Thermal Suitability of the Los Angeles River for Cold Water Resident and Migrating Fish Under Physical Restoration Alternatives

Anthropogenic development has adversely affected river habitat and species diversity in urban rivers, and existing habitats are jeopardized by future uncertainties in water resources management and climate. The Los Angeles River (LAR), for example, is a highly modified system that has been mostly channelized for flood control purposes, has altered hydrologic and hydraulic conditions, and is thermally altered (warmed), which severely limits the habitat suitability for cold water fish species. Efforts are currently underway to provide suitable environmental flows and improve channel hydraulic conditions, such as depth and velocity, for adult fish migration from the Pacific Ocean to upstream spawning areas. However, the thermal responses of restoration alternatives for resident and migrating cold water fish have not been fully investigated. Using a mechanistic model, we simulated the LAR’s water temperature under baseline conditions and future alternative restoration scenarios for migration of the native, anadromous steelhead trout in Southern California and the historically resident Santa Ana sucker. We considered three scenarios: 1) increasing roughness of the low-flow channel, 2) increasing the depth and width of the low-flow channel, and 3) allowing subsurface inflow to the river at a soft bottom reach in the LA downtown area. Our analysis indicates that the maximum weekly average temperature (MaxWAT) in the baseline condition was 28.9°C, suggesting that the current river temperatures would act as a limiting factor during the steelhead migration season and habitat for Santa Ana sucker. The MaxWAT dropped about 3%–28°C after applying all the considered scenarios at the study site, which is 3°C higher than the determined steelhead survival threshold. Our simulations suggest that without consideration of thermal restoration, restoring hydraulic conditions may be insufficient to support cold water fish migration or year-round resident native fish populations, particularly with potential river temperature increases due to climate change.

Fish Upstream Passage through Gauging Stations: Experiences with Iberian Barbel in Flat-V Weirs

The monitoring of river discharge is vital for the correct management of water resources. Flat-V gauging weirs are facilities used worldwide for measuring discharge. These structures consist of a small weir with a triangular cross-section and a flat “V”-shaped notch. Their extensive use is a consequence of their utility in the measurement of both low and high flow conditions. However, depending on their size, local morphology and river discharge can act as full or partial hydraulic barriers to fish migration. To address this concern, the present work studies fish passage performance over flat-V weirs considering their hydraulic performance. For this, radio-tracking and video-monitoring observations were combined with computational fluid dynamics (CFD) models in two flat-V weirs, using Iberian barbel (Luciobarbus bocagei) as the target species. Results showed that fish passage is conditioned by both hydraulic and behavioral processes, providing evidence for scenarios in which flat-V weirs may act as full or partial barriers to upstream movements. For the studied flat-V weirs, a discharge range of 0.27–8 m3/s, with a water drop difference between upstream and downstream water levels lower than 0.7 m and a depth downstream of the weir of higher than 0.3 m can be considered an effective passage situation for barbels. These findings are of interest for quantifying flat-V weir impacts, for engineering applications and for establishing managing or retrofitting actions when required.

Fish Upstream Passage Through Gauging Stations. Experiences With Iberian Barbel in Flat-V Weirs

The monitoring of river discharge is vital for the correct management of water resources. A worldwide facility used for measuring discharge are flat-V gauging weirs. These structures consist of a small weir, with a triangular cross-section and a flat “V”-shaped notch. Their extensive use is a consequence of their utility in the measurement of both low and high flow conditions. However, depending on their size, local morphology and river discharge can act as full or partial hydraulic barriers to fish migration. To give answer to this question, the present work studies fish passage performance over flat-V weirs considering their hydraulic performance. For this, radio-tracking and video monitoring observations were combined with computational fluid dynamics (CFD) models in two flat-V weirs, using Iberian barbel (Luciobarbus bocagei) as target species. Results show that fish passage is conditioned by both hydraulic and behavioral processes, providing evidences about the scenarios where flat-V weirs may act as full or partial barriers to upstream movements. For the studied flat-V weirs, a discharge range of 0.27-8 m3/s, with a water drop difference between upstream and downstream water levels lower than 0.7 m and a depth downstream the weir higher than 0.30 m can be considered as an effective passage situation for barbels. These findings are of interest to quantify flat-V weir impacts, for engineering applications and to establish managing or retrofitting actions when required.

Possibility of Hydropower Development: A Simple-to-Use Index

A standardized range system based on carefully selected multi-criteria is proposed in this work to assess the feasibility of hydropower implementation. A thought process has been developed as a simple-to-use and easy-to-understand methodology. Today, due to the broad concern for the natural environment, the use of renewable energy sources has become globally popular. Subsequently, such solutions as the application of renewable energy for electricity generation are often considered the most environmentally friendly installations. Unfortunately, no methodology to assess the possibility of hydropower plant realization in either scientific or industry literature has been put forward, and this constitutes a blatant failure. The proposed range system has been designed to use selected information (head, available flow, fish migration, hydrotechnical infrastructure, protected areas, environmental flow, status of surface water body), which is available through a variety of sources that are easy to obtain. From analyzing the advantages and disadvantages of this research method, it was recognized that it is worth propagating and recommending for the practical estimation of the hydropower potential. The author believes that the novel contribution of the paper, which is the innovative range system, will be accepted for common use.

Turning Pools in Stepped Fishways: Biological Assessment via Fish Response and CFD Models

With the aim of building more compact fishways and adapting them to field conditions to improve their location by fish, it is common to use turning pools, reducing the longitudinal development of the construction. However, depending on their design, turning pools may affect the hydraulic performance of the fishway and consequently the fish passage. To study these phenomena, turning pools in a vertical slot and in different configurations of submerged notches with bottom orifice fishway types were assessed. Both types of fishways were studied using numerical 3D models via OpenFOAM, a computational fluid dynamics software, in combination with fish responses, assessed with PIT (Passive Integrated Transponder) tag telemetry for three different species of potamodromous cyprinids in several fishways. Results show differences between the hydrodynamics of straight and turning pools, with lower values in the hydrodynamic variables in turning pools. Regarding fish behavior, the ascent was slower in turning pools but with no effect on passage success and without being a problem for fish migration. This information validates the use of turning pools as a key design component for fishways for studied species.