A federal program encourages private restoration efforts by allowing companies to exchange mitigation credits.

By Lee Phillips, J. Erik Alford,
and Brad McLeod

Historical urban growth and development has adversely affected the water quality, stability, and biotic integrity of the streams within the city of Griffin, GA. Implementing corrective measures for addressing stormwater runoff is an integral part of the city’s stormwater management program. The program’s objective calls for improving the water quality and biological function of the watershed by incorporating structural and nonstructural best management practices (BMPs). The Stream Restoration Program uses structural BMPs, physically restoring and enhancing features within the watershed to complete the water-quality improvement process.

Griffin’s Stormwater Management Program

Griffin’s population is around 25,000, situated within approximately 15.5 mi.² The city’s watersheds comprise six drainage basins and 39 sub-basins, totaling 16,403 ac. The 157-year-old city has more than 10,000 drainage structures associated with 165 mi. of road inventoried and recorded in the city’s geographic information system (GIS) database. The city is responsible for the operation and maintenance of the entire drainage system, most of which is undersized and requires maintenance.

In 1997, Griffin established a formal stormwater management program (SWMP) and a stormwater department. The city created a stormwater utility, the first in the state of Georgia, to fund this new department. The purposes of the SWMP include managing the watersheds, creating an example for other cities to consider when evaluating possible management models to achieve compliance with the upcoming National Pollutant Discharge Elimination System (NPDES) Phase II permitting process, and addressing total maximum daily loads (TMDLs) for impaired or threatened water bodies within the city. The stormwater utility provides the city with a financial mechanism from which to address both water-quality and water-quantity control issues required as part of the Phase II permitting process. It allows the city to develop BMPs to address nonpoint-source pollution and flood-control management (via infrastructure improvements) that, when implemented together, will ensure protection of water resources within the region.

Griffin’s SWMP acts as a roadmap to guide the stormwater utility and to track the progress of developing BMPs. Currently the city focuses on addressing existing water-quantity and -quality issues on a watershed or basin approach. Specific elements of this focus include hydraulic and hydrologic modeling and subsequent watershed assessments within each basin. The city is also developing a comprehensive land-use plan to prepare for future growth. Figure 1 presents the ongoing work and future goals of the SWMP.

Stream Restoration Program

In addition to its focus on water-quality regulations, the SWMP’s ultimate goal is to restore and protect the streams and associated streambanks, wetlands, and buffers degraded over the years from inadequate stormwater management. Streambank restoration is the act of restoring natural conditions of a degraded stream channel, including stabilizing the stream and streambank and planting native trees, shrubs, and grasses. Measurable results of restoration include reduced erosion and flooding, reestablished buffers, improved water quality and habitat, and enhanced stream aesthetics.

Similar programs examined source control of nonpoint-source pollution, and the thrust of all these programs is to eliminate pollution before it enters receiving waters. Unfortunately, no measure will ever completely eliminate all pollution to the streams. In addition, many of the streams that receive this "polished" stormwater runoff are already in a state of extreme degradation. The City of Griffin believes that healthy streams can finish the job that source controls begin and provide for even healthier waters downstream. When streams are restored to a pristine condition, the natural riparian vegetation within the stream corridor can effectively mitigate minor inputs of pollution that escape upland controls. The steps outlined in Figure 1 will help achieve the goals of NPDES and the TMDL program by providing an end product of healthy streams and rivers in areas of extreme development.

Public/Private Partnership

Stream mitigation and restoration can be especially expensive because of the required ecological and engineering studies and designs, and because of construction costs. The Army Corps of Engineers (ACE) and other natural resource agencies recently estimated that construction costs alone for stream mitigation average approximately $125/lin. ft.; this cost estimate does not include design, coordination, or property acquisition. To address the important issue of project cost, Griffin explored a joint venture relationship, outlined below, to assist with the project.

Alternative Funding. To provide the financial resources for streambank mitigation, the city partnered with a private-sector company to conduct the restoration project. The vehicle for this joint relationship is the ACE Stream Mitigation Bank program, based on the Wetland Mitigation Banks, more than 150 of which have been established nationwide since the Federal Mitigation Banking Guidance was issued in 1995. The Stream Mitigation Bank program allows private organizations to restore degraded streams to more natural conditions in return for the right to sell mitigation credits to other developers who need to impact streams to complete certain aspects of their projects (for example, road crossings or piping projects). Through this program, Griffin can restore its streams at no cost, and the private-sector company can fund the restoration work and even realize a financial profit through the sale of stream mitigation credits.

