6/6/05
Elkhorn Slough Tidal Wetland Plan
Elkhorn Slough National Estuarine Research Reserve
JOINT Science Panel and Strategic Planning Team
Meeting Summary
Meeting Date and Time: April 13, 2005, 9:30 a.m. – 3:30 p.m.
Meeting Location: Elkhorn Slough National Estuarine Research Reserve
Prepared by: Jan Shriner, Kerstin Wasson, and Barb Peichel
Attendees: Sean Anderson, Jeff Cann, Becky Christensen, Ross Clark, Bob Curry, Sarah
Fischer, Jim Harvey, Craig Jones, Rikk Kvitek, Jessie Lacy, Bryan Largay, Robert
Mazurek, Nick Nidzieko, John Oliver, Barb Peichel, Josh Sampey, Dave Schwartz, Jan
Shriner, Mark Silberstein, Peter Slattery, Eric Van Dyke, Kerstin Wasson
Purpose of Meeting:
Characterize the likely future trends for habitats (unrestricted tidal flow) in the Elkhorn
Slough watershed for a no action management alternative and discuss potential largescale alternatives to reverse undesirable trends.
Outcomes:
Identification of agreement on statements predicting likely trends for channel, mudflat,
and salt marsh/tidal creek habitats (unrestricted tidal flow); Understanding of substantive
disagreements with predictions of likely trends; Dialogue about justifying the need to
reverse the trends; A list of potential large-scale alternatives to reverse undesirable trends
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Next meeting date
The next joint (Strategic Planning Team and Science Panel) meeting will be on
Wednesday, June 8th from 9:30 a.m. – 4:00 p.m. at the Elkhorn Slough Reserve.
The main purpose of the meeting will be to discuss the feasibility of potential largescale alternatives to reverse undesirable hydrological trends.
A. Review outcomes of last meetings/Update on status of draft documents
1. There was a request to post conceptual model with the other draft documents on the
Tidal Wetland Plan web pages.
2. The draft document Geology, Geomorphology, Hydrodynamics, and Inlet Stability of
Elkhorn Slough that was written by Sea Engineering is currently under review.
3. It might be helpful to have a working group meeting with Sea Engineering to discuss
the details of what the tables and graphs mean and discuss their findings in person.
They would be happy to present at a meeting once the document is finalized.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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B. Produce statements predicting likely trends
Below are consensus statements predicting 50-year trends for tidal habitats with
unrestricted flow in Elkhorn Slough.
DRAFT 50-Year Prediction Statement
(1A) Channel depth will continue to increase at approximately the same rate (average
trend for the past 20-50 years) in the lower Elkhorn Slough.
FINAL DRAFT 50-Year Prediction Statement
The Elkhorn Slough system is not at equilibrium. Therefore:
(1A) The cross-sectional area will continue to increase significantly in
the lower main channel of Elkhorn Slough.
1. Is there any suggestion from the Sea Engineering analysis that deepening will
continue uniformly, or might the deepest spots be done getting deeper? Some of
these areas might get wider while other areas might get deeper so understanding the
spatial patterns of deepening are important for corrective measures.
2. Change “channel depth” to “channel cross-sectional area”.
3. Do we need to take into account sea level rise, or is it minor compared to erosion
effects? Seems like it is more of a minor cause right now.
4. Concerns about non-linearity – it might be contrary to predict a uniform rate of
change. Delete the rate for now until we have time to better quantify the rates.
5. We need to add wording then to capture the fact that the rate would be worrisome
enough to motivate management.
6. It is possible for the Kvitek lab to at least come up with a five-year projection of
bathymetric changes, but these estimates would be conservative.
7. If we want to come up with 50-year rates, the predictions could be a range of
projections.
DRAFT 50-Year Prediction Statement
(2A) It is unknown if channel depth will increase in the upper Elkhorn Slough.
FINAL DRAFT 50-Year Prediction Statement
(2A) The cross-sectional area of the main channel will likely increase in
the upper Elkhorn Slough. The erosion rate is currently less than in the
lower Slough, but will likely increase over time.
