PESCADERO MARSH FISH DIE-OFF

PROPOSED MITIGATION MEASURES

December 2009

Proposal:

In order to reverse several negative consequences in the Butano Marsh area due to hydrologic modifications made by DPR, a return to some conditions need to be met before the fish die-off proposition is proposed.

This includes:

1. Adding baffle culverts under the Butano pedestrian bridge.

2. Replacing the non-functioning adjustable culverts in the North marsh.

3. An increased Creek flow into Butano channel is proposed.

4. A long term monitoring study is proposed.

*A Lake and Streambed Alteration Agreement Application for project #1 has been submitted on behalf of the Native Sons of the Golden West as the Operator conditioned on the permission of the landowner to trespass. These are interim mitigation measures to reduce negative effects until the long-term plan is revised.

Background:

An annual die-off of fish and other aquatic fauna has been documented by the Department of Parks and Recreation (DPR) and local fishermen in Pescadero Marsh. According to various local fishermen who frequently fish the lower marsh area, this event was first noticed in 1995 and for other years since, but not before (Tim Frahm; pers. com.). Direct observations by DPR staff and consultants, fishermen, and others, indicate that the die-off occurred each time in conjunction with the late fall, early winter breaching of the beach sandbar which forms each year. The bar may briefly form and break (days to weeks later) in spring or early winter without producing a visible effect for casual observers.

The sandbar breaching and outflow of elevated marsh waters to the ocean can occur at a time when the marsh is populated by steelhead juveniles, including fish of smolt size and coloration. Jerry Smith (CSU San Jose) conducted studies in the marsh between 1985 and1989 to determine the relationship of the sandbar formation to fish habitat and described the importance of an early and stable bar formation for fish populations.  Smith did not observe nor did he report fish kills during this time period, except for a late spring kill in the open lagoon in 1986 due (reportedly) to pesticide runoff.

Prior to the problems noted, DPR conducted several years of studies by consultants to determine the best changes to make to the marsh following their purchase of private lands. After an extensive public review process and permitting agency input several modifications were made to circulation patterns in the Marsh (it should be noted that recently one of the biologist consultants of this process said publicly that they “got it wrong” with their recommendations).

The first die-off was noted in a DPR report following a December 8, 1995 breech with several hundred steelhead trout counted. A kill was also confirmed by DPR in 1997, but the time of breeching and numbers affected were unknown. The bar did not form in 1999. The next DPR confirmed fish kill was 2001 with approximately 30 fish counted and a die-off repeated in 2002 with small numbers of steelhead counted, but numerous starry flounder and crab. In October 2003, approximately 300 10 to12 inch steelhead trout YOY (young of the year) were casualties counted by DPR staff and local observers (Tim Frahm, Simms Pers. com.). At that time a significant hydrogen sulfide smell was noted in conjunction with the outflow of water.

During 2004, the die-off was anticipated and the sand bar was patrolled by DPR and several local citizens. The bar formed and breached on May 15^th without noticeable effect and the final breech occurred on Dec 5^th with a significant die-off of steelhead, starry flounder, crab, stickleback, staghorn sculpin, and smelt (sp) totaling 350 as counted by DPR staff (Sloan).

Since 2004 up to 2009, a die-off was noted by local fishermen each year when the sand-bar breached, including a 2006 event where 180 photos of individual dead juvenile steelhead were taken by a local resident. Each year presented less than stellar visual conditions such as a night time breaching or strong outflow currents that removed evidence.

Observations Assumptions and Inferences:

The following is intended to provide a basis for discussing the proposed actions. There have been many observations made and opinions offered by others to explain the cause of aquatic die-off during the sand bar breach in late fall.

*Below is a partial list from a defined period which is not intended to exclude or detract from other theorists or observers:

• A possible direct connection to the Caltrans modification exists due to a widening of the passage and removal of supports under the Highway 1 Bridge. This may cause the sandbar to form later in the year. This would result in less time for fresh water to convert the lagoon from ocean influence. A change to sandbar dynamics is supported by the recent formation of a reverse delta in the lagoon from sand that otherwise would have added to bar formation and mouth closing.

• Noticeable fish kills are assumed to take place following the late fall sandbar breach. 2001, 2002, 2003 and 2004 observations of the die-off’s timing support this hypothesis. The inference is that the process of lagoon water outflow and/or water quality at the late period breech has changed in the last few years. Because fish kills were noted following the DPR projects the operating assumption is that the fish kills are unintended consequences of those actions. The most likely changes leading to negative conditions are Hwy 1 bridge modifications, lack of DPR management plan operation and the new levee openings. Additionally, lower inflow of fresh water from upstream diversions could play a part.

• Fish will occupy areas with low DO in deeper water if surface waters remain oxygenated (Smith, 1986 observation). This appears supported by the low oxygen levels measured up to one to three feet below the surface for the areas of fish kill. Fish in this area were probably healthy and actively feeding in the main lagoon based on stomach examination, size and color of the carcasses.

