Ecological Management Action Plans

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EM-6 Shoreline Stabilization and Induced Sediment Deposition

EVALUATION METHODS

• Use shoreline stabilization in areas where shoreline erosion is a problem and the use of sediment inducers is impractical or infeasible due to project locality, cost, and/or the lack of available total suspended solids.
• Use sediment inducers in high wave energy environments to reduce wave energy and allow total suspended solids in the water column to settle.
• Use sediment trapping in lower wave energy environments to improve sediment deposition and prevent sediment re-suspension in shallow water bodies in interior marshes which cannot infill because of wave fetch.

Many techniques/tools can act to both stabilize the shoreline and induce sediment deposition.

No implementation plan was recommended for this Action Plan due to the lack of a reliable source of funding for these projects and the general high cost of shore protection.

The effectiveness of any individual project in shoreline stabilization (SS), inducing sediment deposition (SI), or trapping sediment (ST) should be evaluated according to the following criteria. Specific criteria may vary depending upon the characteristics of individual projects.

• The rate of shoreline erosion is halted or reduced (SS, SI).
• Wave energy is reduced (SI).
• Sediment accumulation is increased (SI, ST).
• Elevation of water bottoms increases (SI, ST).

Steyer and Stewart (1992) list variables which may be measured to monitor shoreline protection and sediment trapping projects implemented under CWPPRA. Their assessment does not identify sediment inducers as a separate approach from sediment trapping. It is recommended that this model be followed, whether or not any particular project is funded by CWPPRA. Measurable parameters identified by Steyer and Stewart (1992) have been revised and prioritized by Steyer et al. (1995) into Essential Variables or Additional Variables or Substitutions as shown in Table EM6-xxx1. These have been assigned a priority for monitoring under the CCMP Action Plan. The priorities have been assigned based upon the broader mission of the CCMP compared to CWPPRA (restoration, creation or enhancement of vegetated wetlands is not necessarily the primary goal of CCMP Action Plans) and the objectives of the projects as described in the Action Plan. However, priorities for monitoring variables may vary based upon the characteristics, objectives and design of individual projects.

Table EM6-xxx1. Steyer et al. (1995) classification of monitoring variables for shoreline stabilization and induced sediment deposition.

^a Includes species composition and relative abundance

In addition, it is recommended that monitoring of projects classified as sediment inducers, should specifically include measurements of wave height and period, as the reduction of wave energy is the primary means by which sediment inducers increase accretion and bottom elevation. Associated measurements of wind speed and direction should be made to allow assessment of wave forcing in relation to project effectiveness. For these projects, these parameters should be assigned a priority above vegetative and habitat assessments.

This section provides guidance on the types of data collection methods which are currently available and appropriate for monitoring these types of projects. There may be alternative existing or new techniques which could be adopted as long as they confirm to the data quality objectives described under QA/QC.

Habitat Mapping - The procedures and methods outlined by Handley (1992) and Steyer et al. (1995) should be followed.

Vegetation - Species composition and abundance should be measured using the Braun-Blanquet method as described by Steyer (1992) and Steyer et al. (1995) with the qualification that appropriate training be provided to ensure consistency between individual=s assessments of abundance.

Bathymetry/Topography - Bathymetry and topography should be measured using the techniques outlined by Powell (1992) and Steyer et al. (1995) noting that recording fathometers, measuring in m, should be used for bathymetric surveying with either GPS or conventional rod-and-level techniques recommended for topographic surveying. The choice of survey techniques should be determined by the acceptable level of error and the sophistication of the available technology and equipment.

Total Suspended Solids - Various methods for measurement of total suspended solids concentration are described by Powell (1992) and Steyer et al. (1995). The difficulty with point measurements is their inability to resolve vertical and horizontal variations in the total suspended solids field, as well as temporal variations in total suspended solids concentration. Water samplers should be used in conjunction with deployment of sensors which continuously monitor suspended solids concentration (e.g., Downing and Beach, 1989). Deployed sensors must be regularly serviced to prevent fouling (as described by Powell (1992) and Steyer et al. (1995)).

Shoreline Markers - Shoreline markers should be used to assess changes in the position of the shore over time. This information may also be obtained from the bathymetric and topographic surveys of the project area. The procedures of Letzsch and Frey (1980) can be used to document changes in the marsh margin in the area impacted by the project, and the reference area. Details are described in Steyer et al. (1995).

Wave Activity - Measurements of waves are not addressed by Steyer and Stewart (1992). Measurement of wave height and period requires the deployment of water level sensors (i.e., pressure transducers) which can record water level changes at least a frequency of 5 Hz. The selection of sensor type is critical, as the type of water level variation expected in the project area due to waves (frequently less than 0.5 m in areas where sediment inducers are deployed) must be detectable. The best range for pressure transducer sensitivity is 0-2.5 psi or 0-5 psi, depending upon the project environment.

