South
Shore for access, it is plausible that Stage 2 will be constructed either
concurrent with or after South Shore develops. Thus, the Stage 2 grading
scenario is evaluated under the ultimate (i.e. built out) condition for both
projects and used as the second of the two overall post-developed models
evaluated in this study. This condition occurs after the Stage 2 grading is
complete and South Shore is constructed in its entirety. At this stage,
secondary access is available for the Spyglass Ranch final phases at its
common boundary with South Shore. This condition is called "Ultimate" for
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