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Stream restoration is an interdisciplinary science that requires input from natural science, social science and engineering experts. Our team approach is to cross departmental lines to represent viewpoints of fluvial geomorphologists, engineers, hydrologists, aquatic biologists, natural resource specialists, operators, planners, educators and community relations experts. We believe the sum of the team is greater than the individual disciplines by themselves. Our approach is to develop in-house staff expertise in all phases of the work, including assessment, design, permitting, construction and monitoring. We believe our multi-discipline, diversified team approach will result in selecting appropriate project sites, providing efficient designs and implementing self-sustaining projects.
While many methods of stream restoration exist, the San Antonio River Authority's (River Authority) stream restoration projects will focus on a particular restoration technique known as Natural Channel Design (NCD). The NCD approach relies on the principles of fluvial geomorphology to evaluate the current state of the degraded stream and that stream's potential for restoring its historic functions. The fluvial geomorphology of a particular stream can include the interactions of climate, geology, topography, vegetation and land use in its watershed.
The end result of the NCD method develops a functional, self-sustaining stream system that provides valuable hydraulic (water transport), geomorphic (sediment erosion and transport) and ecological functions. By improving hydraulic and geomorphic functions, NCD creates a stable stream channel that can move water and sediment generated by its watershed while maintaining channel structural characteristics (such as dimension, pattern and profile) so that over time, the channel does not fill with sediment or erode continually downward.
The NCD approach uses more natural reference streams to compare the degraded stream functions with a functioning stream, provide a "blue print" for the stream restoration design and establish performance standards during post construction monitoring. In addition, establishing and maintaining good communication with the project stakeholders and using technical judgment on what is practical for each project site is a critical element to a technically successful and cost effective project. Further detail can be found in the Rosgen Stream Classification Technique section of the Natural Resource Conservation Service (NRCS) Engineering Manual.
As a part of NCD stream restoration projects, the relationship between the stream and its floodplain is returned to a condition that maximizes stream function. In a natural stream system, a stream will overflow its channel on average every 1.5 years, which allows pollutants to be processed on the floodplain, wetland-adapted plants to flourish in these areas and most stream functions of value to humans to be performed. However, the relationship between the stream channel and its floodplain can change under two main scenarios: stream degradation and intentional human alteration.
In a degraded stream system, channels can erode downward so deeply that it is no longer possible for water to come out of the channel during anything but an extremely large flood event, and few stream functions can occur. There are many methods of stream restoration available using NCD techniques to correct this problem, depending on the availability of space adjacent to the channel for increased water on the floodplain without damaging nearby infrastructure.
In a degraded stream system, channels can erode downward so deeply that it is no longer possible for water to come out of the channel during anything but an extremely large flood event, and few stream functions can occur. There are many methods of stream restoration available using NCD techniques to correct this problem, depending on the availability of space adjacent to the channel for increased water on the floodplain without damaging nearby infrastructure.
A more challenging situation is when streams are separated from their floodplains as a result of channelization projects that are used to protect infrastructure next to the stream. During channelization, the stream channel and its associated flood control channel (shown in red) is lowered below the original floodplain so much that only an extremely large flood event will bring waters in contact with its original floodplain. Channelization is an effective flood control method, but does little to allow the stream to function in a natural way and provide other benefits. To address this loss of function, an NCD Three-Stage Channel can be constructed within the flood control channel. This essentially allows a floodplain to be constructed within the flood control channel that is lower than the original floodplain. This allows for a more stable stream that performs more of the functions of a natural stream, without endangering the nearby infrastructure.