ATWATER VILLAGE — The U.S. Army Corps of Engineers is scheduled to start installing temporary barriers along an approximately 3-mile stretch of the L.A. River this week. The intent is to raise the height of the channel and reduce the risk of flooding in the Atwater Village area during El Niño rains. Why are these barriers being placed on this stretch of the river? How long will it take to build? The Eastsider posed these and other questions to corps spokesman Jay Field.
Where along the river will the barriers be placed?
It begins in the north roughly at W. Broadway and continues roughly to the California 2 Freeway.
Why did this stretch of the river need extra protection?
Corps experts routinely evaluate flood risk management capabilities of the LA River as part of their winter storm inspections. In light of the likelihood of greater than average rainfall associated with El Niño weather conditions, further scrutiny of Corps structures and facilities was undertaken. The evaluation has indicated unacceptable levels of risk given anticipated rain fall events lasting through this spring. To address those elevated levels of risk, the Corps is implementing risk reduction measures which include placement of temporary protective barriers along the top of the riverbank.
Why is this section of the river more vulnerable than others?
It’s a matter of channel capacity. The original design capacity for that reach of the LA River was 78,000 cfs (cubic feet per second). Our evaluation showed the existing capacity averaging roughly 40,000 cfs due to vegetation growth. With the placement of the temporary protective barriers, we will restore capacity to an average of roughly 60,000 cfs.
Was the river close to overflowing in this section last week?
Not even close! During last week’s storm events, we observed water levels reaching only about one-third of the channel capacity.
How high is the current flood control channel?
Height varies with width in order to achieve the design flow conveyance capacity.
How high are the HESCO barriers?
The barriers we received come in two heights, 3-feet high and 4-feet high. They are 3 X 3, but come in sections of 15 linear feet (five 3 X 3 baskets connected together).
Are they filled with sand, gravel, etc?
They are filled with earthen material and, in our case, will be filled with sand.
How much does each hold?
Each 3 X 3 X 3 barrier holds approximately 27 cubic feet of material. The 3 X 3 X 4 barrier holds approximately 36 cubic feet.
Where will the barriers be placed? Will they be on both banks of the river?
The barrier will be placed immediately adjacent to the edge of the channel so as to minimize its footprint and impacts to the maintenance road. Mostly one bank, but there are a few spots where barriers will be placed on both banks.
When will the barrier be completed?
Temporary protective barrier installation should be complete within a month.
Have these kinds of barriers been used before in Southern California by the corps?
Our district has not used them before in Southern California, but the Corps has used them in the Midwest, in places like Fargo, N.D., and various locations along the Mississippi River.
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