GIS Framework for Large River Geomorphic Classification to Aid in the Evaluation of Flow-Ecology Relationships

Abstract

Providing a means to quantitatively define flow-ecology relationships is integral in establishing flow regimes that are mutually beneficial to power production and ecological needs. This paper presents a geographic information system (GIS) framework for large river geomorphic classification that is flexible, accurate, and easily integrated with Ecological Limits of Hydrologic Alteration (ELOHA) initiatives. A case study was conducted integrating the base geomorphic aspect of this framework with the Modular Aquatic Simulation System two-dimensional (MASS2) hydraulic model and field collected data to establish optimal juvenile salmonid rearing habitat under varying flow regimes throughout an impounded portion of the lower Snake River, USA. Defining regions of optimal juvenile salmonid habitat at varying flows was used to distinguish areas that have a high potential for the creation of additional shallow water habitat. Findings indicated that the potential to create additional shallow water habitat does exist for juvenile salmonid rearing regardless of the flow scenario (discharge exceedence levels of 1, 25, 50, 75, and 99 percent) for the sample time frame (May -June 2011). The left-bank habitat of the lower Snake River was also found to be preferable for juvenile salmon rearing compared to right-bank habitat. The results from the case study suggest that the GIS framework is a capable tool when used to diagnose flow-ecology relationships. Additionally, an alternative hydrologic classification system is explored that couples well with the geographically independent nature of this GIS framework. Future applications of this framework are to utilize it in other large river systems throughout the contiguous United States. The framework also allows for the organization of large river data to be quickly accessed and used for multi-river comparison and analysis. Future development of a backend database within an interactive web platform would be highly beneficial to create a readily available and standardized mechanism to facilitate classification efforts conducted at the national scale.iv

A Holistic Framework for Environmental Flows Determination in Hydropower Contexts

“…Reach or habitat classifications become advantageous in stratifying locations for instream flow studies, assessing the presence/absence of species, and prioritizing areas for morphological restoration. For example, Vernon et al (2013) developed a geomorphic classification framework in conjunction with a two-dimensional hydraulic model to assess optimal juvenile salmonid rearing habitat under varying flow regimes in the lower Snake River Basin. Reachscale geomorphic classifications can increase the predictive accuracy of flow-habitat models and provide a template to assess alternative mitigation strategies.…”

“…Reachscale geomorphic classifications can increase the predictive accuracy of flow-habitat models and provide a template to assess alternative mitigation strategies. For example, the output from the geomorphic classification and two-dimensional hydraulic model (Vernon et al 2013) can be used to determine the feasibility of flow restoration compared to morphological restoration. Specifically, gravel addition may provide more ecological benefits than flow restoration.…”