Tidal Wetland Project
Parsons Slough Project Restoration Plan
Meeting Notes
12-2-08 1-4pm
JOINT: Strategic Planning Team, Science Advisory Panel, and Parsons Advisory Committee
Attendees: Jeff Cann,Aaron Carlisle,Peggy Casper, Allison Chan,Trish Chapman, Ross Clark,Noel Davis, Mike Eng,Ed Gross,John Haskins, Kim Hayes,Brent Hughes, Linda Jordan,John Krause,Bryan Largay, Steve Legnard, Steve Lonhart, Suzanne Marr, Jacob Martin, Erin McCarthy, Shirley Murphy,Jim Oakden, Mark Silberstein,Dilip Trivedi, Christina Toms, Eric Van Dyke, Kerstin Wasson, Chris Webb, Andrea Woolfolk (note: sign-in sheet was not completed by all participants)
Notes taken by: Kerstin Wasson
Introduction and Parsons Slough Restoration Planning Process (Bryan Largay, ESNERR)
- Review of marsh loss, attributed to sediment deficit relative to tidal inundation, and review of bathymetric changes (deepening and widening channels & creeks)
- Review of TWP goals and planning principles
- Review of large scale strategies
- Review of Parson’s historical ecology: dense salt marsh in earliest records, then freshwater impoundments to east and in cloverleaf pond to north; after harbor mouth opens, remaining dense salt marsh thins; then additional diking; in 1983, return of tidal exchange to subsided, formerly diked complex leading to lagoons and mudflats
- Review of Parsons Restoration Planning Process and Team
Parsons Slough Restoration Plan (Chris Webb, Moffat & Nichol)
Main goal was to try to examine strategies for significantly increasing extent of salt marsh in Parsons complex, either by controlling water levels or by raising elevation
0. No action
Basis for comparison; maintains existing conditions and likely to lead to trajectory of increased deepening (existing marshes and mudflats convert to subtidal); considered unacceptable for project goals [project goals are attached].
1. Water control structure at UPRRBridge
Control tides with weir structure and pipes to halt channel scour; allow salt marsh to colonize areas that are currently mudflat; assist with partial earthen dikes constricting channels into Five Fingers; water quality of concern because residence time may increase to 2 weeks in some areas; pipes also are barriers to fish and marine mammals; habitat diversity declines in muted system; maintenance and management especially in the face of sea level rise is challenging.
2. Sill downstream of UPRR bridge and add sediment
Retain sediment and halt channel scour; mostly add sediment, but use sill to aid in sediment retention; sill at about -2 ft below MLLW, earthen core with rock armor surface; do incremental sediment additions at sixth finger, Rookery, etc.; to raise whole area to elevation for salt marsh; would take an enormous amount of sediment and presumably many years to implement; water quality is maintained similar to existing conditions; fish and marine mammal passage not problematic; habitat diversity broad; sill would require little to no maintenance; can manage adaptively in the face of sea level rise by raising sill and adding sediment.
3: Internal muting, diking and adding sediment
Control the tide just within fingers with water control structures to retain sediment and increase marsh colonization because elevation would be higher relative to tides; less sediment needed than in Alternative 2 because of this; water quality would be impaired if muted significantly; water control structures would pose barriers to fish and some marine mammals; habitat diversity would decline; requires maintenance and will not function well in the face of sea level rise.
Narrowing of alternatives
The Parsons Slough Team, a technical advisory group, Eliminated Alternative 1 and the muting scenarios of Alternative 3.
Two options retained: Alternative 2 (sill and sediment addition) and Alternative 3 without muting (partial constrictions of various components with sediment addition).
Desired topography for all except channels is to about 5 ft above MLLW.
Discussion
Clark: what is effect of Alt 2 on decrease of tidal prism in Slough as whole?
Webb: substantial if elevation is raised everywhere; minimal if only in one Finger
Jordan: what is role of UPRR in these decisions that affect water level around RR berm
Webb: unclear at this point; desirable would be to raise RR bed as a part of Parsons restoration project
Silberstein: North Azevedo Pond project may be small scale example of how we can do restoration in collaboration with RR; after earthquake, railbed sank >1 ft, and the next day the RR was out raising it again, so our assumption is that it will be continually raised in the face of sea level rise
Van Dyke: maintenance supervisor from Watsonville said there is no guidance from above yet on sea level rise strategies
Sill effect on tidal exchange
Two sill options were considered, one the full width of the channel and one half the width of the channel. Both options reduce velocities in the main channel of Elkhorn Slough downstream of the Parsons Confluence, with a more pronounced effect with a narrow sill.
