scholarly journals Environmental Restoration Of Concrete Flood-Control Channels

2021 ◽  
Author(s):  
Celia W.M. Fan
Keyword(s):  
Hong Kong ◽  
Physical Model ◽  
Flood Control ◽  
Control Function ◽  
Flow Channel ◽  
Design Approach ◽  
Low Flow ◽  
Stream Assessment ◽  
Pilot Site ◽  
Rivers And Streams

Many rivers and streams throughout the world in the past century were severely affected by human activities including water extraction, watershed land use changes, power generation, dam and levee construction. In highly urbanized cities, engineering practices advocate straightening, enlarging, and converting the natural rivers and streams into concrete channels to minimize flooding and erosion problems. These engineering design approaches destroy the natural equilibrium of the fluvial systems and eliminate the aquatic and riparian species in the watercourse. The objective of this research is to develop a general stream restoration design approach for flood control concrete channels in highly urbanized areas. The restoration goals are: 1) to create a natural and self-sustainable river system in order to re-establish the aquatic species on the flood control channel; 2) to provide appropriate in-stream covers, pools and riffles features for fish spawning and rearing; and 3) to maintain the flood control function after stream restoration. There are four phrases involved in the design methodology of flood channels restoration: 1) identification of restoration goals, 2) stream assessment on the existing condition; 3) modification and verification of the low-flow channel design based on stream assessment findings; and 4) confirmation of the original flood control function. Yuen Long Nullah in Hong Kong will be used as a pilot site study to demonstrate the design framework. Meanders and deflectors will be applied to the low-flow channel modification design. A physical model representing an actual 2-metre wide meander channel section of the low-flow channel was constructed and experimented at The Hong Kong Polytechnic University’s Hydraulics Laboratory. A numerical sediment transport model using the CCHE2D program was used to adjust the modification design and verify the flood control function. The pilot site has been tentatively demonstrated the restoration design approach developed in this research where deflectors are a major factor on pools creation. Moreover, a single deflector located along the inner curvature of the meander section with 1/3 contraction ratio is proved to be the best design using the physical model. The numerical model using the CCHE2D program showed that the 7-block system can be used to model a deflector with porosity of 40%. Numerical results also demonstrated that the bed material will not be totally flushed out after a severe thunder storm.

scholarly journals Environmental Restoration Of Concrete Flood-Control Channels

2021 ◽  
Author(s):  
Celia W.M. Fan
Keyword(s):  
Hong Kong ◽  
Physical Model ◽  
Flood Control ◽  
Control Function ◽  
Flow Channel ◽  
Design Approach ◽  
Low Flow ◽  
Stream Assessment ◽  
Pilot Site ◽  
Rivers And Streams

Many rivers and streams throughout the world in the past century were severely affected by human activities including water extraction, watershed land use changes, power generation, dam and levee construction. In highly urbanized cities, engineering practices advocate straightening, enlarging, and converting the natural rivers and streams into concrete channels to minimize flooding and erosion problems. These engineering design approaches destroy the natural equilibrium of the fluvial systems and eliminate the aquatic and riparian species in the watercourse. The objective of this research is to develop a general stream restoration design approach for flood control concrete channels in highly urbanized areas. The restoration goals are: 1) to create a natural and self-sustainable river system in order to re-establish the aquatic species on the flood control channel; 2) to provide appropriate in-stream covers, pools and riffles features for fish spawning and rearing; and 3) to maintain the flood control function after stream restoration. There are four phrases involved in the design methodology of flood channels restoration: 1) identification of restoration goals, 2) stream assessment on the existing condition; 3) modification and verification of the low-flow channel design based on stream assessment findings; and 4) confirmation of the original flood control function. Yuen Long Nullah in Hong Kong will be used as a pilot site study to demonstrate the design framework. Meanders and deflectors will be applied to the low-flow channel modification design. A physical model representing an actual 2-metre wide meander channel section of the low-flow channel was constructed and experimented at The Hong Kong Polytechnic University’s Hydraulics Laboratory. A numerical sediment transport model using the CCHE2D program was used to adjust the modification design and verify the flood control function. The pilot site has been tentatively demonstrated the restoration design approach developed in this research where deflectors are a major factor on pools creation. Moreover, a single deflector located along the inner curvature of the meander section with 1/3 contraction ratio is proved to be the best design using the physical model. The numerical model using the CCHE2D program showed that the 7-block system can be used to model a deflector with porosity of 40%. Numerical results also demonstrated that the bed material will not be totally flushed out after a severe thunder storm.

