HomeMy WebLinkAboutDune Palms_Attachment A Location Hydraulic Study FormLOCATION HYDRAULIC STUDY FORM
DUNE PALMS ROAD BRIDGE
Dist. 08 Co. Riverside Rte. Local Assistance, City of La Quinta
FPN: BLRKS-5433(014) Bridge No. NA
Floodplain Description:
The Whitewater River Basin is located approximately 100 miles east of Los Angeles. The watershed
drains to the Salton Sea located about 23 miles south of the project site. The tributary area of the
watershed is made up of a broad desert valley (Coachella Valley) between two mountain ranges; the
San Bernardino and Little San Bernardino Mountains form the northeast boundary of the watershed,
the San Jacinto Mountains form the southeast boundary.
Upstream from the vicinity of Washington Street (Point Happy) the channelized section of the
Whitewater River is referred to as the Whitewater River Storm Water Channel (WWRSC);
downstream to the Salton Sea, this channelized section is named the Coachella Valley Storm Water
Channel (CVSC).
The drainage area tributary to the CVSC at the proposed Dune Palms Road Bridge is
approximately 788 sq. mi. (USCOE 1980)i. The mean seasonal precipitation in the area tributary to
the Dune Palms Road crossing varies from 44 inches at San Gorgonio Mountain to about 3 inches
at the crossing. The watershed is shown in Error! Reference source not found.. The channel
discharge-frequency graph is shown on Error! Reference source not found.
1. Description of Proposal (include any physical barriers i.e. concrete barriers, soundwalls, etc.
and design elements to minimize floodplain impacts)
The purpose of this project is to replace the existing Dune Palms Road Low-Water (“at grade”)
crossing with a bridge over the CVSC in the City of La Quinta, California at the location shown on
Error! Reference source not found.. The channel crossing is located north of Highway 111
between Adams Street and Jefferson Street.
The new bridge structure will be located at the existing low water crossing and consists of four spans
(2 at 105-feet and 2 at 135-feet) for a total bridge length of 480-feet. Three piers will be located
within the channel. The abutments are located out of the anticipated 100-year flood flow elevation.
The bridge design meets the HBRR program hydraulic design criteria.
Following the construction of the bridge and subsequent removal of the existing low-water crossing,
the Base Flood Elevation will be lowered by approximately five feet. The project will not increase
flood flow downstream of the CVSC.
2. ADT: Current (2013) 9,457 Projected (2035) 16,547
3. Hydraulic Data: Base Flood Q100=43,000 CFS WSE100 = 51.7 FT
The flood of record, if greater than Q100:
Q= NA WSE= NA
Overtopping flood Q= >110,000 CFS WSE= 66 FT +/-
Are NFIP maps and studies available? YES X NO
4. Is the highway location alternative within a regulatory floodway?
YES X NO
5. Attach map with flood limits outlined showing all buildings or other improvements within the
base floodplain. See attached Hydrology & Hydraulic Study report.
Potential Q100 backwater damages:
A. Residences? NO X YES
B. Other Bldgs? NO X YES
C. Crops? NO X YES
D. Natural and beneficial
FLOODPLAIN VALUES? NO X YES
6. Type of Traffic:
A. Emergency supply or evacuation route? NO YES X
B. Emergency vehicle access? NO YES X
C. Practicable detour available? NO YES X
D. School bus or mail route? NO YES X
7. Estimated duration of traffic interruption for 100-year event hours: 0
8. Estimated value of Q100 flood damages (if any) – moderate risk level.
A. Roadway $ 0
B Property $ 0
Total $ 0
9. Assessment of Level of Risk Low X
Moderate
High
For High Risk projects, during design phase, additional Design Study Risk Analysis may be
necessary to determine design alternative.
Signature – Hydraulic Engineer Date 2/19/15
(Md. Wahiduzzaman, RCE C049838)
Bengal Engineering, Inc.
Is there any longitudinal encroachment, significant encroachment, or any support of incompatible
floodplain development? NO X YES
If yes, provide evaluation and discussion of practicability of alternatives in accordance with 23 CFR
650.113
Information developed to comply with the Federal requirement for the Location Hydraulic Study
shall be retained in the project files.
Signature – Project Engineer Date 2/24/15
(Item numbers 1,2,6,8)
i USACE – Whitewater River Basin Feasibility Report for Flood Control and Allied Purposes, San
Bernardino and Riverside Counties, California, Appendix 1 Hydrology, May 1980