Orestimba Creek Flood Risk Management Project

Update Status: Project Lead update 4/29/16

Project Lead: City of Newman

Potential Project Partners: 
Stanislaus County, Orestimba Creek Flood Control District, USACE

Short Project Description:
Construction of a 4.7-mile chevron levee along east bank of Central California Irrigation District (CCID) Main Canal and a 1-mile cross levee to reduce flood risk to Newman and adjacent agricultural areas, providing a 200-year level of protection. The chevron levee would include 3 feet of freeboard above the mean 200-year water surface elevation.

Long Project Description:
The chevron levee would be constructed parallel to the east bank of the CCID Main Canal. Starting at the Newman Wasteway, the levee would continue north to a location near Lundy Road, at which point the levee alignment would angle diagonally away from the canal toward the northeast for another 0.7 miles to tie in to the CNRR embankment near an existing culvert. This existing culvert would function to reduce the frequency and duration of floodwater ponding on the north side of the levee. The levee would also extend an additional 35 feet east of the CNRR embankment to ensure that floodwaters do not flank the proposed levee. The levee would be approximately 4.7 miles in total length. The proposed levee is higher than roadway elevations at four crossing locations, and a gap in the top portion of the levee is required to meet highway vertical curve safety standards. A slotted abutment would be constructed in the levee on each side of these roadways. During a flood event, stop logs would be placed into the slotted abutments across the roadways. When installed, the stop log structure would be approximately 1 to 3 feet high and would prevent floodwaters from flowing through the gap. This would not interfere with traffic because the roadway to the west of the structure would be flooded when the stop logs were in place. The stop‐log closure structures would be located at four locations where existing roads cross the proposed levee alignment. These road crossings include Shells Road, Draper Road, Orestimba Creek Road, and Stuhr Road. Another gate closure would be constructed where the levee crosses the CNRR railroad embankment. The proposed levee is higher than the railway and a gap in the top portion of the levee is required to prevent interference with the levee grade. An abutment would be constructed in the levee on each side of the railway. During a flood event, floodgates hinged on the abutment would be closed across the railway. When installed, the swing gate structure would be approximately 2 to 3 feet high and would prevent floodwaters from flowing through the gap. This would not interfere with railway traffic because the railway north of the levee would be flooded when the swing gate structure was in place.

Where the levee crosses State Highway 33, the highway would be raised to meet levee design elevations. Highway 33 would be raised over an additional 2000 foot length to account for longer vertical curves necessary to go over the higher levee. Another component of the levee is a seepage berm. The proposed project would also include a railroad embankment protection plan. During small flood events and localized rainfall events, Orestimba Creek floodwater or local runoff would be conveyed to the east side of the railroad embankment through existing drainage culverts. However, the railroad would be overtopped during a large flood event. To mitigate for this condition, the east side of the railroad embankment would require a sand filter and be lined with rock revetment to prevent erosion. Approximately 10 culverts under the CNRR embankment would be extended to accommodate the seepage embankment and erosion protection. New upstream and downstream headwalls would be constructed at each culvert. The railroad embankment protection plan begins where the proposed levee crosses the railroad and ends where the railroad crosses Orestimba Creek. The distance is approximately 2 miles.

Stanislaus County has three low water crossings of Orestimba Creek that are closed every year during normal precipitation. The three low water crossings of Orestimba Creek from west to east are Bell Road, Jorgensen Road, and Eastin Road. Bell Road is the most westerly road and has automatic gates that drop when there is water on the road. This location does not incur as many stranded vehicles as the other two and not resulted in a fatality. The Bell Road crossing is a much shallower crossing than the other two as it does not drop as far down into the creek bottom as the other two crossings due to 3 culverts at low flow channel elevation. The low water crossing at Jorgensen Road has automatic gates that drop when there is water on the road. The channel profile at this location has a much more defined river channel that is approximately 8 to 10 feet lower than the existing top of bank elevation. Jorgensen Road does not have culverts and so any flows here flow over the road. Jorgensen Road has not had fatalities, however, Stanislaus County Public Works has had many dozens of vehicles in the last 20 years try to cross here and subsequently get stranded while Orestimba Creek is flowing. The low water crossing at Eastin Road is the most heavily traveled of the three low water crossings. This location has automatic gates that drop when there is water on the road. This location does have a 24” diameter culvert that carries a minimal amount of water under the road at the low flow condition. This location floods approximately up to 5 feet above the crown of the road. Stanislaus County has had 2 fatalities at this location due to people leaving their stranded vehicles and getting swept downstream in the flood.

Unique Project Characteristics:
None specified

Project Status Planning
Project Cost $44,000,000
Project Timeframe 1-5 years
Cost-sharing Federal contribution of $23,230,000 with non-federal contribution of $21,100,000
Multi-benefit Project Yes
Types of benefits This project would reduce flood risk in the near term by providing protection against the 200-year flood. Note: It may lead to greater future flood risk if further development in the floodplain is spurred by its implementation. The project would also improve institutional support.
Source of Project USACE

Background Information:
Orestimba Creek Flood Risk Management Draft Feasibility Report and EA/IS - http://cityofnewman.com/news-and-information/e-docs.html (see document list under Public Works)

Latitude:  37.329129655

Longitude: -121.04359003