Rethinking river restoration: An integrated systems modeling approach to improve watershed habitat

Rivers and their riparian areas perform key ecological functions (e.g. food, shade, etc.) that contribute to sustaining ecosystem health. These functions are highly sensitive to human impacts. Most restoration projects target a specific area within the watershed and try to return that area to natural or near-natural conditions. In practice, projects use habitat quality indicators (e.g., Habitat Suitability Index) to monitor restoration of one or a few habitat attributes (e.g. instream flow, bank stability, flood regime). Rethinking river restoration requires a more integrated approach to represent all watershed habitat components. Systems models provide decision makers with tools to quantify and understand interconnections between different habitat components. They help predict and account for potential changes in the hydrologic, ecological, and management variables in water systems. Thus, planning and monitoring river restoration can be more effective with system models. However, applying system models in restoration practice require new and robust habitat quality indicators that are capable of capturing dynamic hydrologic and ecological changes in the watershed system with minimal data-collection effort. We have developed a Watershed Habitat Performance (WHP) indicator (measured in unit area) that quantifies habitat performance in four areas; aquatic life, riparian area, floodplain and diked wetlands. The WHP sums four sub-indicators. An aquatic life sub-indicator measures the habitat suitability for aquatic species as a function of water depth, and channel surface area. A riparian area sub-indicator measures the protection of riparian land as a function of the length of protected river shoreline. A floodplain area sub-indicator measures the suitability of the floodplain to support native vegetation as a function of flood frequency, flow, floodplain area and vegetation nativity. Finally, diked wetland sub-indicator measures the suitability of wetland units to support priority bird species as a function of water depth, invasive vegetation control and wetlands unit area. The model maximizes the sum the four sub-indicators with different weights that vary spatially and temporally. The systems model attempts to maximize watershed habitat performance by adjusting the decision variables that contribute to the values of the four sub-indicators. These variables include water depth, flow, invasive vegetation control and river bank protection). These variables are incorporated into the systems model that recommends allocating scarce water to maximize the WHP. The optimization is subject to certain restrictions and management limitations (e.g. water rights, storage and infrastructure capacity, budget). We validated this conceptual model using data on the Lower Bear River, Utah that were collected through the Bear River Fellows Program. Our findings will be discussed with the River managers to help recommend alternatives to better allocate water to improve environmental watershed services and secure water for wetlands and riparian areas.