Technical guide for the development, evaluation, and modification of stream assessment methods for the Corps Regulatory Program

The U.S. Army Corps Regulatory Program considers the loss (impacts) and gain (compensatory mitigation) of aquatic resource functions as part of Clean Water Act Section 404 permitting and compensatory mitigation decisions. To better inform this regulatory decision-making, the Regulatory Program needs transparent and objective approaches to assess the function and condition of aquatic resources, including streams. Therefore, the Regulatory Program needs function-based stream assessments (1) to characterize a stream’s condition or function, (2) to improve understanding of the impact of a proposed action on an aquatic resource, and/or (3) to inform the development of stream compensatory mitigation tools rooted in stream condition and/or function. A function-based stream assessment can provide regulatory decision makers with the resources to objectively consider alternatives, minimize impacts, assess unavoidable impacts, determine mitigation requirements, and monitor the success of mitigation projects. A multiagency National Committee on Stream Assessment (NCSA) convened to create these guidelines to inform the development of new methods and evaluation of both national-level and regional methods currently in use. The resulting guidelines present nine phases, including rationale and recommendations to facilitate work efforts. The NCSA hopes that this technical guide promotes transparency, technical defensibility, and consistent application of stream assessments in the Regulatory Program.

Environmental Restoration Of Concrete Flood-Control Channels

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.

Environmental Restoration Of Concrete Flood-Control Channels

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.

Spatial Heterogeneity of eDNA Transport Improves Stream Assessment of Threatened Salmon Presence, Abundance, and Location

The integration of environmental DNA (eDNA) within management strategies for lotic organisms requires translating eDNA detection and quantification data into inferences of the locations and abundances of target species. Understanding how eDNA is distributed in space and time within the complex environments of rivers and streams is a major factor in achieving this translation. Here we study bidimensional eDNA signals in streams to predict the position and abundance of Atlantic salmon (Salmo salar) juveniles. We use data from sentinel cages with a range of abundances (3–63 juveniles) that were deployed in three coastal streams in New Brunswick, Canada. We evaluate the spatial patterns of eDNA dispersal and determine the effect of discharge on the dilution rate of eDNA. Our results show that eDNA exhibits predictable plume dynamics downstream from sources, with eDNA being initially concentrated and transported in the midstream, but eventually accumulating in stream margins with time and distance. From these findings we developed a fish detection and distribution prediction model based on the eDNA ratio in midstream versus bankside sites for a variety of fish distribution scenarios. Finally, we advise that sampling midstream at every 400 m is sufficient to detect a single fish at low velocity, but sampling efforts need to be increased at higher water velocity (every 100 m in the systems surveyed in this study). Studying salmon eDNA spatio-temporal patterns in lotic environments is essential to developing strong quantitative population assessment models that successfully leverage eDNA as a tool to protect salmon populations.

Do changes in temperature affect EU Water Framework Directive compliant assessment results of central European streams?

Background Benthic invertebrate communities are an integral and longstanding component of stream biomonitoring. However, multiple stressors driven by global change threaten benthic invertebrate communities. In particular, climate warming is expected to disrupt freshwater ecosystems. While an increasing number of studies have shown changes in benthic invertebrate community composition in response to climate warming, the effect on stream assessments has rarely been investigated. As several community composition metrics are also used in stream assessments, we predicted that climate warming would worsen stream assessment results. Therefore, we used a comprehensive data set of 2865 benthic invertebrate samples taken between 2000 and 2014 from small central European low mountain streams. We examined the effects of changes in temperature on common community and stream assessment metrics. We used 31 metrics covering composition, richness, tolerance and function of communities, of which many are used in various stream assessment schemes. Results Against our expectations, we identified a decreasing air temperature trend of − 0.18 °C over 15 years. This trend was accompanied by significant changes in community composition, for example, increases in species richness and decreases in the community temperature index (CTI). Further, we identified slight concomitant improvements of various globally used stream quality assessment metrics, such as a decreasing saprobic index and an increasing BMWP. Conclusions While temperature increased by + 0.9 °C during the past 30 years (1985–2014), our 15-year study period (2000–2014) showed a decrease by − 0.18 °C. Therefore, we regard the concomitant improvement in several assessment metrics as a recovery from prior increasing temperatures. In turn, we assume that increases in water temperature will lead to opposite effects and therefore cause declining assessment results. Water managers should be aware of this linkage that in turn could provide a chance to mitigate the effects of global warming by, for example, planting trees along the rivers and the removal of artificial barriers to increase current velocity to minimize a warming effect.