8. Is it worth making a distinction between the upper and lower Slough?
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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9. There will likely be an increase in erosion in the upper Slough but at a lower rate than
in the lower Slough. The upper Slough can be defined as the area from the Parsons
Slough mouth to Hudson Landing.
10. That boundary seems to be shifting, but the distinction between upper and lower
could be important for management activities.
11. There seems to be a break between the lower and mid-slough in channel erosion rates
so it could be further separated as needed.
12. More recent bathymetric analyses by Edwin Dean and Josh Sampey in Rikk Kvitek’s
lab suggest that erosion in the mid-slough is less than what Dean’s earlier graph
shows.
13. Erosional features continue all the way up past Kirby Park – there is a coarsening of
sediments in those areas.
14. Bank erosion from wave action seems to be a more important contributing factor in
the upper Slough.
DRAFT 50-Year Prediction Statement
(3A) Channel width will continue to increase at approximately the same rate.
FINAL DRAFT 50-Year Prediction Statement
(3A) Bank erosion will continue (and may accelerate in the upper
Elkhorn Slough) causing significant marsh loss.
15. There is concern that subtidal widening is different than intertidal widening so
narrowing this statement to bank erosion would be more accurate and clear.
16. It is important to identify the variation by region of the Slough.
17. We might need to look at the different processes for the main channel and tidal creeks
at some point.
DRAFT 50-Year Prediction Statement
(4A) Mudflat habitat will continue to increase at approximately the same rate
(conversion from salt marsh/tidal creek habitats).
FINAL DRAFT 50-Year Prediction Statement
(4A) The aerial extent of mudflat will continue to increase at the
expense of salt marsh.
18. There was a bit of concern that this statement might not convey the idea that salt
marsh might also be converting to subtidal channel habitat.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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DRAFT 50-Year Prediction Statement
(5A) Mudflat habitat along the channel will also decrease (convert to channel)
but at a much slower rate than what is gained from salt marsh/tidal creek habitat
conversion.
FINAL DRAFT 50-Year Prediction Statement
(5A) Sediments in soft-bottom areas exposed to strong tidal currents
will erode, leaving harder substrates with larger grain sizes and
weight/volume ratios (bulk density).
19. Mudflats have been experiencing deposition in areas that are flanking eroding
subtidal areas from 2001-2003 according to Kvitek’s bathymetric data. The areas
north of Kirby Park have had some losses, but the rest of the Slough has had gains.
Rikk Kvitek will feel much more confident after the summer 2006 resurvey.
Different vertical controls were used in 2001 and 2003 (different tidal models), but
will be the same in 2003 and 2006.
20. The observations from John Oliver are that mudflats have deepened on northwestern
side of main channel. You can take a boat up next to the bank in areas where you
used to get stuck, Vierra’s mudflat is also eroding away, and the firmness has been
increasing changing the shell beds.
21. There might be a way to merge the ideas above with a new statement that captures the
“hardening” of soft areas.
22. There needs to be a way to capture the fact that this is occurring in only some of the
mudflats.
DRAFT 50-Year Prediction Statement
(6A) Tidal creeks will continue to increase in width and depth at approximately the same
rate.
FINAL DRAFT 50-Year Prediction Statement
(6A) The aerial extent and cross-sectional area of tidal creeks will
continue to increase at the expense of smaller tidal creeks, salt marsh,
and mudflat.
23. There was a question about whether number and the sinuosity of tidal creeks have
changed as well as size. Yes.
24. There was a desire to include the fact that we will lose higher order creeks, but there
is no data from the past to support the fact that this happening even though it seems
possible in future.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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25. There was some concern about what will happen with tidal creeks – will there be
more or less smaller tidal creeks. There would be less as the creeks widen and merge
together in the short-term, but smaller creeks might at the same time be created in
new areas so the overall net aerial extent might be similar. It could also be helpful to
figure out if tidal creeks would be less sinuous in the next 50 years.