Wind Speed/Direction - Automatic wind speed and direction equipment should be used to measure this parameter, as described by Powell (1992) and Steyer et al. (1995). Sensors should be placed at a standard height above the ground (e.g., 2 m or 10 m) in order that data can be compared to data collected by the Louisiana Office of State Climatology for various sites in BTES.

The sampling design for monitoring project effectiveness must include comparison of the project area with an appropriate reference area. Monitoring projects without the use of a reference area can lead to misinterpretation of monitoring data through the lack of a comparative site to identify natural interannual changes in marsh processes, and/or other difficulties (Steyer et al., 1995). It is necessary to ensure that reference and project areas are comparable. Both project and reference areas should be divided into marsh habitats and replicate samples randomly selected within each habitat type. Comparison between project and reference areas should then be based at the sub-area or habitat scale (e.g., brackish marsh sub-area in project is compared to brackish marsh sub-area in reference areas). If it is impossible to select a suitable reference area, as may be the case with large shoreline protection projects, then either pre-project monitoring or baseline monitoring (Steyer et al., 1995) may be adopted as an alternative. Both of these approaches reduce the validity of the monitoring results as the monitoring then fails to account for natural interannual variability in erosive/depositional processes.

The size of the project area, the number of habitats/environments included in the area, and heterogeneity of those habitats/environments determine the number of samples which need to be taken and the validity of the statistical analyses. Steyer et al. (1995) describe appropriate procedures for the determination of sample size within the project area. The use of parametric (e.g., ANOVA, Student=s t-test) or non-parametric (e.g., Mann-Whitney U-test, Kolmogorov-Smirnov test) statistical procedures will depend upon the character of the datasets. If data are not normally distributed, as may frequently be the case with the collected data (e.g., salinity in a fresh or intermediate marsh), then transformations, such as logarithmic and square root transformations, should be applied and the transformed data tested for normality. If a normal distribution cannot be achieved in this manner, non-parametric tests should be pursued. The most basic statistical design for project evaluation is a two-tail test of whether the mean value for a measurable parameter within the project areas is equal to the mean for the reference area. If inequality is identified, further analyses can then determine if the effect of the project is to increase the parameter or decrease the parameter.

Estimated costs for evaluating shoreline stabilization and sediment trapping projects have been developed for CWPPRA by Steyer and Stewart (1992). The actual costs depend upon the size of the project and the number of stations sampled/samples collected. These estimates have been revised where possible in consideration of the recommendations presented here regarding measurable parameters and data collection methods. Ranges are presented for cost estimates on an annual or per sample basis (Steyer and Stewart, 1992) in Table EM6-xxx2.

Table EM6-xxx2. Cost estimates for monitoring shoreline stabilization and induced sediment deposition projects.

^a Includes bathymetry, topography and wind speed/direction.

^b Includes species composition and relative abundance.

^c Includes bathymetry and topography.

Cost estimates for shoreline markers are $150-300 per measurement (Reed, 1992). The deployment of two sensors to detect wave height and period would be approximately $12,000 in the first year (including instrument acquisition) and $4,000 in subsequent years. Estimated costs for total suspended solids sampling are approximately $14,000 in the first year (including instrument acquisition) and $4,000 in subsequent years. For projects implemented by CWPPRA, average annual monitoring costs shall not exceed $2,150 for shoreline protection projects and $4,325 for sediment trapping projects. These requirements have constrained the development of monitoring plans for CWPPRA projects to below ideal levels which are more realistically reflected in the cost estimates of Steyer and Stewart (1992).

Monitoring of plan implementation will be undertaken by an independent Third Party who will prepare semi-annual reports describing actions of the BTMC and implementing agencies in relation to shoreline stabilization, induced sediment deposition and sediment trapping projects. Evaluation of monitoring reports concerning project effectiveness will be conducted by qualified individuals representing organizations independent of any agencies or institutions funding the project construction, operation and/or maintenance. Semi-annual reports will be prepared. The monitoring reports will be submitted not less than 15 days prior to a regularly scheduled meeting of the BTMC and the parties responsible for monitoring will appear at the meeting to discuss the report. Monitoring reports concerning project effectiveness will also be provided to the agencies or institutions funding project construction, operation, and/or maintenance, as well as landowners for the project and references areas (as appropriate).

The Quality Assurance Plan involves the following components:

Project Description - (as provided in Action Plan).

Project Organization and Responsibility - (to be prepared by monitor in association with lead implementor).

Data Quality Objectives - For the measurable parameters recommended in this monitoring strategy, Table EM6-xxx3 presents these objectives as determined by Steyer et al. (1995).

Table EM6-xxx3. Data Quality Objectives for identified measurable parameters (after Steyer et al., 1995).

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