Streaming Media
Presentation Abstract
Projected changes in coastal sediment dynamics and flood exposure in the coming decades have important implications for estuary ecosystem recovery strategies and principal barriers to their implementation, namely transportation and flood control infrastructure. A numerical sediment transport model was used to evaluate whether the flux of sediment from the Nisqually River to the 308-hectare 2009 Brown’s Farm restoration project is sufficient to recover 1–2 m of subsided marshes given projected sea level rise. The effectiveness of distributary channel restoration alternatives in rerouting and introducing Nisqually River sediment to the restoration area were also assessed. Model and measurements indicate that ~10% of the fluvial sediment load reaches the delta; most is trapped in Alder Lake reservoir 65 km upstream. Modeled scenarios show that of the fluvial sediment load reaching the delta 7–32% accumulates in the restoration area under existing conditions and that an additional 10–12% could be gained with distributary alternatives. The limited potential for recovering sediment results from the sediment pathways located low in the tide range and the influence of waves on offshore export. Predicted accumulation rates suggest that 85–200+ years are required to recover the marshes and that restoring sediment supply upstream where transport is restricted by the Interstate-5 infrastructure and/or external nourishment may aid recovery. A second compound flood model evaluated the vulnerability of the I-5 and neighboring infrastructure to potential flooding expected with higher sea level and peak stream discharge in the coming decades. Modeled extreme water levels of 10-yr and 25-yr recurrence floods by the 2040s and 2080s and flow restriction from the I-5 causeway result in overtopping of I-5 and surrounding roadways. Together, the sediment and flood modeling provide insights to constraints on ecosystem recovery and opportunities for coordinated investments to expedite recovery goals and enhance community resilience.
Session Title
Data Science 3
Conference Track
SSE1: Science for the Future
Conference Name
Salish Sea Ecosystem Conference (2022 : Online)
Document Type
Event
SSEC Identifier
SSE-traditionals-225
Start Date
28-4-2022 10:15 AM
End Date
28-4-2022 11:45 AM
Rights
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Type
Text
Language
English
Assessment of vulnerabilities and trade-offs for coordinated investment in regional ecosystem recovery and flood resilience, Nisqually Delta, Washington State, USA
Projected changes in coastal sediment dynamics and flood exposure in the coming decades have important implications for estuary ecosystem recovery strategies and principal barriers to their implementation, namely transportation and flood control infrastructure. A numerical sediment transport model was used to evaluate whether the flux of sediment from the Nisqually River to the 308-hectare 2009 Brown’s Farm restoration project is sufficient to recover 1–2 m of subsided marshes given projected sea level rise. The effectiveness of distributary channel restoration alternatives in rerouting and introducing Nisqually River sediment to the restoration area were also assessed. Model and measurements indicate that ~10% of the fluvial sediment load reaches the delta; most is trapped in Alder Lake reservoir 65 km upstream. Modeled scenarios show that of the fluvial sediment load reaching the delta 7–32% accumulates in the restoration area under existing conditions and that an additional 10–12% could be gained with distributary alternatives. The limited potential for recovering sediment results from the sediment pathways located low in the tide range and the influence of waves on offshore export. Predicted accumulation rates suggest that 85–200+ years are required to recover the marshes and that restoring sediment supply upstream where transport is restricted by the Interstate-5 infrastructure and/or external nourishment may aid recovery. A second compound flood model evaluated the vulnerability of the I-5 and neighboring infrastructure to potential flooding expected with higher sea level and peak stream discharge in the coming decades. Modeled extreme water levels of 10-yr and 25-yr recurrence floods by the 2040s and 2080s and flow restriction from the I-5 causeway result in overtopping of I-5 and surrounding roadways. Together, the sediment and flood modeling provide insights to constraints on ecosystem recovery and opportunities for coordinated investments to expedite recovery goals and enhance community resilience.
