Flood Risk Reduction O&M
Planning for the flood risk reduction projects and system proposals in the LA River Master Plan Update is critical for ensuring the physical feasibility and future success of projects along the river. The USACE and the LACFCD have a combined responsibility in performing operations and maintenance of flood facilities to manage flood risk along the LA River and its tributaries. Clear delineation, tracking, and enforcement of operations and maintenance responsibilities by other agencies for adjacent and overlapping facilities, such as recreational amenities, are critical for ensuring that crucial operations and maintenance is performed at all pertinent locations. Increased coordination between the operations and maintenance entities along the river could enhance efficiencies in comprehensively maintaining the physical functionality of the flood management systems, especially as projects are proposed along the reimagined river.
Flood facility operations and maintenance includes inspections and repairs to elements such as:
Primary operations and maintenance concerns for the structural concrete and grouted riprap-lined channels includes cracking, separation of joints, concrete spalling, vegetation, and uplift of invert slabs. These deficiencies can weaken the structure and create a larger operations and maintenance issue if left unaddressed.
Subdrain systems, which consist of networks of pipes, groundwater relief vaults, cleanouts at channel bottoms, and multiple rows of weep holes along channel sides, are typically present to mitigate for potential build-up of water pore pressures underneath and behind channel sides. Making sure these features are maintained and free of debris is critical to the performance of the channels.
There are many side drain outfalls that drain the local sub-watersheds and discharge into the LA River throughout its 51 miles. Oftentimes, they get clogged with debris and vegetation or require structural repairs to the flap gates.
Trash, Sediment, and Non-native
Invasive Vegetation Management
The earthen-bottom portion of the LA River typically accumulates large amounts of trash, sediment, and non-native invasive vegetation. Routine removal of the debris and management of non-native invasive vegetation using best practices is critical to the facility in order to maintain the capacity of the channel. Non-native invasive vegetation removal should follow the patchwork process described in detail in the Narrows channel rehabilitation project example on the flood risk reduction in the narrows page.
This process first establishes refuge habitats based on the range of key wildlife species identified by qualified professionals, such as ecologists. Removal of non-native invasive species would occur with specially trained crews in areas outside of the refuge habitat, installing additional native species. Once these species are established the remaining non-native invasive species may be removed. Vegetation along levees that is not properly installed or maintained can be a hindrance to visual inspections, maintenance access, and emergency flood fighting (if needed). All vegetation planted along levees should be in accordance with prevailing USACE guidelines as outlined in the LA River Design Guidelines (Appendix Volume I).
Additional Flood Risk Reduction O&M Guidelines
Over time, flood risk reduction infrastructure will require replacement. Additionally, a large storm event that causes significant flooding could alter operations, maintenance, and replacement priorities. In these instances, rather than rebuilding infrastructure in the same way for expediency, current practices should be reviewed and adapted to improve resiliency and provide multiple benefits.
Visual inspections should occur at regular intervals (i.e., semi-annually) in addition to after a large storm event to ensure that the flood risk reduction infrastructure can continue to perform as intended. A visual inspection program is important to identify deficiencies and establish operations and maintenance priorities.
Because the current operations and maintenance responsibility for the LA River falls on both the LACFCD as well as the USACE, the operations and maintenance budget for the LA River system comes from multiple sources. In California, studies of various river systems have shown an average annual operations and maintenance cost per urban levee mile to be $54,000 (in 2019). National examples from the USACE reach as high as $75,000-$100,000 (in 2019) per mile per year for urban and rural levees. These do not include major replacement costs.