Posted on February 5, 2024
LOS ANGELES — Winter in California is still here, which means cooler temperatures, increased precipitation and higher chances of flooding — something the U.S. Army Corps of Engineers prepares for on an annual basis.
The LA River is the backbone of the Los Angeles County Drainage Area system that has held floodwaters at bay for nearly a century.
LEADERS ADVOCATE FOR SAFETY
Seventeen historic floods occurred between 1815 to 1938, devastating local communities and resulting in loss of life and damage to critical infrastructure. Decisions were made by local leaders at the time to channelize the river to allow the growing population to live safely within its flood plain.
Federal funds were allocated through the Flood Control Act of 1936 to assist Los Angeles County in developing and expanding flood-control infrastructure, which included channelizing 52 miles of the Los Angeles River between 1936 and 1959.
The new channel protected thousands of people and their property; however, the newly strengthened river needed frequent maintenance to ensure an optimal level of protection. In various segments, the river was designed to carry flows up to a 50-year event.
PARTNERS IN FLOOD-RISK MANAGEMENT
The Los Angeles County Drainage Area, including the Los Angeles River, is operated, maintained and managed in various areas by multiple entities, including the Corps, Los Angeles County and the City of Los Angeles.
The channel takes on a different look in various areas of the river, depending on the engineering design and geographical constraints. In most places, there are two different channel styles — rectangular or trapezoidal concrete/grouted stone with a low-flow channel and a trapezoidal soft-bottom channel with grouted stone/concrete levees.
However, in what’s known as the Glendale Narrows area, concrete trapezoidal walls hover over a “soft bottom” channel. This area is about 7.4 miles long and covers about 122.5 acres, expanding through four local communities — Glendale, Atwater Village, Elysian Park and Los Angeles.
GLENDALE NARROWS — CHALLENGES ALONG RIVER
Maintenance in the Glendale Narrows is more challenging than in other areas, and the Corps has been engaged in a multi-year effort to return the area to maximum capacity. The soft-bottom channel was preserved in this location due to the high-water table. Water in this area feeds lush growth, providing habitat to native and invasive species.
Plant growth can provide good ecological habitat, but it also chokes channel capacity. And, some invasive vegetation is very challenging to clear. For example, Giant Reed, or Arundo Donax, can grow to more than 30 feet tall with a deeply set rhizome root that must be dug up.
Additionally, the dense vegetated areas trap sediment, trash and debris that must be removed. The Corps removes select non-native vegetation and performs other work, but only after undertaking required environmental consultations with other state and federal agencies. This can be a time-intensive effort and requires designing project work around certain environmentally friendly windows of time.
PROMOTING LOCAL BUSINESSES, ECONOMIC GROWTH
The Corps provides ongoing maintenance in its area of responsibility. With our most recent contract, the Corps awarded a federal maintenance service contract to a local women and veteran-owned small business in Southern California, with the goal of not only promoting small business growth in Los Angeles, but also hiring a company that understands the challenges along the river.
The company employs 18 maintenance personnel and supervisors and provides monthly services, including trash and debris removal, non-native vegetation management, concrete and sediment debris removal and pipe video inspections.
Additionally, at the end of fiscal year 2023, the Corps awarded a $13.5-million invasive species and sediment management contract for the Glendale Narrows. Work will consist of excavating 100,400 cubic yards of sediment and non-native vegetation as part of a multi-year plan to restore the as-built capacity of the soft-bottom section of the Los Angeles River.
WORK AHEAD IN 2024
The work of the Corps and its contractors continues as we prioritize the following:
- Removal of concrete damaged from recent rain events downstream of Los Feliz Boulevard
- Debris removal and cleanup from more than 100 homeless encampments
- Monitoring 35 additional encampments for flood-risk (notifying agencies to help move people out of harm’s way in the event of a storm)
- Removal of sediment on concrete surfaces of the channel
- Disposal of non-native vegetation on a weekly basis
- Inspection and assessment of 38 storm and subdrain pipes, and,
- Removal of graffiti along 250,000 square feet of the channel on an annual basis.
In collaboration with its local, county and state partners, the LA District’s priority is to ensure the LA River operates as designed during storm events, to protect the lives and property of those who live, work and recreate along its banks. This ongoing effort is part of the LA District’s mission of providing engineering solutions that respond to the needs of the nation, the environment and the communities it serves.