DRAFT 50-Year Prediction Statement
(7A) Salt marsh habitat will continue to decrease (convert to mudflat) at approximately
the same rate.
FINAL DRAFT 50-Year Prediction Statement
(7A) The aerial extent of salt marsh will continue to significantly
decrease and convert to mudflat and tidal creeks.
26. No general comments about this statement as the ideas are very similar to 4A.
DRAFT 50-Year Prediction Statement
(8A) Formerly diked and subsided salt marsh habitat suddenly exposed to tidal
flow (failing levees) will convert to mudflat at a higher rate than other areas.
FINAL DRAFT 50-Year Prediction Statement
The group decided not to have this statement.
27. There was a discussion that there are not that many remaining formerly-diked areas
that are likely to get exposed to more tidal flow in the future (Estrada, Porter are the
only big areas).
28. There is some value in showing that you want to prevent full tidal flow into places
where it is limited now because it would increase tidal prism and tidal erosion
problems and may turn these areas into lagoons if there are subsided.
29. It is important to capture this statement in management planning, but maybe not as
part of the predictions.
General Comments
30. It is my expectation that over the next 50 years the system may go past the tidal flat
stage and actually be dominated by shallow subtidal habitat (Josh Collins, 6/2/05).
C. Create a list of possible biological responses associated with trends
This agenda item was postponed to a later date as some of these experts were not able to
attend today’s meeting and the work may be more suitable for a smaller working group
meeting.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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D. Discuss the justification for reversing the trends
Now that there was consensus on the 50-year trends, the group was asked why those
trends should be reversed.
Conversion to more subtidal habitats (invasive species, estuarine-dependent species,
conserving existing good quality habitats)
1. It is important to enhance estuarine-dependent species versus more common marine
species.
2. There is no good reason to let good-quality intertidal habitat erode away.
3. A basin or lagoon with more subtidal areas would have more introduced species and
degraded benthic assemblage. There has been a doubling of invasive species in the
change from soft to hard substrates (such as on mudflat habitats).
4. It is an evolved mature habitat and we don’t know if we’ll have the same highly
evolved system as it changes to more of a marine system. There is too much
uncertainty of what we might end up with if we let the trends continue for the next
hundred years and we know the importance of conserving existing habitats.
5. It is important to preserve biodiversity supported by a diverse mix of habitats.
6. Some species of special concern are dependent upon the habitats we are losing and
even if we gain new animals, conserving the historic mix is important.
7. It is an important transitional migratory area so the conservation of large areas of
different estuarine habitats is important. Elkhorn Slough is a stopover or stepping
stone between other estuarine habitats north and south of here.
8. More intact marsh habitats protect the water quality of Monterey Bay by acting as a
buffer for agricultural and non-point runoff.
Historical mix of habitats
9. Value historical mix of habitat regimes of 200 years or more ago.
10. A 150-year timeframe might better if you consider diversity as the system might have
been more dominated by freshwater inputs at that time when the mouth was seasonal
closed with a sand bar. A drowned river mouth has more diversity than a closed
estuarine system.
11. A 200-year timeframe would capture pre-large scale human impacts such as the
railroad.
12. It has been a salt-marsh dominated system for a long, long time.
Regional Loss
13. Understanding regional loss is important. Salt marsh habitat has faced the highest
percentage of loss of any estuarine habitat in the nation.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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Socio-economic
14. We made a decision to create and keep the harbor mouth open so we need to mitigate
for that decision.
15. Decrease the likelihood of a major railroad catastrophe.
16. There is some watershed support to reduce the tidal influence.
17. There could be socio-economic impacts (Carrie Pomeroy at UCSC’s report on
coastal-related activities could help shed some light on this).
18. Elkhorn Slough is less urbanized than many salt marsh habitats in other areas so we
have a chance to preserve “high quality” habitat compared to other areas with more
urbanization-related toxics and problems. There has been a lot of conservation work
in the upland watershed to decrease the threat from development and other threats so
this system is a lot more protected than different areas and the other threats are
potentially controllable.
