California Coastal Commission




I. Introduction:

Mitigation for the adverse affects of development projects in wetlands can take on a variety of forms. Compensatory mitigation (enhancement, restoration, or creation) is the most common mitigation proposed in coastal development permit applications. However, under certain circumstances the CCC has also accepted less desirable mitigation alternatives such as in-lieu fees and contributions to mitigation banks. Although a variety of mitigation alternatives exist, all of them have drawbacks and limitations. (Not the least of which is the large amount of money often required to undertake a mitigation program.) Numerous partially successful, or failed mitigation projects attest to the fact that mitigation is not a panacea. Past experience clearly shows a great deal of effort is required by all parties to ensure successful mitigation.

This chapter presents a brief overview of several common mitigation alternatives for proposed projects directly affecting wetlands. Additionally, the chapter presents information on mitigation ratios, and more detailed information on restoration plans.

II. Mitigation Defined:

Although the Coastal Act does not define mitigation, the California Environmental Quality Act does. Under CEQA, mitigation includes all of the following:

a) Avoiding the impact altogether by not taking a certain action or parts of an action.

b) Minimizing impact by limiting the degree or magnitude of the action and its implementation.

c) Rectifying the impact by repairing, rehabilitating, or restoring the impacted environment.

d) Reducing or eliminating the impact over time by preservation and maintenance operations during the life of the action.

e) Compensating for the impact by replacing or providing substitute resources or environments.

This definition is hierarchical with avoidance being the most preferred type of mitigation and compensation being the least preferred type.

Past experience in reviewing applications for coastal development permits shows applicants rely heavily on compensatory mitigation to minimize habitat loss, regardless of the impacts. Typically, compensation measures are included as an integral part of the project design. This form of mitigation is often justified through arguments designed to show that the wetland acreage enhanced or restored is equal to the acreage lost. However, this concept of compensatory mitigation often fails to recognize the complexity of the wetland ecosystem, its relationship to the watershed, and the fact that wetland functions may not be directly related to acreage. Additionally, the success of compensatory mitigation — especially restoration projects — is not proven. Overall, more emphasis should be placed on mitigation alternatives that include wetland impact avoidance and minimization. Compensation for wetland impacts should only be considered as the last alternative, and only if there are no other less environmentally damaging feasible alternatives.

III. Types of Mitigation:

A) Avoidance:

Avoidance of project impacts is the preferred mitigation alternative under CEQA. Through this form of mitigation, adverse impacts are avoided altogether through alteration of project location, design, or other related aspects. For obvious reasons, this mitigation alternative is not generally preferred by permit applicants, since it requires a change (possible substantial) in the proposed project. Yet in evaluating mitigation alternatives, CCC staff should give first consideration to impact avoidance for all or some of the proposed project impacts.

B) Enhancement, Restoration, and Creation:

The enhancement, restoration, or creation of wetlands are three types of compensatory mitigation. In this document, enhancement is considered a mitigation activity that improves the size or function of degraded or other existing wetlands. Restoration is considered a mitigation activity that re-establishes a former wetland. Creation is considered a mitigation activity that results in the formation of a new wetland.

Although not without drawbacks, enhancement of an existing wetland is among the most common type of compensatory mitigation. The principal shortcoming of most proposed enhancement projects is that they can often result in a net loss of wetland acreage (Table 1). Only through the restoration of former wetlands or through the creation of new wetlands can no-net-loss be achieved. Enhancing existing (e.g., degraded) wetlands as mitigation for wetland resources does not provide additional wetland acreage, but can increase the function and value of existing habitat.


Type of Mitigation



Enhancement of degraded wetlands with some existing functional value.

Good chances of success, since project located in an existing wetland ecosystem.

Net loss of wetland area and/or functions.

Restoration of former wetlands area with no present functional value.

Net gain of wetland acreage and function. Success rate higher than for projects creating new wetlands.

Still somewhat experimental. May be a long time between loss of developed wetland and completion of the restoration project.

Creation of a new wetland site not adjacent to existing wetland.

Provides greater flexibility for mitigating impacts.

Still experimental. Success rate is low. Functional value not well documented.