• It is assumed that fish were occupying the area where the bodies were documented and some carried away by current. This is supported by the fact that fish were not noticed at high tide after the breach until the low tide levels. Presumably, carcasses had a chance to sink to the bottom where they were less susceptible to currents. Also, fish found in the weeds (away from the current) were proximate to those found on the shoreline indicating lack of movement (see pictures). However, fish still in the water column could have been carried out of the lagoon and deposited on the beach. Many dead fish were noted on the beach outside the marsh in 2003 and 04.

It is very possible that the documented numbers represent a minor part of those affected. The murky conditions after the break prevented counting carcasses under water, ebb tide flows could remove dying fish in the water column from the lagoon, and scavengers probably removed substantial shoreline evidence.

• Wind effect in the lagoon can significantly increase water column oxygen levels except below strong stratification. Areas protected from winds such as Butano and Pescadero channels (shaded by levee and/or riparian vegetation) persist in low oxygen levels throughout the water column (Sonde data). Strong winds may also play a part in reducing the sandbar height prior to breaching and affect the timing of the opening event (observed by Steele).

• The sandbar appears to erode slowly once the process begins by overtopping and then picks up speed as the flow velocity increases. It’s been suggested that the draining of top water first may reduce available space for salmonids as high DO waters drain way. This is suggested by the BU7 Sonde.

• Observers on site following both the 2003 and 2004 sandbar breaching indicated that a strong smell of hydrogen sulfide came from the back marsh such as the North Butano Marsh and North Marsh. These areas are normally not flooded until the sandbar forms. The smell was also directly associated with turbid water consistent with dark, fine sediment noticed on the Butano channel bottom. Steele and others noted strong HS smell when bottom sediments were stirred in the North Butano Channel using a pole. HS could be the reason that fish die quickly following the sandbar breach.

One hypothesis is that changes to the hydrology, and breaching or enlarging openings of certain levees has increased the velocity and volume of  low DO, high BOD and HS of back marsh water entering the main lagoon area where fish are holding when the pond drains following sandbar break. This is exacerbated by certain conditions not present historically when tidal gates kept salt water from irrigated fields. With gates installed, the back marsh was only flooded with fresh water during winter flood events and sandbar formation. Now, the opening of the North Butano Marsh (under the pedestrian bridge) levee without the gates allows salt water to enter the deeper channel of that marsh and remain trapped creating the stratified effect and resists wind mixing. This heavier, salty bottom water will trap heat, become anoxic and high in HS from decomposing vegetation (fall seasonal pond weed die-off) and resists mixing more than fresh water. This anoxic pool will become mobilized only during sand bar formation causes the area to flood and then later drain rapidly. Rain caused freshets intensify this stratification in the creek arms. When the bar breaks, anoxic bottom waters (and high BOD organic sediments) quickly mix with surface waters causing a sudden DO depletion throughout the water column.

Additionally, the DPR changes to improve circulation may have increased the scour potential and mobilized bottom sediments during the outflow of lagoon waters at their largest flood stage. Basically, the breaching of levees and widening/deepening of breaches has enabled back marsh areas and the artificial channels along the outboard side of the levees to drain more rapidly into the creek and lagoon area.  This connectivity did not exist or was minimal prior to restoration work, and was probably the most significant modification undertaken.  This theory is strongly supported by observing that (1) prior to bar break the lagoon water column was tannin colored, but free of suspended particals. (2) the sandy bottom sediments in the main lagoon did not contribute to the turbidity at bar break, and (3) the North Butano marsh channel bottom consisted of black fine sediments similar to turbidity in the lagoon water column. It was also observed that the very large volume of water normally not in the back marsh drains through the levee opening at a higher velocity than water moving down the shallower main Butano channel. This effect was not measured metrically when observed but noted by watching floating objects and movement of darker sediment laden bottom water.

• The WL Sonde data and observations seem to support that the pedestrian bridge area is one mixing zone for back marsh and main channel waters. In addition, the location of steelhead carcasses in both 2003 and 2004 suggests that the area between the pedestrian bridge and main lagoon is a lethal area at the time following bar break and points to influence from this widened levee breech.

Recommendations and proposed project:

The first is mentioned in the Application as the Project.

*Any or all four of the measures could be permitted by the agencies or be used for discussion.

Mitigation Measure #1:

The DPR management plan was not operated as permitted which is evidenced by the never-operated tide gates, and the levee openings had unexpected consequences as described above. Adaptive management or mitigation measures added to flawed planning is a common reaction to negative consequences. Unfortunately, neither of these has been attempted by DPR and they have resisted any changes unless there are more studies (but at least one attempt to block the exit of Butano Marsh water using bladder dams was attempted in 2007/08 by other agencies and the public). Also, the lack of performing the conditions of the permitted management plan appears to be a violation of the ESA because of the loss of listed individuals. In any event, listed species have been affected in a way that should cause alarm in the permitting agencies (even without the information required by DPR). A return to conditions prior to the project which did not cause loss of listed species is in order at least until the desired information is obtained to redo the management plan. If the permitting agencies have recognized and permitted the use of bladder dams under the pedestrian bridge an even more focused mitigation attempt should be, and is, proposed here.

