20221676 Ver 1_More Info Received_20230217

Response to DWR Request for Additional Information
1. The stream is reported as approx.. 3 feet wide and the culvert widths as 12' in total
width. Culverts should be designed and installed in such a manner that the original
stream patterns and profiles are not altered and allow for aquatic life movement during
low flows. The dimension, pattern, and profile of the stream above and below a pipe or
culvert shall not be modified by widening the stream channel or by reducing the depth of
the stream in connection with the construction activity. The width, height, and gradient
of a proposed culvert shall be such as to pass the average historical low flow and spring
flow without adversely altering flow velocity. If the width of the culvert is wider than the
stream channel, the culvert shall include multiple boxes/pipes, baffles, benches and/or
sills to maintain the natural width of the stream channel. If multiple
culverts/pipes/barrels are used, low flows shall be accommodated in one culvert/pipe
and additional culverts/pipes shall be installed such that they receive only flows above
bankfull.
We were remiss in our reporting of the stream width. Although the stream within the
golf course portion of the site is quite incised with an average width of approximately 3
feet, the balance of the stream before it enters the existing culvert is approximately
11.5 feet wide within the wooded portion of the site, southwest of the existing culvert,
and the stream width is approximately 10 feet wide as it enters the existing culvert. See
image below.
Furthermore, the existing culvert appears to have the base of the roadway pavement
structure directly on top of the culvert. Corrugated metal pipe culverts are generally
recommended to have a minimum of two feet of soil above the culvert to distribute
loads, so the lack of cover for the existing culvert creates structural risks.
If you are unable to modify the culvert design to use multiple culverts to accommodate
stormflows then please redesign the culvert to include structures such as baffles that will provide
for normal baseflow widths at low flow conditions.
2. The riprap dissipator at the outlet of the culvert appears to be designed to be much wider than
the stream channel. As noted above, it is required that you provide a design that maintains the
normal dimension, pattern and profile of the stream through this section. Please provide plans
that clearly detail how a normal stream channel pattern will be maintained through the riprap
apron.
Due to the stream velocity during storm events, the plunge pool is necessary to
dissipate the energy to negate further downcutting of the stream and erosion.