A Simple, Low-Cost Technique to Retrofit Riprap Shorelines

Green Your Riprap: A Simple, Low-Cost Technique to Retrofit Riprap Shorelines

This guide is for river restoration experts and homeowners who want to improve the ecological and aesthetic value of shorelines armored with riprap revetments. In 2013 and 2015, U.S. Fish and Wildlife’s Chesapeake Bay Field Office experimented with a technique, Green Riprap, to establish marsh plants in the spaces between rocks in existing revetments along tidal shorelines. Projects were completed on the Severn and Magothy Rivers near Annapolis, MD.

Shoreline Hardening in the What is Green Riprap? Chesapeake Bay Green riprap is a small-scale, low-cost restoration technique for improving existing riprap shorelines, Over 18% of the Chesapeake Bay has been and involves planting riprap with tidal marsh hardened, in many cases through riprap plants. revetments. When a tidal shoreline is hardened, fringe marsh ecological benefits disappear. Revetments do not filter out nutrients and capture sediment, so these enter the Bay instead. Organisms can no longer find food, shelter, or refuge in the intertidal area. The terrestrial and aquatic communities that are able to use riprap Benefits of Green Riprap for habitat are different than those in fringe tidal marshes. Without marsh vegetation to shade the  Habitat, food, and refuge for aquatic and shoreline, nearshore water temperatures terrestrial life increase, harming the ability of aquatic organisms  Shade to cool nearshore water temperatures to utilize the area. Replacement of fringe marsh  Filtration of nitrogen and phosphorus areas with riprap has serious consequences for the ecology of shorelines.  Sediment capture If a landowner wants a simple and low cost  Absorption of wave energy and reduction of way to improve the ecological and scour aesthetic value of their existing riprap  Aesthetic improvement of property shoreline, Green Riprap is a viable option!

1 Success Story: Round Bay Community Beach

BEFORE 4 YEARS LATER

Site Conditions Unique Features: breakwater present Wave energy: Fetch of 2 mi to the SSW. Significant boat wake Nearshore water: Some of area has exposed beach off the rock, other areas have gently sloping shallow water not exposed at normal low tide Sediment: Less than 1” of sediment accreted. Aspect and Shade: South facing. Full sun. Existing plants: none Immediately after planting, 2013 The community of Round Bay wanted to beautify and improve the riprap that was present along their community beach. With the help of the Chesa- peake Bay Field Office of USFWS, they planted 600 marsh grasses along 300 feet of bare riprap shore- line. Planting was done by wedging the grass plugs (grown out in 3” coir pots) between the rocks. An existing breakwater likely helped the grasses es- tablish and spread further along the riprap by miti- gating 2 miles of fetch and significant boat wake. Community members were so pleased with the success of the planting that they have since planted more grasses on their beach. Landowners along the beach are especially satisfied with the aesthetic improvement upon the bare rock.

2 Success Story: West Severna Park Marina

BEFORE

5 YEARS LATER

Site Conditions Wave energy: Max fetch of 0.3 miles to the SSW. Protected cove, no boat wake Nearshore water: Bottom is not exposed at normal low tide Sediment: Less than 1” of silty sediment accretion in rock. Aspect and Shade: South facing. Full sun. Existing plants: High tide bush, Hibiscus Immediately after planting, 2013 3 Planting Tips

Figure 1. Planting zones on rip rap shorelines.

Grow plugs in 3” round coconut fiber coir pots for approximately 4-6 weeks to establish a robust root system. Plant grasses by moving the rocks and wedging the plants in the voids of the rip rap. Successful wedging will ensure that the plants do not wash away with the tides. Ensure that the grasses are planted in the correct hydrologic zones (see Figure 1). Remember that the plant roots will be at a lower elevation compared to the rock surface. Use other marsh plants growing nearby to locate the mid– and high-tide lines. Planting should occur at low tide for ease of access. Because planting in rocks can be difficult, it may be helpful to stand in the water or kneel on a foam pad on the rocks.

Learn more about the ecology of hardened shorelines

Dugan, J. E. et al. (2011). Estuarine and coastal structures: environmental effects, a focus on shore and nearshore structures. Treatise on estuarine and coastal science, 8, 17 -41.

Fischenich, J. C. (2003). Effects of riprap on riverine and riparian ecosystems (No. ERDC/EL-TR-03-4). Engineer Research and Development Center—Vicksburg MS Environmental Lab.

NOAA. (2017). Impacts of Hardened Shorelines on Aquatic Resources: Research Questions? Contact Us! Summary. NOAA National Centers for Coastal Ocean Science. Retrieved from https:// chesapeakebay.noaa.gov/shorelines/shorelines. Leah Franzluebbers [email protected]

Seitz, R. D., et al. (2006). Influence of shallow-water habitats and shoreline (410) 173-4181 development on abundance, biomass, and diversity of benthic prey and predators in Rich Mason Chesapeake Bay. Marine Ecology Progress Series, 326, 11-27. [email protected] (410) 173-4184 4