CCC staff should review wetland enhancement projects carefully. All wetlands in coastal California are extremely valuable, even if degraded, because of the dramatic loss in wetlands throughout the State, and the unique habitats wetlands provide. In urban areas, the remaining wetlands still support important plant and animal species. Though many of these wetlands are disturbed by human activities, they can still be a significant resource.

In contrast to enhancement projects, the restoration of a former wetland can result in a net increase in both wetland acreage and function (Table 1). Restoration of a former wetland is by no means foolproof, but may have a reasonable chance of re-establishing fundamental wetland characteristics such as the proper elevation or hydrology. However, having no guarantee the restoration project will achieve the stated goals in the specified time frame is a major concern regarding wetland restoration. To provide a higher probability of success, the restoration project should be located adjacent to a functioning wetland. Isolated restoration sites will probably have a lower chance of sustaining maximum function and values, due to isolation from seed sources, and limitations on the migration and dispersion of wetland animals. Established connections among wetlands can be critically important in the event of local catastrophes, which can result in localized extinction without inputs from other wetlands.

The creation of a new wetland is probably the most uncertain type of compensatory mitigation (Table 1). Not only must the project provide the proper form and balance of fundamental characteristics, but it must also result in a system that is self-sustaining or provide for a permanent maintenance program. Creating new wetlands has many of the problems associated with wetland enhancement and restoration projects. Additionally, it can be a very long time from the creation of a new wetland to the establishment of functions and values equal to those lost through development. Thus, there is an interim (often permanent) loss of functions and values. CCC staff should be very cautious in recommending wetland creation projects as mitigation for the loss of existing wetlands.

C) In-Lieu Fees and Wetland Mitigation Banks:

In-lieu fees and wetland mitigation banks are two types of compensatory mitigation that result in the applicant allocating funds for the augmentation of wetlands. Typically, in-lieu fees are funds placed in one or more accounts designated for restoration, enhancement, or preservation of existing wetland resources. In contrast, wetland mitigation banks are either existing or newly created wetland areas that are available for purchase and subsequent management and preservation. In practice, funds paid by the applicant are used to purchase a portion (i.e., credits) of an existing wetland mitigation bank, or are used to fund the creation of a new bank. Using a pre-negotiated formula, the applicant draws on the purchased credits to mitigate for wetland impacts arising from the development project.

In-lieu fees and mitigation bank purchases have generally met with limited success in serving as adequate mitigation for wetland losses. As previously discussed, there are numerous technical difficulties inherent to wetland creation and restoration. Additionally, the allocation of funds through these alternatives are generally not tied to a specific type of mitigation. Thus, there is a reduced chance for in-kind mitigation, and even less chance the mitigation site will be near the impact site. Project time lags can also reduce the overall success of mitigation due to the loss of wetland functions between the time of adverse impacts, the collection of adequate funds to undertake the project, and completion of the mitigation project. Resource management agencies have also found that the complete cost of mitigation is not always accounted for in the fees collected, while mitigation bank funds are not always adequate to implement the bank project in a timely fashion. Wetland restoration costs remain high —particularly the purchase of coastal property— especially in southern California, where land is extremely expensive.

Mitigation banks raise special problems of their own. More often than not, the promised mitigation is never realized. Simply put, resource scientists do not know how to build sustainable wetlands that match the functions and productivity of natural wetlands. Thus, any broad use of mitigation banks could lead to a net loss of wetland habitat. Moreover, resource agencies are concerned that the creation of mitigation banks will reduce the barriers to filling wetlands and estuaries, and may even encourage projects, as bank sponsors seek to recover their costs. On a broader scale, there is strong interest at many levels of government in formalizing the mitigation bank process and expanding its use as a viable mitigation alternative for wetland impacts. Nevertheless, it is recommended that CCC staff coordinate with resource agencies to determine the success of a mitigation bank's activities prior to recommending an applicant's involvement in the bank as mitigation for wetland development impacts.

