Creation of a geospatial tool to locate optimal reference reach sites for natural channel design restoration methods
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2019-07
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MAHER, CLARE. Master of Natural Resources, Hydrology. Creation of a Geospatial Tool to Locate Optimal Reference Reach Sites for Natural Channel Design Restoration Methods.
In fluvial geomorphology, natural channel design techniques are often used for stream restoration in order to create stable channels and increase stream functions as much as possible. Establishing design criteria for a restoration project is one of the most critical components of a successful natural channel design. The most common method of establishing numerical criteria for channel design characteristics such as dimension, pattern and profile is through a reference reach survey. A reference reach is a stable channel segment that serves as a model for restoration, and is described by quantitative field data of its morphological features. Analyzing the suitability of a new reference reach site requires an extensive field survey to determine critical morphological metrics. Therefore, finding new reference reach sites is time consuming and often impractical. Additionally, it can be difficult to find new reference reaches due to widespread growth of urban, suburban and agricultural land use in the United States. Stream restoration designers often use the same reference reach sites for several projects due to data availability. Although many reference reaches can serve as valid stream design models for multiple projects, they might not be the best fit when considering all morphological characteristics of the stream. When working with a small selection of reference reach sites, it is more likely that multiple sites will need to be used in the design process to achieve the optimal ecological function. Given access to a wider selection of reference reach sites could yield higher quality restoration designs and streamline the design process. Ultimately, to adequately select a reference reach site for a degraded stream channel, ecological restoration designers must be knowledgeable of its fluvial geomorphology, which includes its natural function and interactions with the surrounding landscape.
The function and landscape interactions of streams are constantly changing, but an understanding of these morphological characteristics can aid in determining stream stability and response to stressors. Stressors that can reduce the stability of a stream system include climate change, land use/land cover change, and artificial hydrologic structures. These stressors all affect the streamflow and/or sediment load of a stream in some way, which ultimately changes its morphology. For example, urban development can decrease the floodplain width and cause channelization of a stream. The absence of a wide floodplain increases the amount and velocity of water flowing through a stream, which erodes the banks and alters the physical shape of the channel. Loss of stability in a stream system not only alters the physical characteristics, but also affects the overall ecological health of a stream. When morphological changes occur, a loss of biological diversity within the stream ecosystem can also occur due to habitat alteration or loss. Knowledge of the fluvial geomorphology and surrounding land use of a stream channel helps restoration professionals to predict its response to stressors and create a design plan that reflects that.
In natural channel design, the reference reach is a critical component of a restoration project’s design plan. Restoration projects are often contracted from state agencies to private mitigation companies. Therefore, mitigation reports and related project data are made publically available. Although not required, reference reach locations and their morphological data are usually included within mitigation reports. A reference reach database was created using publically available data from the North Carolina Department of Mitigation Services (DMS). This database is used as the foundation for the Reference Reach Finder Tool (RRFT). The purpose of this project is to make the identification of reference reaches easier by creating a Geographic Information Systems (GIS)- based tool. We believe that this RRFT will improve the stream restoration design process and have important benefits to natural ecosystems.