1 ft/sec velocity erodes fine sands; 3 ft per second erodes coarse sand and silts/clays
With sill in place, velocities in lower Elkhorn main channel drop from above 3 to below 3: should slow Elkhorn; 20% reduction in peak velocity downstream from Parsons entrance; but 8% increase upstream of Parsons entrance (slight hydraulic gradient that draws water down from upper Slough as a result of sill)
Largay: this is consistent with independent PWA projections of increased velocities/scour off of HummingbirdIsland
Gross: can you design a sill structure to decrease the effects of high tides, narrow shape?
Trivedi: not easy to do, end up with very high velocities or use water control structure to mute tides – the narrower you make it the more it is like the muting structure considered and rejected earlier
Wasson: tidal velocities within Parsons are not high enough to lead to erosion; isn’t that inconsistent with projections of increased deepening under no action scenario
Webb: yes, but we didn’t pick the most erosive sites for the model output.
Slurry line concept
Examined various options for sediment import: trucking, rail, pipe from harbor or ocean, low profile barges. Most promising appeared to be slurry line from quarry (Graniterock).
Graniterock dust byproduct: silt sized particles, inert, no organic content, >50% silica.
Could be obtained cheaply or at no cost, except for transport.
They used to dump it into SodaLake.
Could slurry it to Elkhorn, but would need consistent source of water; could pipe water up from Slough, or find freshwater source up there.
About 300 ft uphill from Elkhorn, so gradient works, with booster pumps.
Water side slurry distribution lines would be run along RR (need right of way) and distributed in network to fingers. Could also be run around from land side.
Cann: would you need to cap the granite sediment with other organic sediment
Webb: yes, granite would be suitable base material which could then be capped with more suitable sediment, such as perhaps from one of the harbor dredging operations
Toms: would need to find appropriate organic source such as horse manure
Largay: colonization by invertebrates and vegetation may proceed and enrich it with organics without any additional assistance
Cost
Alt 2 restores much more marsh, at much greater cost ($50 M)
Alt 3 restores much less marsh, at much lower total cost ($28 M) but more per acre for some parts
Habitat changes
Between 1913 and 2000, have seen 70% increase of mudflat, 40% decrease in salt marsh
Currently, 4% of area is salt marsh, 81% is mudflat.
What should we aim for? Maybe 50:50?
Van Dyke: economy of scale question – is there a threshold for getting best economic efficiency? shouldn’t do too small a project because it would be relatively expensive
Trivedi: need million yards for either alternative to get the cost that was estimated
Davis: might want to try pilot with trucked material in 6th finger before building pipeline
Wasson: seems like there are 4 options, sill yes/no and fill incremental/total; why are we only discussing 2 options (sill with total, no sill with incremental)?
Webb: can’t do total fill without sill (would lose material from the middle channels without a sill to retain it); but there are basically 3 options: sill with total fill, sill with incremental, and no sill with incremental
Lonhart: what is fate of sediment after initial pumping in; does it move around a lot
Trivedi: have to control sediment movement, by rapid marsh colonization facilitated by topsoil and/or notching channels to get channels where you want them
Toms: could maybe do some sort of prevegetation treatment to keep material in place when you open it to full tidal exchange – sacrificial plant community.
Oakden: is 120K/restoration acre acceptable?
Chapman: it is within range that they see, but high
Davis: Bolsa Chica was 150K/acre
Clark: chose Parsons as a pilot because it was of a scale where it could affect the whole system and yet still be an experiment; but tidal prism reduction is not as great as hoped and cost is much higher; maybe we should turn around and look to see whether there are other things we could do in rest of system for same funding, greater benefit; could redirect some of this potential funding, 50 million or so, to the mouth of Elkhorn Slough
Largay: we could examine sill that has more benefits for tidal prism reduction, but will have higher velocities and higher turbulence
Chapman: basic assumption of goal of Parsons that benefits whole system seems violated by PWA and M&N predictions of greater scour upstream
Gross: you reach the same endpoint either way (even in no action the velocity increases upstream of Parsons, it just takes longer to get there); it is a transient phenomenon
Toms: going faster because the water that used to be in the way isn’t there anymore
Largay: net reduction of tidal scour with Parsons, disproportionately focused on lower Slough
Lonhart: but what we need to know is 50 or 100 year endpoint and how it differs under different options; is action in Parsons Slough leading to net change in main channel in long term?
Chapman: another thought to consider is what we would do if there is only 5 million, not 50 million dollars to spend
Silberstein: there may be some incremental benefits to small scale projects at Parsons; PWA modeling showed that sill at mouth didn’t really buy us any salt marsh in the long term, in the face of sea level rise. So small salt marsh restoration projects might be a better investment; one logical one for starters is testing Graniterock material.