In-lieu fees or contributions to wetland mitigation banks should not be used because the applicant is having difficulty in locating a suitable mitigation site. Often this approach only transfers the problem of locating an appropriate mitigation site to a public agency. CCC staff are encouraged to work with the applicant to reach an environmentally acceptable decision regarding mitigation prior to initiation of the project.

In evaluating various mitigation options, CCC staff should remember that mitigation banks and in-lieu fees are alternatives not solutions. Mitigation banks and in-lieu fees are forms of compensatory mitigation, which under CEQA is the least preferred alternative.

IV. Mitigation Ratios:

When an applicant proposes to restore or create a wetland as mitigation for impacts from development, the CCC must determine if the quantity and quality of the proposed mitigation will adequately compensate for the wetland area lost through development. Resource and regulatory agencies have usually required additional acreage beyond that lost through development, because of interim losses in wetland acreage and functional capacity, and because the success and resulting value of compensatory mitigation projects are uncertain. The ratio of wetland acreage created or restored to the wetland acreage lost to development is termed the wetland replacement ratio or mitigation ratio. Wetland replacement ratios may vary depending on the acreage, functions, and values of the wetland lost to development and the type of mitigation proposed.

To refine and standardize the process of determining mitigation ratios, some agencies have relied on technically based habitat evaluation methods such as the Habitat Evaluation Procedure (HEP) and the Wetland Evaluation Technique (WET). These procedures are complex and include evaluation criteria that are both objective and subjective. Unfortunately, several of the evaluation criteria do not accurately account for the ecological processes present in California's coastal wetlands and this is a major difficulty with the use of HEP and WET in California (Onuf and Quammen, 1985). In an attempt to address this problem a modified version of HEP was developed for use in evaluating California's coastal wetlands. However, this modified HEP has been characterized as even more subjective than the original procedure. Additionally, the use of these methods can result in erroneous information under certain situations. For example, through these techniques it is possible to conclude that a smaller wetland restored to a higher value offsets the loss of a larger wetland with lower values (e.g., a degraded wetland). Finally, a full evaluation under HEP or WET is very involved requiring a great deal of biological, physical, and chemical information. Unfortunately, the required information is often incomplete or nonexistent for many of California's coastal wetlands, rendering completion of these procedures unrealistic.

Because of the controversy and inherent problems associated with HEP and WET, CCC staff are discouraged from using information and results from these procedures to determine wetland replacement ratios. The preferred procedure is to use the results from the functional capacity analysis (see chapter one), which provides for the preservation of both wetland acreage and functional capacity, in evaluating the adequacy of compensatory mitigation and mitigation ratios. In determining if functional capacity is maintained, both the adverse impacts and the proposed mitigation must be evaluated. In order to maintain functional capacity and wetland acreage, a mitigation plan should at least include the following:

V. Enhancement and Restoration:

A. Effectiveness of Enhancement and Restoration:

Wetland enhancement and restoration projects are among the most common types of wetland mitigation submitted with coastal development permit applications. Wetland enhancement and restoration efforts in California have been criticized because of an overall failure to fulfill the goal of no net loss and a failure to replace lost wetland values. These failures are due to many factors, including a lack of project completion, limited project success, and unclear goals and evaluation criteria. For example, in a review of 58 wetland mitigation projects in the San Francisco Bay area, Eliot (1985) found that very few of the projects achieved the stated goals. Additionally, Maguire (1985) identified the inability to accurately evaluate the effectiveness of restoration projects as a continuing problem because of:

However, a more recent study by Josselyn et al. (1993) found that 13 out of 22 (59%) Coastal Conservancy sponsored wetland restoration projects were effective in meeting initial project goals. This success rate is high compared to results of evaluations focusing on wetland mitigation projects (Josselyn et al., 1990). This higher success rate was expected due to the extensive planning that goes into Conservancy projects, the frequent interaction among various resource and regulatory agencies and the Conservancy, and the funding of project grantees who have a genuine interest in restoring wetlands (Josselyn et al., 1993). While wetland mitigation success remains low, the results of Conservancy sponsored projects suggests the potential exists for increasing the success rate.