Developing a Mitigation Bank Prospectus. After Griffin established the public/private agreement, the next step called for developing the concept with a formally binding commitment from each party. A detailed evaluation of the city’s stream and drainage systems was necessary to inventory current problems within the watershed and to identify potential mitigation opportunities. This review provided data to develop a mitigation-banking prospectus, which must be reviewed by a team of natural resource regulatory agencies referred to as a Mitigation Bank Review Team (MBRT). The MBRT consists of representatives from EPA, ACE, US Fish and Wildlife Service, and, in this case, the Georgia Environmental Protection Division.

Developing a Mitigation-Banking Instrument. The private partner is responsible for the design, regulatory coordination, and construction of the stream improvements. Additionally, the private partner arranges with the regulatory agencies to have a mitigation-banking instrument developed to provide a certain number of mitigation credits based on the quality and quantity of improvements conducted within the watershed. The private partner can then sell credits to applicants who needed compensatory mitigation for permits under Section 404 of the Clean Water Act. The city’s responsibilities involve committing its stream segments for evaluation and restoration and placing a conservation easement on the restored stream segments.

Conservation Easements. To prevent future development from affecting rehabilitated areas, Griffin must hold a conservation easement on all lands involved in the restoration effort. Although initial efforts primarily focus on public property owned by the city, private property can be incorporated into the program with the understanding that the restored areas are restricted from future development and must be placed in a conservation easement. A proactive educational approach helps private landowners understand how restoration enhances the community and their own property values. The city can prepare the easements to allow for future trail systems and other desired projects that have minimal impacts on the restorations and provide non-automotive access throughout the city, allowing many passive and active recreational uses of these natural settings.

Phase I: Stream Investigation and Characterization

The program has been structured with a phased approach. Phase I included stream investigations and characterizations to develop the stream mitigation prospectus. During the Phase I stream investigation, all streams within the city were assessed for inclusion in the project. Primary stretches for consideration included systems on city-owned property; secondary stretches consisted of systems located on private property. The emphasis rested on locating degraded stream segments in the upper reaches of the watershed. During the initial investigation, all streams within the city were generally classified based on actions needed:

• Restoration. Highly degraded, acceptable for full streambed and streambank restoration
• Restoration or Enhancement. Moderately degraded, acceptable for restoration of streambank or streambed
• Enhancement. Slightly degraded, acceptable for enhancement of aquatic habitat
• Preservation. Intact streambed or riparian corridor acceptable for permanent preservation

Many streams and associated riparian corridors within the city received a classification of "highly degraded," having been channelized and severely entrenched by high-velocity runoff. Streambank undercutting and collapses are common through many of the reaches reviewed.

A total of 84,514 lin. ft. (16 mi.) of streams within the city limits have been visually assessed and placed in a preliminary category for enhancement, restoration, or preservation and are incorporated into the city’s GIS database. Restoring streams and riparian corridors is most effective if the restoration project includes the full reach of a stream rather than being interrupted by sections of degraded reaches. Because not all sections in need of restoration lie on city property, careful public coordination will likely be required.

Figure 2. Project Location Map. Click here for an enlarged view

Figure 2 shows the initial stream segments selected for inclusion in the city’s Stream Restoration Program. These segments were selected based on basin location, degree of degradation, and accessibility.

Phase II: Physical Restoration

Phase II of the project involves the physical restoration of natural features with the watershed and its timely return to a more pristine condition of water quality and a restored biological function. Although restoration could occur through natural processes, the return of many biological functions would require an extended period of time. Physically implementing efforts to restore watershed ecosystems and protecting vegetated buffers will serve as a catalyst to return water quality and biological functions to near pre-impact levels.

Typical restoration activities include planting native trees and shrubs within all wetland and stream restoration areas, as indicated in Tables 1 and 2. All disturbed areas will be vegetated with a native seed mix shown in Table 3. Native vegetation that will thrive within these areas, providing water-quality improvement, enhanced habitat, and shading, has been specified. Several of the shrub species supply berries (winterberry, chokeberry, possum haw, and so on) that will attract and provide forage for neotropical birds.

Table 1. Recommended Native Tree Species for Wetland and Stream Restoration

Table 2. Recommended Native Shrub Species for Stream Restoration

Table 3. Recommended Grass Species for all Disturbed Areas

The plant species specified are generally available from local nursery stock, but some native substitutions will be allowed with approval of the project biologist. A detailed planting schedule will be developed after approval of the conceptual restoration plan. Baseline data will be studied to assess the existing vegetation found within each of the reference wetlands and streams. A comprehensive listing of trees, shrubs, and grasses identified within the selected reference areas will be utilized to form the basis for the planting design.

Classification Methodologies

Stream segments in the Potato Creek watershed were selected for restoration: near the Griffin Library (top and center and the Oak Hill Cemetery (bottom).