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

2022 ◽  
Vol 9 ◽  
Author(s):  
Reza Abdi ◽  
Ashley Rust ◽  
Jordyn M. Wolfand ◽  
Kristine Taniguchi-Quan ◽  
Katie Irving ◽  
...  
Keyword(s):  
Los Angeles ◽  
Flood Control ◽  
Cold Water ◽  
Flow Channel ◽  
Low Flow ◽  
Fish Migration ◽  
Santa Ana ◽  
Los Angeles River ◽  
Hydraulic Conditions ◽  
Water Fish

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.

scholarly journals Comparison of Large Woody Debris Prototypes in a Large Scale Non-flume Physical Model

2018 ◽  
Vol 40 ◽  
pp. 05010
Author(s):  
Brian Perry ◽  
Colin Rennie ◽  
Andrew Cornett ◽  
Paul Knox
Keyword(s):  
Physical Model ◽  
Flood Control ◽  
Large Scale ◽  
Woody Debris ◽  
Water Levels ◽  
Mitigation Strategies ◽  
Large Woody Debris ◽  
Debris Accumulation ◽  
The Impact ◽  
The City

Due to excessive rainfall in June of 2013, several rivers located in and near the City of Calgary, Canada experienced significant flooding events. These events caused severe damage to infrastructure throughout the city, precipitating a renewed interest in flood control and mitigation strategies for the area. A major potential strategy involves partial diversion of Elbow River flood water to the proposed Springbank Off-Stream Storage Reservoir. A large scale physical model study was conducted to optimize and validate the design of a portion of the new project. The goals of the physical model were to investigate diversion system behaviors such as flow rates, water levels, sediment transport and, debris accumulation, and optimize the design of new flow control structures to be constructed on the Elbow River. In order to accurately represent the behavior of debris within the system due to flooding, large woody debris created from natural sources was utilized in the physical model and its performance was compared to that of debris of the same size fabricated from pressed cylindrical wood dowels. In addition to comparing the performance of these two debris types, the impact of root wads on debris damming was also investigated. Significant differences in damming behavior was shown to exist between the natural debris and the fabricated debris, while the impact of root wad on damming affected the dam structure and formation. The results of this experiment indicate that natural debris is preferred for studies involving debris accumulation.

scholarly journals One consideration about application of the rubble bed protection work concrete block to fishway works and flood control function

2012 ◽  
Vol 68 (7) ◽  
pp. III_227-III_237
Author(s):  
Takahide HONDA ◽  
Shuichi ASARI ◽  
Junichi AKINO ◽  
Koji TAKAZAWA ◽  
Kiyomitsu TAKASHIMA ◽  
...  
Keyword(s):  
Flood Control ◽  
Control Function ◽  
Concrete Block ◽  
Bed Protection

scholarly journals Streamflow Characteristics and Changes in Kolyma Basin in Siberia

2008 ◽  
Vol 9 (2) ◽  
pp. 267-279 ◽  
Author(s):  
Ipshita Majhi ◽  
Daqing Yang
Keyword(s):  
Flood Control ◽  
Human Impacts ◽  
Cold Season ◽  
Northern Region ◽  
Low Flow ◽  
Discharge Data ◽  
Dam Impact ◽  
Reservoir Regulation ◽  
Monthly Discharge ◽  
Annual Discharge

