2016-08 SRR Venue Site Reccomendation Tech Memo 2019-12-06
75410 Gerald Ford Drive, Palm Desert, CA 92211
Office: 760.346.7481 | Direct: 760.341.6117
TECHNICAL M E M O R A N D U M
To: Mr. Bryan McKinney, City Engineer JN: 154969
From: Daniel Koravos, PE
Date: December 6, 2019
Subject: SilverRock Venue Storm Drain Outfall Erosion
Recommendation
The existing 54-inch storm drain discharging onto the SilverRock Venue Site is referenced on the
Avenue 52 Storm Drain Improvements, City of La Quinta Project No. 2005-10 (City of La Quinta
Plan Set No. 05120), prepared by The Keith Companies (TKC), dated July 2005 and revised August
3, 2005. Subsequently, additional plans for The SilverRock Venue Site were prepared by Michael
Baker, dated July 2019 and revised October 22, 2019 indicating storm drain modifications into a
new drainage basin.
The design intent was to cut the existing pipe and flared end section back approximately eighteen
(18) feet and install a new headwall and riprap system. Prior to construction completion, runoff
discharged from the existing storm drain and caused slope erosion. As a result, the flared end
section and a portion of the existing pipe system was undermined and broke off into the bottom
of the basin.
Subsequently, Earth Systems prepared a report entitled “Limited Geotechnical Engineering Report,
SilverRock Park Venue Storm Drain Outfall Erosion/Scour Repair”, dated October 16, 2019, for the City of
La Quinta. The report provided additional detailed information about the soils in the vicinity of the slope
erosion and recommendations. Michael Baker provided additional recommendations in a Technical
Memorandum dated November 5, 2019.
Based on all the new information provided to date, Michael Baker has identified two possible solutions
for the repair of the drainage system to minimize future issues. 1) Restore the existing slope, install the
headwall and construct a grouted riprap channel down the slope into the basin. 2) Extend the existing
pipe to the bottom of the basin, restore the exiting slope and install an energy dissipater at the outlet of
the pipe. Because of the new soils information and recommendations, Michael Baker recommends the
second solution of extending the drainage pipes to the bottom of the basin.