19. It is our social responsibility because some of these areas are in the public trust as
they are designated as federal and state reserves and federal sanctuary.
20. Intact marshes and creeks have fewer mosquitoes so health concerns such as West
Nile might be lower.
E. Brainstorm potential large-scale alternatives to reverse trends
The purpose of the brainstorm session was only to collect initial ideas about potential
large-scale alternatives, not to evaluate them at this time.
Reducing the tidal volume – tidal flow restriction
1. Mute the flow to Bennett Slough by reducing the number of culverts and to the Old
Salinas River Channel by adding tide gates or some other structure when the road is
improved in order to decrease the overall tidal prism.
2. Mute the flow at the Parsons Slough mouth with some sort of partial sill, tide gates,
and/or inflatable dam to reduce the tidal prism.
3. Create a barrier part of the way up the Slough to mute part of tidal flow maybe near
Hummingbird Island or Parsons Slough. This structure would not have to be closed
all the time.
4. A sill across the channel could be concrete on the bottom with a rubber dam (similar
to what they use for river management) that is blown up at the surface or reduced to
2 meters below surface and only inflated to reduce prism during spring tides, etc.
Reducing the tidal volume – sediment additions
5. Importing fill would help reduce the tidal prism. Deeper fill could be rockier and
then it could be topped with softer sediments down to about 1 meter in depth which
would be the depth that most clams would need.
6. Building up Parsons Slough by adding about 2-3 feet with sediment would reduce the
tidal prism by half or more in that area.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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7. All of the land east of railroad tracks has been subsided by diking and draining so all
of these areas would benefit from sediment additions which could enhance marsh
vegetation and reduce the tidal prism.
8. Sand could be used as an ephemeral dam in the channel.
9. Is there a way to capture the sediment near the mouth and pump it in a circle back
into the Slough?
10. Sediment entrainment was a serious proposal for the Mississippi River to stop
wetland erosion.
11. Pump beach sand into a straight stretch of the main channel above mean low water to
mimic pre-stabilized harbor mouth approximately 1/4 mile up the channel with the
synthetic action of a pump. The pump could be operated on the flood and not on the
ebb tides.
Possible sediment sources
12. Sediment could be supplied from the watershed. Take the dam out at the head of the
watershed (around Muertos Canyon, 250-feet high) or truck in that sediment.
13. Redirect the Pajaro River (enhancing habitat for salmon) so that in flood years, the
sediment would enter Elkhorn Slough. Another option would be to pump sediment
in from the Pajaro River (right now bulldozers are used to pile this sediment up on
the levees).
14. Beach sand could be a source of sediment – it would come in from longshore
transport anyway.
15. The Harbor dredge materials could be used if they are too toxic. The permitting
dredge disposal of Harbor sediments should be done fairly soon – it is done about
every two years.
16. The sediment needs to be mixed with organics. In order to get healthy plant growth,
the sediments need to have relatively high nutrients and beach sand is not so great,
but this sediment could be mixed or layered with other sources. You could also add
kelp, manure, etc. to the dredge sediments or beach sand to get the right mix.
Modifying channel shape and flow
17. Remove the fill under the Highway 1 Bridge (west of bridge) to make it wider to
increase the bottom friction and reduce velocities which might allow more sand to
settle near the deep scour holes (such as near the Wildlife Management Area).
18. Increase the sinuosity and roughness of the main channel. This could help reduce
velocities and erosion.
19. Try to promote the establishment of eelgrass which could help trap sediment and add
roughness to the channel to decrease velocities. This could reduce the tidal prism.
20. Connect Seal Bend to Bennett Slough around the Wildlife Management Area to add
another way for tidal water to enter and exit Elkhorn Slough. This might help
maintain the tidal prism.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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Reducing bank erosion
21. We need to have some traditional engineers to help come up with solutions to reduce
bank erosion such as groins, jetties, and rock and concrete structures.
