Restoring Entrenched Rivers: lessons learned from the

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1 Restoring Entrenched Rivers: lessons learned from the N i PProject j Napa Ri River RRestoration Andy Collison Geomorphologist ESA PWA acollison@esassoc.com

2 Napa County Flood Control and Water Conservation District Napa County Public Works Department The growers and landowners of the Rutherford and Yountville Districts The Rutherford Dust Society Napa County Resource Conservation District California Land Stewardship Institute California State Water Resources Control Board San Francisco Regional Water Resources Conservation Board California Coastal Conservancy California Department of Fish and Wildlife Environmental Protection Agency Our technical collaborators at Napa RCD, California DF&W, NMFS, Cramer Fish Sciences, Horizon H2O, SFEI, Tessera Sciences, A3GEO, Restoration Resources ESA PWA colleagues Ann Borgonovo, Jorgen Blomberg, Rocko Brown, Jason White, Aaron Fuller, Carlos Diaz, Barry Tanaka

3 Effects of entrenchment on ecosystem function Matt K, Laurel and Matt C Need to restore entrenched rivers Laurel and Matt C Causes of entrenchment on the Napa River Robin Introduce the Napa River as a typical example of channel incision and degradation in the Bay Area Challenges of restoring incised channels Discuss the idea of corridors and nodes as ways of organizing restoration efforts Design approaches for incised channels

4 Rutherford Reach 4 miles (Zinfandel Lane to Oakville) Yountville Reach - 9 miles (Oakville to Oak Knoll)

5 Initiated by Rutherford Dust Society and landowners in 2002 RDS initiated and funded the conceptual plan by Ellie Insley and PWA; landowners committed significant areas of riverside property at no cost, and significant capital investments to support the project Goals: Habitat restoration Erosion reduction & bank stabilization Regulatory context: Project was linked to the Napa River TMDL as a means of preemptively complying with RWQCB sediment reduction targets (TMDL was driven by Limiting Factors Analysis on salmonid decline)

6 Napa County (Public Works and Flood Control & Watershed Conservation District) has taken over leadership of project through detailed design and implementation Funded by: Napa County Measure A funds EPA Coastal Conservancy RWQCB CDF&W Landowners in kind contributions JSA and PWA developed % designs ~80% of project currently implemented

7 Initiated t dby landowners and California i Land dstewardship Institute in 2006 Conceptual Plan developed by CLSI, PWA and Napa County RCD, funded dby Napa County FC&WCD and SWRCB Napa Flood Control & Watershed Conservation District and CLSI are moving the project to detailed design ESA PWA team developed 30% design for 9 mile reach (Cramer Fish Sciences, A3GEO, RR) Horizon conducting CEQA process

8 Symptom Proximate Cause Intermediate Cause Sl Salmonid population decline Bank erosion Riparian forest decline Erosion of bed habitat forms Loss of floodplain habitat and connectivity Burial of spawning gravel by failed bank material Undercutting of banks Lowering of water table In ncision

9 Symptom Proximate Cause Intermediate Cause Sl Salmonid population decline Bank erosion Riparian forest decline Erosion of bed habitat forms Loss of floodplain habitat and connectivity Burial of spawning gravel by failed bank material Undercutting of banks Lowering of water table In ncision

10 Stage 1. Undisturbed dchannel l( (Pre 1900s) Aggrading regime, laterally unstable, riffles and pools, multiple habitats Classification model based on Simon and Hupp (1986), after Schumm (1984)

11 Stage 2. Leveed and managed channel ( s) Erosive regime, laterally static, vertically unstable, glide dominated

12 Stage 3. Incising channel (1950s onwards) Erosive regime, laterally static, vertically unstable, long glides, little spawning or rearing habitat

13 Stage 4. Incising and widening channel (most of Napa River at present) Erosive regime, laterally widening, vertically unstable, glides, loss of trees and gravel burial from failing banks

14 Stage 5. Widening and aggrading channel (some reaches at present) Channel reworks excess bank material into new bed forms and new floodplain

15 Restoration aims to help the channel evolve more rapidly to a new stable tbl condition Stage 6. New equilibrium channel Riffles and pools, bar colonization, new floodplain

16 Entrenched rivers tend to be: Hd Hydrologically ll disconnected d from floodplain l (too little water on the floodplain l ecological impacts) Subject to flow concentration (too much water in the channel erosion, degradation of aquatic habitat) Obvious solutions? Try to build cover and shelter into the entrenched river system? ( putting stuff in rivers approach) Doesn t deal with the underlying problems of entrenchment high velocity, excess erosive energy, lack of floodplain

17 Entrenched rivers tend to be: Hd Hydrologically ll disconnected d from floodplain l (too little water on the floodplain l ecological impacts) Subject to flow concentration (too much water in the channel erosion, degradation of aquatic habitat) Obvious solutions Reverse incision and bring channel back to floodplain Lower a new floodplain down to the channel bankfull elevation

18 Reversing Incision Fully restores floodplain inundation (good for ecosystem, bad for residents, infrastructure, many farming practices) How do you prevent re incision? Grade control needed unless all entrenchment stressors removed. Impacts aquatic environment (e.g. fairy shrimp, salmonids) Regulatory challenge fill Water of United States Lowering a new floodplain Maintains / improves existing flood protection level Only restores small areaof floodplain Only partially reduces confinement and erosion Impacts existing riparian corridor Very expensive to remove volume of sediment needed ($6M per mile for floodplain shown below excl. reveg)

19 How wide and how deep do inset floodplains need to be in order to provide worthwhile hil function? For any given volume (cost) what s ht the best trade off between length, width and depth of inset floodplains?

