Nooksack Floodplain Integrated Management Planning
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Whatcom County Public Works River and Flood Division is leading a multi-year update to the old Lower Nooksack River Comprehensive Flood Hazard Management Plan completed in 1999. A Floodplain Integrated Management Planning (FLIP) process is underway with assessments in multiple disciplines being prepared to provide the technical information and interpretations needed. With the FLIP stakeholder-based integrated flood management planning process in mind, the following goals, objectives, and outcomes below were identified for this project. The FLIP process began as a System Wide Improvement Framework (SWIF) to evaluate PL 84-99 levee systems.
- ESRP has funded planning work in support of restoration project development
- NOAA provided funding for geomorphic analysis through a cooperative agreement with TNC in FFY 2016-18.
- The following findings were reported with completion of the geomorphic study:
- The lower Nooksack River system has been influenced by anthropogenic modifications and management over the past 150+ years. General Land Office (GLO) surveys from the 1880’s provide our earliest historic perspective on river form and function, recognizing that some modification had already occurred by the time of the surveys. Provided this historic context, the following is a summary of conclusions resulting from this assessment:
- The reaches from Deming to Everson were historically anabranching with forested islands dividing multiple channels. This river planform then transitioned to a single thread channel near Everson and remained single thread until the river hit Bellingham and Lummi Bays where multiple delta distributaries were evident.
- The Nooksack flowed north through what is now the Sumas River to the Fraser River in British Columbia as recently as 800 or 1000 years ago (the precise date is not determined) when an avulsion occurred and sent flow westerly to Bellingham/Lummi Bays. This history plays in important role in the current sediment/flow dynamics in the transition zone near Everson and on-going right bank overflows to Sumas and to Canada.
- Since the first maps of the river and especially since the 1933 aerial photos, the channel has been shortened and straightened.
- This has increased slope making it steeper and with more energy to move sediment and erode riverbanks and bed.
- This has caused the channel to be less connected to the floodplain providing less opportunity to store sediment and form habitat rich side channels.
- Narrowing of the meander belt width has produced a smaller wetted channel area and is associated with a conversion from a forested island type planform to largely single thread planform in upper Reach 3 and Reach 4 (Deming to below Everson).
- There is more woody vegetation now than in the recent past, but the wood is not of the size and quantity to form and maintain historic channel planforms and functioning habitat.
- There is now a higher energy channel that flows through a narrower, less complex corridor than was historically present; this relates in part to the historic extension of the levee and bank armor network.
- River regime theory, an examination of streambed sediment sizes, bank materials, hydraulics and other parameters, indicate Reaches 1 – 3 trend to be relatively narrow single thread channels while upper Reach 3 and Reach 4 are single thread but should trend towards anabranching (multiple thread) channels. Field observations and data collection corroborates the regime analysis.
- Finally, the USGS has provided data from their sedimentation study that indicates there are likely climate driven, miles long “waves” of sediment moving through the river. These waves may take 45 years to translate from near Glacier in the North Fork to Ferndale. The USGS work is summarized in the final report and will inform management options a key locations such as the Everson overflow where local aggradation may be related to such a wave with aggradation at the overflow site an incision in upstream areas the wave has passed through.