B. Designing an Effective Enhancement or Restoration Plan:

The creation of a well designed enhancement or restoration plan is a complex process involving all of the following:

The following is a list of design criteria and standards that should be used by applicants in developing an enhancement or restoration plan15:

1) Maximize the chances for success: If a wetland mitigation plan proposes to enhance a degraded wetland area, then enhancement should ultimately improve the function and values with the least amount of habitat modification. Using enhancement of degraded wetlands as mitigation is discouraged because there is often a net loss of wetland area, especially when the area lost through development is considered. However, incorporating an existing wetland ecosystem (no matter how disturbed) into the mitigation plan can dramatically improve the chances of a successful project over creating new, isolated wetlands. An existing wetland will serve as a reservoir of biota that can colonize restored areas and ensure long-term survival of the wetland. Since most new wetlands are isolated, they will not have this reservoir to draw from, and it will be difficult for the wetland to attain the level of diversity and function of a self-sustaining wetland ecosystem.

2) Maximize wetland size: Mitigation plans should strive to maximize wetland size by choosing sites adjacent to or connected with existing functional wetlands. Such plans must also include provisions for the appropriate habitats (e.g., open water, marshland vegetation, mudflat, etc.) in the proper proportions. Large consolidated areas can offer larger habitats and a greater number of habitats resulting in greater species diversity and population size. However, this criterion should not be interpreted as justification to consolidate remaining wetland acreage into "wetland reservations", which would result in a loss of important adjacent upland habitat and can work against the existence of rare species and habitats.

3) Maintain linkages between wetlands: Where two or more wetland habitats or systems are connected, a mitigation plan should maintain these linkages. Wetland connections should not be severed by development. These connections are vitally important as migration corridors and transition zones between wetlands and adjacent habitats. These connections are also critical for the recolonization of wetlands that suffer local catastrophes such as lagoon closures, or episodes of acute toxicity.

4) Establish and maintain buffer areas: Buffer areas are undeveloped lands surrounding wetlands. These areas act to protect the wetland from the direct effects of nearby disturbance (both acute and chronic), and provide habitat for organisms that spend only a portion of their life in the wetland such as amphibians, reptiles, birds and mammals. (See chapter one for more information on buffers.)

5) Use of existing vegetation and soil: Mitigation projects should strive to salvage the wetland vegetation and topsoil removed during construction for use in the mitigation area. Additional plant material should be drawn from local sources so that local gene pools are maintained. Non-native wetland plants or plants and soils from different regions should not be used at the restoration site.

6) Revegetation: The success of revegetation can be enhanced by planting species at their elevation of greatest natural abundance and in soils with a salinity no higher than those found in the native habitat. In addition, transplanted vegetation may require additional maintenance, such as watering or enclosures to prevent grazing, until they become established.

7) Consider elevation and topography: The elevation and topography of wetland areas is critical to determining the hydrologic regime and the resulting habitats. Elevation changes on the order of centimeters can have dramatic effects on the wetland ecosystem. Not only must the elevations be determined accurately, there must be sufficient detail so that an overall understanding of the landscape topography is clear. For example, intertidal habitat should slope towards the channel at an even grade of one to two percent to reduce ponding and maximize the intertidal area.

8) Consider Hydrology: The source and supply of water to the wetland is key to determining the overall structure of the ecosystem. For wetlands connected to the ocean, the tidal prism must be sufficient to provide adequate exchange of saltwater over the tidal cycle. This is especially important in lagoons where closure of the lagoon mouth may or may not be a natural phenomenon. Designs for new wetlands must incorporate protection from the direct force of waves and tidal currents. Fresh water sources must also be accounted for in the mitigation design. Freshwater supply can vary dramatically throughout the year in many parts of California. The mitigation design should also consider the beneficial flood control function of a wetland.

9) Minimize sedimentation: If excessive sedimentation is a potential problem, then the mitigation plan must include sediment basins and/or maintenance dredging programs to control the build-up of sediments. The plan should encourage the use of upstream sediment controls, including prohibition of grading during the rainy season, stabilization of slopes prior to the rainy season, and protection of native vegetation on steep slopes and stream banks.

10) Construction timing: In order to minimize the disturbance to existing wetland habitat, mitigation projects should avoid active periods of reproduction, growth, or migration of wetland species.