The Rosgen stream classification method provides a way to categorize streams based on general morphology, slope, and channel-bed materials for comparison with other similar streams. The methodology identifies 41 major stream types for which stream channel stability and streambank erosion potential can be assessed. From the assessment, structures for in-stream and streambank restoration can be selected based on the stream-type category.

The following methods will be used for stream classification to acquire stream reference reach data. Reference reaches are established for each general stream type by locating representative transects between pools and riffles with no obstructions to flow. The locations of transects will be at the narrow width of the transition reach as it extends from a riffle into the head of a pool.

The mapped cross-section of the channel reach will identify specific stream characteristics such as the elevations of the deepest point in the stream channel, bankfull stage, and flood-prone stage. In addition, using surveyed maps with 2-ft. contours and recent aerial photography determines channel and valley slope.

To accurately determine the composition of the streambed material, Wolman method streambed pebble counts are conducted at transect locations based on the ratio of riffles/runs to pools. Calipers measure the intermediate axis of each particle, which is then classified into the Wentworth size classes. The cumulative percent composition is graphed, and the d50 (median diameter) is used as the mean bed material.

The Pfankuch channel stability index helps to evaluate channel stability. The method includes 15 categories evaluated for one of four levels of stability (excellent, good, fair, or poor). Each level corresponds to a numeric index value; values for the categories are summed, and the total corresponds to a Pfankuch rating of good, fair, or poor.

Rosgen’s bank-erodibility hazard rating guide assists with the evaluation of bank erosion potential. The guide incorporates an index value for ratio of bank height to bankfull height, ratio of root depth to bank height, root density, bank angle, surface protection, bank materials, and stratification. After index values are summarized, an erosion potential rating is assessed.

Using the data from the above-mentioned methods helps to determine a stream type. In-stream and streambank structures that are best suited for restoring that stream type are chosen based on Rosgen’s recommendations (Rosgen, 1996).

The same research methodology used on the impaired stream reach will be implemented within a reference reach within the nearby area. This reference reach will allow for accurate conclusions as to the type and condition of stream to which the impaired stream will be restored.

With the stream classification system, stream design will be undertaken to allow for suitable structures to be installed while maintaining the project goals of improving in-stream habitat conditions for aquatic biota and preventing further erosion of the stream channel.

Stream Restoration Monitoring

The projects must be monitored for success twice annually for up to seven years to evaluate the effectiveness of the restoration effort in reestablishing natural/estimated water quality and biological conditions. A stream restoration monitoring plan is used to evaluate the construction and installation of structural and vegetative components of the restoration and the stability of the measures after installation, assess aquatic wildlife, and evaluate water chemistry and survival of planted herbaceous and woody vegetation. This monitoring plan, based on the Rosgen method, uses qualitative measures to evaluate the structural, wildlife, and herbaceous components and quantitative measurements for aquatic biota and woody vegetation survival.

Routine inspections of the restoration site will be conducted during construction to evaluate streambank stabilization, planting methods, condition of planted material, erosion control measures, compliance with design plans, and progress. These inspections are qualitative in nature, commenting on the condition and progress of the restoration. Additionally, comprehensive inspections will be conducted on a quarterly basis for the first year and twice annually for the next four years following construction to accurately evaluate the effectiveness of the stream restoration projects. The purpose of the inspections is to project stabilization practices and to evaluate erosion, bank failure, bare areas, bank sloughing, undermining, rill formation, settling, percent vegetation establishment, material integrity, sediment deposition, and maintenance needs. The stability and effectiveness of the restorations will be evaluated under low- and high-flow conditions. At least one inspection during and after high-flow conditions will be conducted. Overall structural conditions will be evaluated and included in the monitoring report.

Streambank vegetative protection monitoring will measure the amount of vegetative protection provided to the streambank and the near-stream portion of the riparian zone. This parameter provides information as to the bank’s ability to resist erosion as well as control stream scouring and shading within the stream.

Aquatic Biota Monitoring. Reference reach stations will be monitored for benthic macroinvertebrates as well as fish species. To assess the effectiveness of habitat structures, richness, diversity, and trophic assemblage, composition will be evaluated annually for five years for both fish and benthic invertebrates. Baseline samples of these indicators were collected as part of the city’s watershed assessments. These parameters provide a description of the aquatic community based on the number of species present (richness), the abundance of individuals within each species (diversity), and their relationship in the stream continuum concept (trophic assemblage) and also provide insight into the ecological stability and health of the stream ecosystem. The parameters are also common in several biotic indices, including EPA’s 1999 Rapid Bioassessment Protocol for Use in Wadeable Streams and Rivers. Methods used to acquire a representative sample of the aquatic population include the use of electrofishing, kick seining, and dip net samples. If a reference stream can be located within the watershed, equivalent samples will be collected for restoration success comparison.