Largay: integral to the sea level rise projections of PWA was the assumption that our marsh plain is not accreting, but this appears to be violated by sediment accretion studies by Van Dyke, Watson, Woolfolk; also, they assumed there was no sufficient sediment source, but we may be able to find one
Trivedi: we may be able to arrest scour but none of these solutions are sustainable in the face of sea level rise; only muting really does that, but at cost to quality
Habitat types and impacts to existing habitat (Group Discussion)
Largay: to target areas within Parsons for sediment addition, want to pick areas with current low quality not high quality;
Van Dyke: aesthetics are an important consideration in a public access area, by this criterion South Marsh is a great choice because of the ugly marina-like design of the islands; another consideration is natural features: would be concerned about potentially damaging the natural sinuous channels of the fingers, but no such concerns with the artificial structure of the islands; also seems like the linear arms would be useful as partial dikes for holding in sediment
Largay: yes, areas of intensive soil disturbance would be good targets in general
Murphy: from a tour guide standpoint, doesn’t want to see everything converted to pickleweed because visitors like to see shorebirds
Quick poll: Nobody supports close to 100% marsh in Parsons; a few are in favor of 75%; no vote taken on 50%, as the group appeared reluctant to commit to those targets at this time
Chapman: need to make it clear in report that freshwater was artificial here; M&N report makes it sound like baseline
Wasson: to determine what % of marsh we want at Parsons need to know whether it will be our sole salt marsh preserve for posterity, where we will fight sea level rise, undo subsidence, etc.; if so, want high %, but if Porter or Moro Cojo or other sites are those preserves, could have much lower percentage
Oakden: habitat value of Parsons and Five Fingers is low; some portions near the entrance are armored, so shouldn’t talk about mudflat values
Largay: are people comfortable with 6th finger as option?
Van Dyke: not as first place, better to do experiments in artificial area like South Marsh
Toms: often need to excavate sinuous channels because they won’t form that way naturally (often straight in restoration projects)
Lonhart: we seem to always take one step forward, two steps back in this process; but given the sticker shock, what other options do we have on other places with better bang for buck? it is such an expensive pilot and may not give us what we want.
Largay: to get combination of reducing tidal prism and restoring salt marshes, there aren’t a lot of other options; could restore marshes along main channel but would not be any cheaper
Clark: we are talking here about restoring salt marsh while we have salt marsh currently along main channel that we are losing; maybe it would make sense to add sediment to those areas, conservation of high quality instead of restoration of degraded areas; interesting to at least address experimentally
Silberstein: Moro Cojo has 1000 acres of former wetlands, Porter Marsh has lots, etc. but Parsons was the one place where by simply pinching off the flow we could potentially make a big difference on the system
Chapman: two very distinct sediment paths, a small amount to an area that hasn’t lost its marsh vs. a large amount to a very subsided area; can approach both at once in different ways, small addition experiments in main channel, experiments with granite dust in Parsons
Largay: We would like guidance on which experiments to conduct:
--bucket experiments for invertebrate colonization
--mesocosm experiment to look at invertebrate colonization and marsh colonization
--pilot experiment – a few acres
Wasson: larger scale, longer term is most informative for understanding important outcomes; wouldn’t really care if invertebrate community were altered for a few months or years so long as it recovered over multiple years: we are in this for the long term
Lonhart: pilot scale is best for shedding light on likely outcome of real project too; hard to scale up from buckets or mesocosms
Jordan: rookery lagoon seems good site for pilot, because so calm
Oakden: buckets are handy for trying different mixes of sediments; also want to assess what types of larvae are out there so you understand which natives vs. non-natives like different sediment types; buckets are also useful for reducing variation and getting clearer signal
Wasson: invertebrate recruitment seems fairly tangential if you are a going to do sediment addition to 5 ft above MLLW right away; not many invertebrates present at that tidal height; of course some would spill into channels, so invertebrates are of secondary interest
Chapman: no harm in doing buckets while you are working on permits for pilot, and makes permitting more viable to have some information on how pure granite functions vs. adding some capping from harbor sediments
Silberstein: 6th finger cheaper for sediment addition pilot due to access
Clark: wants to put in another plug for sediment addition experiments along main channel
Murphy: why not fill in Whistlestop Lagoon?
Largay: science will be expensive part of this planning
Silberstein:need prioritized list of restoration science experiments so we can then recruit folks for them
Additional agenda items tabled for later discussion
What impacts of the proposed sill are acceptable?
Sediment additions and sea level rise considerations
Habitat sustainability in an environment of rising sea levels