Restoring the Napa River:

Transcription

1 Restoring the Napa River: lessons learned from a long term private-public project Andy Collison Environmental Science Associates acollison@esassoc.com 1

2 Napa River Restoration Projects Rutherford Reach 4 miles Yountville Reach - 9 miles

3 Project Highlights A long term, large-scale project From 2002 to 2017 and beyond 13 miles of channel evaluated for geomorphic and ecological function The opportunity to experiment and learn from different restoration methods A successful private-public project 100% landowner participation in Rutherford project (32 landowners) Commendation from the California Legislature as an outstanding project Clients Rutherford Dust Society and the landowners of the Rutherford and Oakville reaches Napa County RCD & Napa County Watershed and Flood Management District Napa County Public Works Department Funding agencies and land donations: Napa County Measure A flood management bond EPA, State Water Resources Control Board, RWQCB, California Coastal Conservancy, California Dept. of Fish & Wildlife, landowners

4 Project Initiation and Evolution Initial project drivers Private landowner initiative (Rutherford appellation) Bank stabilization Flood management River restoration Pierce s Disease control (non native host plant removal) Regulatory drivers Napa 303d listed as impaired for chinook and steelhead spawning and rearing due to excessive erosion and sedimentation Required a 50% reduction in bank erosion RWQCB designated participation in the restoration plan as a form of TMDL compliance Landowners were able to get in front of regulations by participating

5 Project Initiation and Evolution Landowner organization/funding Owners formed an informal self assessment district and charged themselves based on the length of river frontage Subsequently formalized into a Mello Roos Community Facilities District Owners pay into stream maintenance program Subsequent phases Napa County RCD and subsequently Napa Flood Management took over funding and project management Landowner coordination Ellie Insley, Lisa Micheli, Gretchen Hayes, Laurel Marcus

6 Napa River Symptoms Versus Causes Symptoms Salmon decline Bank erosion Lack of riparian regeneration Causes Channel incision & widening

7 Napa River channel incision 8 feet in 40 years 2-4 feet in 40 years

8 Flow Concentration Photos courtesy of SFEI 1940 Flows spread out over many small channels limited erosion

9 Flow Concentration Photos courtesy of SFEI 2006 Higher flows concentrated into fewer channels increased erosion

10 Photos courtesy of SFEI 2006 Higher flows concentrated into fewer channels increased erosion

11 Napa River Evolution Stage 1. Undisturbed channel (Pre 1900s) Aggrading regime, laterally unstable, riffles and pools, multiple habitats Classification model based on Simon and Hupp (1986), after Schumm (1984)

12 Napa River Evolution Stage 2. Leveed and managed channel ( s) Erosive regime, laterally static, vertically unstable, glide dominated

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

14 Napa River Evolution 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

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

16 Stage 6. New equilibrium channel Riffles and pools, bar colonization, new floodplain

17 Stabilization can fossilize the channel in an unstable and ecologically undesirable condition Stage 6. New equilibrium channel Riffles and pools, bar colonization, new floodplain

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

19 Landowner outreach geomorphology 101 for growers Emphasis on reducing erosive stress by widening channel rather than increasing resistance by hardening the channel

20 The Half a Million Dollar an Acre Question: how wide does the river need to be, to restore function?

21 The Half a Million Dollar an Acre Question: how wide does the river need to be, to restore function? Width:depth ratios W:D = 4:1 Spawning gravel eroded during winter flows W:D = 6:1 (average for Napa River in project area W:D = 9:1 Start to see geomorphic complexity and sediment sorting W:D = 14:1 W:D = 21:1

22 Key design elements Channel widening to reduce erosive energy and allow gravel deposition Biotechnical bank stabilization Bank flattening to reduce erosion, create plantable surfaces Native planting In channel large wood structures to create salmonid habitat Reaches 1&2 advanced to final design by another firm and constructed

23 Lesson learned: avoid uniform floodplain bench height and width 1.5 year flood elevation

24 Lesson learned: avoid uniform floodplain bench height and width Large excavation volume and cost Fixed setback 1.5 year flood elevation 2008 PWA (now ESA) brought back in to refine design in light of lessons learned from implementing Reaches 1&2

25 Lesson learned: avoid uniform floodplain bench height and width Variable setback year flood elevation

26 Lesson learned: avoid uniform floodplain bench height and width

27 Lesson learned: lower elevation of designed floodplain benches over time to be more actively engaged by river and fish

28 Floodplain Benches July 2014 March 2016 December 2014 Images from Napa County Flood Control and Water Conservation District

29 Floodplain Benches March 2012 October 2011 March 2016 Images from Napa County Flood Control and Water Conservation District

30 Large Wood Structures

31 Lesson learned: Over time we have become more aggressive in our wood placement Large Wood Structures

32 Napa Rutherford Summary Statistics Design, permitting and implementation % landowner participation (32 landowners) Achieved 80% of the TMDL fine sediment reduction goal for the entire Napa River 70% reduction in length of eroding banks 2.5 mi of channel corridor widened 3.25 ac Arundo donax removed 147 in-stream habitat structures installed ~3,050ft of secondary channel created 12 ac high flow fish refugia created 21 ac riparian forest restored spawning gravels deposition widespread in restored reaches

33 Napa Oakville to Oak Knoll Restoration Similarities Landowner initiated Way to meet TMDL compliance Differences Fewer, larger landowners More corporate owners

34 If you can t fully restore an entire river corridor, what approach do you take? Rehabilitation corridor approach Existing, narrow riparian corridor Restoration node approach Make a few areas highly functional and complex. Pros: Very high value habitat areas Make the whole corridor somewhat more functional Cons: concentrated costs, concentrated risks Pros: - Equitable for landowners - Spreads habitat benefits and risks - Suited to migratory species? Cons: - Lots of good but not great habitat?

35 Tributaries as small restoration nodes: Bella Oaks Tributary acres -24,000 CY excavation -Channelized confluence SOURCE: GOOGLE EARTH

36 Bella Oaks-October 2013, under construction Note tree island at mouth of old channel SOURCE: GOOGLE EARTH

37 Bella Oaks-August 2014, first year after construction SOURCE: GOOGLE EARTH

38 Bella Oaks-March 2016, three years after construction Note tree island and gravel bar formation SOURCE: GOOGLE EARTH

39 Group C Project a large node restoration Site FT

40 Managed retreat A phased approach for managed natural channel widening Compatible with vineyard block replanting (e.g. replant vines every 20 years) Useful where active widening would removal all the existing riparian corridor Doesn t require permits or construction! (Can build into permits to allow eventual bank protection)

41 Napa Yountville Project Highlights Design ( ) Construction ( ) 9 Mile Project Reach 2.4 Miles of Restoration 66 Acres of Channel & Riparian Habitat Restoration ~420,000 Cubic Yards of Grading (Enough to Cover a Football Field ~200 Feet Thick!) 76 Acres of Revegetation & Vegetation Management >200 Instream Structures Installed 29 Acres of Vineyard Rededicated to River Corridor LWD Site 22 & 21

42 Napa River Lessons Learned For floodplain restoration, lower is better Traditional bankfull elevation floodplains are left dry during low flow conditions Lower than bankfull benches will potentially trap sediment or be inundated more frequently Can floodplains be too low? We are monitoring but so far non have filled in Floodplain bench length is significant Benches which are short (approx. 1-2 channel widths) will induce eddying and prevent sediment deposition Nodes and corridors in many cases nodes may offer more ecological bang for the buck Consider passive restoration e.g. managed retreat

43 Questions? Andy Collison