C. Contents of an Enhancement or Restoration Plan:

The following list of criteria is intended to assist applicants in preparing an enhancement or restoration plan, and CCC staff in reviewing such plans. At a minimum, an acceptable plan will include:

1) Clearly stated objectives and goals consistent with regional habitat goals. These regional goals must identify functions and or habitats most in need of enhancement or restoration and must be as specific as possible. If the regional goals have not been identified, then the applicant and CCC staff should work with relevant federal, State, or local agencies to determine if the proposed plan is consistent with the ecology and natural resource composition of the area.

2) Adequate baseline data regarding the biological, physical, and chemical criteria for the mitigation area.

3) Documentation that the project will continue to function as a viable wetland over the long term.

4) Sufficient technical detail in the project design including, at a minimum, an engineered grading plan and water control structures, methods for conserving or stockpiling topsoil, a planting program including removal of exotic species, a list of all species to be planted, sources of seeds and/or plants, timing of planting, plant locations and elevations on the mitigation site base map, and maintenance techniques.

5) Documentation of performance standards, which provide a mechanism for making adjustments to the mitigation site when it is determined through monitoring, or other means that the enhancement or restoration techniques are not working.

6) Documentation of the necessary management and maintenance requirements, and provisions for remediation should the need arise.

7) An implementation plan that demonstrates there is sufficient scientific expertise, supervision, and financial resources to carry out the proposed activities.

8) A monitoring program (see below for more details).

D. Basic Standards for a Monitoring Plan:

A monitoring plan is a critical component of an enhancement or restoration plan that provides an objective way to evaluate the success of the project. When properly conducted, monitoring provides invaluable information regarding:

The monitoring program is intended to document changes in the physical, chemical, and biological status of the mitigation area through the collection and analysis of relevant data. The monitoring plan should include the following components:

1) Provisions for independent monitoring of the site at least five years after completion of the mitigation project. The intent is to continue monitoring until the project has successfully met the stated goals and objectives. For larger projects where new wetlands are created, extended monitoring will be required.

2) Repetitive surveys for plants and animals (including species of special concern) throughout the various habitats of the mitigation area. The surveys should use techniques that permit a determination of species composition and abundance. Both terrestrial and aquatic organisms should be surveyed. Timing of the surveys should be considered, since the abundance of many plant and animal species often varies with season. Surveys sufficient to characterize the mitigation site should also be completed prior to any enhancement or restoration activities.

3) Monitoring of hydrology. For tidal wetlands this would include a determination of the areas inundated at high and low tide, tidal prism, and water velocity. For non-tidal wetlands, this would include determination of permanent and seasonal patterns of inundation and water sources.

4) Monitoring of water quality. Repetitive sampling of various chemical and physical constituents such as salinity, pH, nutrient concentration, dissolved oxygen, temperature, and turbidity throughout the year. The sampling pattern may vary throughout the year and may include more intensive sampling over several tidal cycles to determine short-term salinity patterns.

5) Monitoring of soil chemistry. This will serve primarily to document trends in soil salinity in tidal wetlands, but may include measurements of other constituents as required.

6) Ongoing procedures for the identification and correction of problems as they arise. Such problems may be related to the physical, chemical, or biological attributes of the mitigation site, or difficulties in meeting enhancement or restoration objectives and timelines. These procedures should include specific remedies in case the mitigation project does not meet the designated goals.

7) Provisions for timely analysis and production of annual reports. These reports will be distributed to the CCC and other interested parties. The final monitoring report, submitted upon completion of the monitoring program, should analyze all monitoring data and presents different management options.


14For specific examples see permit numbers 5-90-913, 5-92-408, 5-93-276, 6-86-2, 6-87-611, 6-87-667, 6-88-277, 6-88-388, 6-89-195, 6-90-219, 6-90-77.

15For further information on this subject, the reader should consult other published documents, such as Salt Marsh Restoration (Zedler, 1984), and Marsh Restoration in San Francisco Bay: A Guide to Design and Plan (Josselyn, 1984), and references within.

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