Abstract This study documents major changes in streamflow hydrology over the Kolyma watershed due to climatic variations and human impacts. Streamflow seasonal cycles over the basin are characteristic of the northern region, with the lowest runoff in April and peak flow in June. Analyses of monthly flows and trends show that reservoir construction and operation have considerably affected streamflow regimes. Comparisons of mean monthly discharge records between pre- and post-1986 dam periods indicate that the mid–lower basin (downstream of the dam) experienced significant increase in low flows and decrease in peak flows after dam construction. For example, mean monthly flows during the post-dam period at the Ust’-Srednekan station (located 1423 km downstream of the dam) has strongly increased by about 205 m3 s−1 (or 522%–3157%) during December–April, and decreased by 133 m3 s−1 (41%) in June. Long-term monthly discharge data reveal an overall increase in streamflow during low flow seasons; the increase is greater for the stations located downstream of the dam. The Srednekolunsk station (1720 km from dam) shows low flow increase ranging from 130 (43%) to 268 m3 s−1 (454%) during November–April, and high discharge decrease by 2550 to 519 m3 s−1 during June–August in the post-dam era (1986–2000). These changes in flow patterns are mainly caused by reservoir regulation, as reservoirs release water in winter for power generation and store water in summer for flood control. Dam impact on flow regimes and changes are visible along the main river trunk; thus, the cold season discharge increase at the basin outlet is primarily the result of reservoir regulation. Annual discharge records show different changes within the Kolyma basin, with moderate increases in the upper basin and weak decreases in the mid–lower basin. Overall annual discharge near the basin outlet has decreased by 1.5% during 1978–2000. This study emphasizes the importance of human activities (particularly reservoirs) on seasonal and regional hydrology changes and points to the need to further examine natural causes and human impacts over other high-latitude watersheds.

scholarly journals Exploring trade-offs between SDGs for Indus River Dolphin conservation and human water security in the regulated Beas River, India

2021 ◽  
Author(s):  
Andrea Momblanch ◽  
Nachiket Kelkar ◽  
Gill Braulik ◽  
Jagdish Krishnaswamy ◽  
Ian P. Holman
Keyword(s):  
Climate Change ◽  
Flood Control ◽  
Extinction Risk ◽  
Freshwater Ecosystems ◽  
Low Flow ◽  
Conservation Strategies ◽  
Climate Change Scenarios ◽  
Indus River ◽  
Systems Model ◽  
Trade Offs

AbstractIn India’s Indo-Gangetic plains, river flows are strongly altered by dams, barrages and water diversions for irrigation, urban supply, hydropower production and flood control. Human demands for freshwater are likely to intensify with climatic and socio-economic changes, exacerbating trade-offs between different sustainable development goals (SDGs) dependent on freshwater (e.g. SDG2, SDG6, SDG7, SDG11 and SDG15). Freshwater ecosystems and endangered aquatic species are not explicitly addressed in the SDGs, but only nested as targets within SDG6 and SDG15. Thus, there is high risk that decisions to advance other SDGs may overlook impacts on them. In this study, we link a water resource systems model and a forecast extinction risk model to analyze how alternative conservation strategies in the regulated Beas River (India) affect the likelihood of survival of the only remaining population of endangered Indus River Dolphins (IRD) in India in the face of climate change-induced impacts on river hydrology and human water demands, explicitly accounting for potential trade-offs between related SDGs. We find that the frequency of low flow released from the main reservoir may increase under some climate change scenarios, significantly affecting the IRD population. The strongest trade-offs exist between the persistence of IRD, urban water supply and hydropower generation. The establishment of ecologically informed reservoir releases combined with IRD population supplementation enhances the probability of survival of the IRD and is compatible with improving the status of relevant SDGs. This will require water managers, conservation scientists, and other stakeholders to continue collaborating to develop holistic water management strategies.

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