Water-Quality/Chemistry Monitoring. As a part of the stream restoration project, standard water quality and chemistry will be monitored during wet and dry periods twice annually for five years to evaluate the effectiveness of the restoration effort in reestablishing natural/estimated predisturbance water-quality conditions. Dry samples will be collected only after a 72-hour period or greater of no precipitation greater than 0.1 in. Wet samples will be collected within 24 hours of a precipitation event of greater than 0.1 in. within a 24-hour period. Parameters to be measured include temperature, dissolved oxygen, pH, turbidity, conductivity, nitrates, nitrites, total phosphorus, total dissolved solids, total suspended solids, chemical oxygen demand, biological oxygen demand, fecal coliform, total copper, total lead, and total zinc. Results will be used to evaluate the components of the water column that support aquatic fauna and flora, to determine limiting factor nutrients, and to evaluate the pollutants and indicators of pollution commonly recorded in metropolitan Atlanta-area streams. Baseline water-quality samples have been acquired to determine the background concentration of pollutants in the stream and will be used to measure the success of the restoration efforts. For comparison, samples will be collected from a reference stream located within the watershed.

Stream Reclassification

At years three and five, a reevaluation of the stream classification in accordance with Rosgen methods will be conducted at the initial classification transects. In areas requiring corrective measures, the evaluations will be conducted at three and five years from the time of the installation. Photographic documentation will be conducted from permanent stations during each site visit to record wildlife use of the sites based on coverage of the restored habitats, inclusion of structural components, and aesthetic evolution.

Success Criteria

Project success or failure for the restored sites would be determined following the fifth year of monitoring. A successful project should consist of the following components:

• Pollutant removal as the restored stream returns to a natural state.
• A final survival rate of 70% of all planted vegetation. Final plantings per acre will be determined in prerestoration field studies of average densities of the forested wetland systems within the project area.
• Proven periods of extended surface and subsurface hydrology measured monthly in shallow water wells for wetland restoration areas.
• Hydrophytic ground cover and recruited woody community developed because of increased hydrology for wetland restoration areas. Determination that the herbaceous community is hydrophytic will be based on the prevalence index rating. The herbaceous community should have an index below three to be successful.
• Wildlife use of mitigation areas.

Annual reports for a period of five years will be generated for the Forest Renewal Management Branch. These reports will include information such as condition of streams, surface and groundwater levels, survival rate of planted species, natural recruitment of species, and natural development of a ground cover stratum in respect to hydrological periods.

Summary

Through the Stream Restoration Program, the City of Griffin has the potential to delist streams that are currently on the state’s 303(d) list, as well as to develop a model approach for other local jurisdictions as water-quality continues to move to the forefront of growth and development issues. Additionally, the city can benefit from enhanced storage capacity in the floodplain as the vegetation planted as part of the restoration matures and protects streambanks and riparian habitats. The Stream Restoration Program will also prove to be a vital tool in meeting the requirements of regulatory programs such as NPDES Phase II, the TMDL program, and the Source Water Protection Plan. Griffin will also be a step ahead of potential required improvements and protections associated with expansion of facilities (for example, water reclamation discharge permits and associated watershed assessment studies) that require the approval of the Georgia Environmental Protection Division.

Furthermore, mitigation has long been a desperate need for many development projects. The need will become even greater with the recent changes in the ACE’s nationwide permits for working within wetlands and streams. Most impacts to open waters (streams, rivers, and so on) will now require compensatory mitigation in an effort to achieve no net loss of function or acreage of streams and wetlands. Furthermore, most impacts that exceed 0.1 ac. of any wetland will now require mitigation. Though historically mitigation banks were a desirable option, these regulatory changes will make the option of purchasing credits from a bank even more desirable.

The MBRT, with its representatives from several agencies, also provides a platform for the city to initiate a partnership with the natural resource regulatory agencies to gain their understanding and support of initiatives to improve water quality. This opportunity will help in developing the contacts and support needed for Griffin to continue to establish a model for other urban areas to follow.

Reference

Rosgen, D. Applied River Morphology. Wildland Hydrology, Pagosa, CO. 1996.

Lee Phillips is a project manager within the Water Resources division of Integrated Science & Engineering Inc., the stormwater consultant for the Griffin Stormwater Department. J. Erik Alford is president and Brad McLeod is a senior ecologist with Ecological Solutions Inc., the natural resources subconsultant for the Griffin Stream Restoration Program.

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