11 Dec 2024

Numerical Modeling of Supercritical Flow in the Los Angeles River: Part II: Existing Conditions Adaptive Hydraulics Numerical Model Study

Abstract: The Los Angeles District of the US Army Corps of Engineers is assisting the City of Los Angeles with restoration efforts on the Los Angeles River. The city wishes to restore portions of the channelized river to a more natural state with riparian green spaces for both wildlife and public recreation usage. The Los Angeles River provides an important role from a flood-control perspective, and functionality needs to be preserved when contemplating system modifications. This report details the development of an Adaptive Hydraulics numerical model capable of modeling this complex system consisting of both subcritical and supercritical flow regimes. The model geometry was developed to represent the existing conditions system for future usage in quantifying the impact associated with proposed restoration alternatives. Due to limited hydraulic data in the study area, an extensive model validation to observed data was not possible. A model was developed and simulated using the most appropriate input parameters. Given the lack of measured data for model validation, an extensive number of sensitivity simulations were completed to identify the most impactful parameters and quantify a reasonable level of confidence in the model results based on the uncertainty in the model inputs.

31 Jul 2024

Reservoir Sediment Deltas of the Southwestern United States: Challenges and Opportunities for Riparian Vegetation Management

Purpose: This technical note summarizes methods used to identify 58 reservoir sediment deltas in the Southwestern United States and California, behind 47 different dams, with potential regional importance as breeding or migratory stopover habitat for three species of riparian vegetation–dependent birds listed under the Endangered Species Act[1]: least Bell’s vireo (LBVI) (Vireo bellii pusillus), southwest willow flycatcher (SWFL) (Empidonax traillii extimus), and yellow-billed cuckoo (YBCU) (Coccyzus americanus). Information on inflow streams, drainage area, and management authority are provided for each delta. This technical note recommends follow-up research on the temporal dynamics of vegetation colonization, growth, and mortality on these deltas to explore the potential value of these geographically widespread hydrogeomorphic features on arid-land rivers for the conservation of riparian vegetation–dependent birds.

20 Mar 2023

Numerical Modeling of Supercritical Flow in the Los Angeles River: Part I: Adaptive Hydraulics Numerical Modeling of the 1943 Physical Model

Abstract: The Los Angeles District of the US Army Corps of Engineers is assisting the City of Los Angeles with restoration efforts on the Los Angeles River. The city wishes to restore portions of the channelized river to a more natural state with riparian/vegetative green spaces for both wildlife and public recreation usage. The Los Angeles River provides an important role for the City of Los Angeles from a flood-control perspective, and functionality needs to be preserved when contemplating system modifications. This report details the development of an Adaptive Hydraulics (AdH) numerical model capable of representing this complex system consisting of both subcritical and supercritical flow regimes. Due to limited hydraulic data in the study area, an extensive model validation to observed data was not possible. To bridge the data gap, a numerical model was developed from a previously completed physical model study with extensive quantitative measurements and qualitative reports of hydraulic conditions. This approach allowed engineers to evaluate the effectiveness of the AdH model in representing this complex hydraulic system along with determining the best methodology to accurately represent the existing conditions. This study determined appropriate model parameters that will be utilized in further numerical modeling efforts to evaluate system modifications associated with restoration efforts.