22. Logs and root wads could be used to help stabilize banks and are less unsightly.
Eucalyptus trees would be good source for logs.
Restoring the Elkhorn Slough mouth location and/or cross-sectional area
23. Create a partial sill under the Highway 1 Bridge to reduce the tidal influence.
24. Redirect mouth so that it enters Monterey Bay by the old Salinas River mouth (by
Bennett Slough) as it had done historically to increase sinuosity and reduce the crosssectional areas of the mouth to reduce the tidal influence.
25. Move the harbor to a different location and remove the jetties to let the sediment fill
in the mouth to a smaller size to reduce the tidal influence.
26. Create a lock and dam structure under the Highway 1 Bridge at the mouth of Elkhorn
Slough to decrease the volume of tidal influence. Power generation from turbines
that could slow the tidal flow could be a possibility.
General comments about potential large-scale alternatives
27. Smaller-scale pilot projects seem to be a good stepping stone to see how these
actions would change the system.
28. It would be good to identify other places were there is a potential to modify tidal
flow such as North Marsh and Azevedo Ponds where there are existing tide gates or
culverts.
29. Try management scenarios that would affect each part of the system so there is a
reverse feedback loop to see what works and what doesn’t.
30. Sediment addition and building structures seem to be two different ways to restrict
tidal flow.
31. Need to compare the economic costs of each alternative.
32. We need to have some engineers attend the next meeting from some consulting firms
and agencies to help come up and understand how each alternative could work.
33. Some of the alternatives only take care of part of the problem. We will likely need to
do several projects simultaneously to see an affect.
34. We could use arrows to indicate which of these are pilot projects.
35. Some alternatives could be testing using models before they were actually put in
place.
36. What is the final product going to look like? It is a matter of timing, but it will be as
fine a grain as we can get with the funding and time constraints, but will definitely
have a list of preferred management alternatives.
37. It might be helpful to circulate the document that Sean Anderson completed about
possible management alternatives from Louisiana, the Mississippi River, and the
East Coast. There are not as many case studies that are applicable to this system –
most folks are trying to get rid of sediment.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
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38. Kerstin: what are the trends of the areas and would one want to alter them if possible
or if we could? What are trends and why do we care?
39. It would be great to eventually host a summit for all the wetland management plan
processes in the area so that everyone knows what everyone else is doing.
40. We need to hold a working group meeting about restricted flow areas.
41. It would be great to have 1-pagers about restoration over the past 20 years or so at
the Slough to see what has been tried and what resulted, particularly for restricted
flow areas.
F. Set next meeting date and potential discussion topic
The next joint (Strategic Planning Team and Science Panel) meeting will be on
Wednesday, June 8th from 9:30 a.m. – 4:00 p.m. at the Elkhorn Slough Reserve. The
main purpose of the meeting will be to discuss the feasibility of potential large-scale
alternatives to reverse undesirable hydrological trends.
Possible next steps
1. A first step could be to refine the alternatives to determine the likely hydrological
outcomes. For example, would “Alternative A” really reduce the tidal prism? If so,
what would happen with tidal velocities? We also need some time to consider
integrating alternatives such as, “Alternative A + Alternative B”.
2. Once the alternatives are narrowed down based on likely hydrological outcomes,
then we need to predict the likely physiochemical and biological outcomes.
3. The third step could be to evaluate how each alternative meets the goals (need to be
defined soon) for the Tidal Wetland Plan (the Strategic Planning Team is working on
defining these goals which will be reviewed by the Science Panel).
4. A fourth step would be creating different criteria to evaluate the pros and cons of
different alternatives such as risk of unintended consequences, cost, impacts to
human use, etc.
5. Once we have a list, then we could rank these alternatives and then start talking to
the public about the preferred alternatives.
DRAFT Joint Science Panel and Strategic Planning Team (April 13, 2005) Meeting
Summary, Elkhorn Slough Tidal Wetland Plan
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