A return to tide gates at the opening under the pedestrian bridge will keep high tide salt water from entering the deep channel in the Butano Marsh but allow fresh water to enter from upstream. By providing a significant number of gates, flood water would not back up and would thereby relieve flood pressure on the Pescadero Road Bridge as envisioned in the management plan. Although the fire-hose effect at sandbar breach would not be diminished, the water quality should improve for tide water gobi in the channel as well as reduce the effects of salt water stagnation on salmonids. The velocity of the water would also be located higher in the water column lowering the potential for bottom scour in the channel.

Drawing one depicts the Butano Marsh Levee opening at low tide. The deep channel behind this opening traps salt water and holds it until the bar breaks. Drawing two shows flap installed culverts preventing water from entering the channel during high tide. This is a concept drawing for the purposes of the permit and a detailed construction drawing can be provided as a condition of the permit.

The monitoring effort of the old project was not adequate to achieve sufficient direction to DPR so additional focused monitoring should accompany the above approach. Water Quality sampling in the area behind and in front of the gates during and after sandbar influenced flooding should be at least the minimum required. Details of this monitoring can be proposed as needed.

CEQA: No extraordinary permit process is necessary by this approach other than the circulation of a NegDec to agencies for comment. No listed species will be harmed similar to the conditions that existed prior to State Parks acquisition. Mitigation measures to reverse unintended consequences are not new projects but mitigation as an extension of the old project and do not require an extended public review. This has already been demonstrated by the agency sponsored bladder dam attempt. This can also be considered a repair of an existing facility, i.e. a levee breech.

Mitigation Measure#2:

The original tide control gates in the North Marsh were never operated and are in disrepair. If these are still important features in the DPR plan they should be replaced with culverts operating similar to those proposed under the Pedestrian Bridge. Automatically operated gates are needed to offset the lack of DPR maintenance capacity. This is a change from the management plan that was to adaptively operate the gates in response to conditions. Again additional construction drawings can be provided specific to the project as a condition of the permit.

CEQA:

*This is a maintenance or repair of an existing facility and can be covered under exemptions #15301 and #15303 et al.

Mitigation Measure #3:

Presently the Butano channel sediment processes have raised the level of the channel bottom to higher than the Butano Marsh channel. This creates a lip under the bridge and increases the low area affect of trapping salt water at high tide. The levee toward the upstream of the marsh was breached to increase creek flow into the Butano Marsh channel from the upper end but the desired effect was not accomplished. If creek flow could be directed through even larger openings at the upper end of the levee in such a way to direct Butano sediments into the channel, this deep channel condition would eventually fill in similar to Butano Creek. The flow of sediments into the Butano channel would also lower the sediment deposit under the Pescadero Road Bridge at least for the short term.

An alternative to the above is to suction dredge sand from the downstream area into the channel to remove the saltwater trapping potential. The Bridge would have to be removed and the breach widened to reduce the fire-hose effect caused by the large flooded area of Butano Marsh being empted after the breach. Dredging sand would lower the effects of turbidity.

CEQA:

*This is an adjustment to the original plan to achieve the effect of filling in the deep channel in the marsh which would be beneficial and more natural to the marsh. But there also could be unintended consequences of changing the flow as was the situation caused by the DPR plan. A specific plan would have to address these potential consequences.

Mitigation Measure #4:

Future long term study plans would benefit from having a clearly stated hypothesis based on past data inferences and observations rather than the random approach to this point.  The study would then outline data gathering efforts based on predicted outcomes. Focus of future studies should be centered on the WQ conditions of the marsh immediately prior to bar break as well as the flow dynamics and WQ conditions during and following the break. The discussion for this approach should begin now between permit agencies responsible for the affected listed species and DPR. DPR has not demonstrated the objectivity needed to manage data design, gathering or interpretation based on the previous efforts. A combined agency/public approach would be more credible.

Below are some discussion topics for such an effort.

Hydraulic modeling of slough and creek channels during these special flood stages;

Observation of flow dynamics during tidal exchange in and out of the back marsh areas;

A continuation of spot water quality sampling during lagoon formation, including the marsh flats to ascertain processes occurring there;

Setting up an alarm to alert trained observers when the breach occurs so that direct

observations can be made (the nature of these observations should be determined
well-beforehand and coordinated)

A collection of WQ samples during the breach using automated devices;

Getting a permit to collect fish during the breach and submit them for autopsy, if there are autopsy techniques that would confirm H2S poisoning as well as conducting bioassay tests of the water.  If possible seine for fish during the breach for observation without waiting for them to die before collection.