20 Rehabilitation corridor approach Existing, narrow riparian i corridor Restoration node approach Make a few areas highly functional and complex. Widen the corridor, setback levees, passive restoration, stabilize and replant the banks etc.

21 Depth/elevation link to geomorphology, fish life stage needs, inundation period and flow frequency Floodplain width link to erosion and energy dissipation Restoration node length optimize for sweet spot on width and depth curves? Node v corridor issues Floodplain node shape link to hydraulics, riffle pool maintenance

22 Traditional approach cut floodplains to just above bankfull elevation (~ year flow)

23 Napa River approach vary floodplains around lower elevations to compensate for loss of area

24 Many different biological criteria for floodplain inundation Refugia low velocity zones to shelter from high flows Feeding lanes need a sharp discontinuity between fast and slow flow to concentrate food Floodplain nutrient flush need a day or so to wash floodplain invertebrates into water column Floodplain activation flow need 2 3 weeks of inundation to build up a phyto and zooplankton web All these potential floodplain elevations need to lie within range of appropriate geomorphic elevations to be sustainable (i.e. not induce excessive deposition or other unwanted processes)

25 Primarily based on biological goals: Fish life stage requirements, inundation period and flow frequency Bench 3 ft above thalweg Chinook migration & spawning Chinook rearing Steelhead migration & spawning Steelhead rearing

26 Biological criteria for floodplain inundation Napa restoration projects Refugia low velocity zones to shelter from high flows Feeding lanes need a sharp discontinuity between fast and slow flow Floodplain nutrient flush need a day or so to wash floodplain invertebrates into water column Floodplain activation flow need 2 3 weeks of inundation to build up a phyto and zooplankton web may not have been a feature of Coast Range rivers, very challenging to restore on the current river

27 D 50 (mm) Shields Stress Channel Transport Type Values (T*) Height (ft) Height (ft) Slope Partial Transport Incipient Motion Selective Transport

28 Phase 1 Subsequent Phases

29 1.5 yr flow 3,843 cfs 2 yr flow = 5,790 cfs Activation Flows (cfs) # of Benches Length (ft) , , , ,000 Average % Time Activated* February March April 50% ~50% 20% 33% ~30% <10% ~25% 20% <10% 20% <10% <10% 10% <10% <10% <10% <10% <10% Total 29 8,500 *Based on 1- day flow exceedance for St. Helena Gage

30 Width somewhat correlates with geomorphic and biological function Deposition of bedload Spawning gravel Bed forms (riffles, bars, pool tails) Hbi Habitat complexity Growth of in channel vegetation Linked to fish abundance (e.g. Dunham et al 2002)

31 1% 2% 15% 42% 39%

32 Floodplain width = 0 Channel width How wide does an inset floodplain bench need to be, to significantly reduce erosive energy and velocity in the channel? Erosive stress at high flow Floodplain width / channel width

33 Floodplain width Channel width How wide does an inset floodplain bench need to be, to significantly reduce erosive energy and velocity in the channel? Erosive stress at high flow Floodplain width / channel width

34 Floodplain width Channel width How wide does an inset floodplain bench need to be, to significantly reduce erosive energy and velocity in the channel? Erosive stress at high flow Floodplain width / channel width

35 (ft/sec) y at Ten Year Flow Velocit Effects of Increasing Inset Floodplain Width on Erosion and Velocity Velocity Erosive Stress Incised, no inset floodplain Inset floodplain 12 x channel widths Floodplain width/channel width (lb/sq ft) Year Flow Erosive Str ress at Ten

36 Riffle or bar Pool

37 Riffle or bar Pool

38 Floodplain width at least 5 x bankfull channel width (Note that 80% of the Napa River Oakville reach is currently narrower than this) Floodplain elevations set significantly below Q1.5 with variation to suite fish life stage needs (but need to monitor low benches for excessive sedimentation) Originally thought length needed to be at least 1000 ft to allow bar development (from field observations); now finding bars forming on floodplain benches of a few hundred feet. Need to monitor short floodplain benches for longevity. Variable width to create secondary flow currents (expansion and contraction, leading to scour and deposition, promote velocity reversals) Shear stress level should deposit spawning gravel and erode finer material during most winter flows (e.g. Q2 shear stress = critical shear stress for 3 cobble?) Riparian buffer beyond floodplain to allow bank erosion/migration Secondary channels (mimics nature and allows existing riparian corridor to remain)

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48 Over the last decade we have developed much more scientific basis for designing inset floodplain benches Elevations linked to fish life stages Widths linked to hydraulics Shape and dimensions linked to riffle pool maintenance Challenges Optimum floodplain benches are large requires willing land owners Need to get away from idea of doing skinny but equitable restoration corridors towards restoration nodes Need to review long term sustainability of these features for geomorphic response and fish utilization

49 Entrenched reach (downstream of Yountville Bridge) Restored floodplain (Rutherford reach)