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St. Croix East End Watershed Restoration Project

St. Croix East End Marine Park watersheds map.In September 2011, through the Conservation Technical Assistance Program (CTAP), NRCS awarded a grant to the St. Croix Environmental Association (SEA) to complete engineering designs and plans for two priority restoration projects identified in the St. Croix East End Marine Park (STXEEMP) watershed management plan. CTAP provides conservation technical assistance to landowners and nonprofits to apply best management practices on private land to conserve and improve natural resources. CTAP assistance includes habitat protection, restoration, development or enhancement for upland wildlife, wetland wildlife, threatened and endangered species, fisheries, and other types of wildlife.

In 2014, NRCS partnered with the NOAA Restoration Center and NOAA Coral Reef Conservation Program (CRCP), DPNR Coastal Zone Management Program, SEA, Horsley Witten Group, Inc., the National Fish & Wildlife Foundation (NFWF), Geographic Consulting, LLC, and Green Cay Farm LLP property owners to install conservation practices in one of the priority sites.

BackgroundEndangered Acropora corals.

Coral reef ecosystems in the USVI and Wider Caribbean Area are threatened by many natural and man-made stressors, but the primary threat to our coral reefs is sediment.  Most developments lack properly designed and installed storm water drainage systems, and many are accessed by unpaved road networks.  These unpaved road systems are both sediment sources and sediment delivery systems, routing sediment-laden runoff directly to sensitive coastal areas.

Sediment (and bacteria) impairs water quality in many bays in the St. Croix East End Marine Park (STXEEMP).  These pollutants harm the ecological health, recreational use, and commercial resources of the STXEEMP. As a result, coastal managers identified the St. Croix East End watersheds as priority areas for pollution prevention and restoration work.

Southgate Coastal Preserve and Chenay Bay, St. Croix, USVI.Project Sites

Southgate Watershed

The Southgate Watershed is a mixed use watershed that contains Southgate Pond, one of the largest salt ponds in the USVI and an ecologically-significant habitat. Development in the watershed has increased paved surface area, altered water flow patterns, and decreased groundwater recharge. These dramatic increases in storm water runoff have caused severe erosion of gut (intermittent stream) banks in the watershed.

St. Croix Field Office staff visit severely eroded section of Southgate watershed's East Gut, located on Green Cay Farm, January 2007.East Gut flows east to west and drains into Chenay Bay, which is impaired for turbidity. Over the years, the gut became severely eroded – this type of erosion is called a head cut. The head cut in East Gut caused sheer, unstable walls, a widening stream channel and severe soil erosion. The head cut was about 20-40 feet wide and 10-15 feet deep, and had three main lobes. The most eroded section of the gut was about 1,500 feet long and full of debris (cars, appliances, roofing tin, etc.) – remnants of past unsuccessful attempts to slow bank erosion. Sediment from the eroded gut was observed downstream; and sediment-laden water from the gut discharged into Chenay Bay, listed as impaired for turbidity by the V.I. Department of Planning and Natural Resources in 2010.

  • Objective: Design complete engineering plans & drawings to stabilize the eroding gut.
  • Goals:
    • Protect mangrove wetlands and salt pond habitats for wildlife [protected Bahama ducks (Anas bahamensis), piping plovers (Charadrius melodus), brown pelicans (Pelecanus occidentalis), pied-billed grebes (Podilymbus podiceps), and Caribbean coots (Fulica caribaea)];
    • Reduce sediment loads to Chenay Bay and STXEEMP; and
    • Protect coral reef habitat for endangered elkhorn and staghorn corals (Acropora sp.), juvenile spiny lobster (panulirus argus), and nesting habitat for threatened and endangered hawksbill and green sea turtles (Eretmochelys imbricate and Chelonia mydas).
Solitude WatershedRoad erosion in Hope and Carton Hill leading to sedimentation of Solitude Bay.

The Hope and Carton Hill/ Yellow Cliffs residential area lies in the upper reaches of the Solitude watershed. These neighborhoods have almost 5 miles of very steep, mountainous, and unpaved roads. The roads have many deep ruts and gullies that erode and carry storm water and large amounts of sediment during rain storms. All of this runoff and sediment ultimately wash into the main gut of the watershed; carrying an estimated 112 tons of sediment per year – 11 times higher than under natural conditions – into the marine habitats of Solitude Bay and the STXEEMP.

  • Objective: Develop a Road Drainage Master Plan to reduce erosion of the steep, dirt road network serving the Hope and Carton Hill neighborhood.
  • Goals:
    • Reduce sediment loads to Solitude Bay and STXEEMP;
    • Protect nesting areas for threatened and endangered hawksbill and green sea turtles (Eretmochelys imbricata and Chelonia mydas); and
    • Protect coral reef habitat for endangered elkhorn and staghorn corals (Acropora species) and juvenile spiny lobster (panulirus argus).

Project Accomplishments

Southgate WatershedPartners visit eroded gully on Adams family pastureland, St. Croix.

SEA contractor, Horsley Witten Group, Inc., completed engineering drawings and designs to stabilize the most severely eroded section of the Adams Family gut in September 2012. HW confirmed the rate of head-cut migration to be approximately 10-15 feet per year, through the use of aerial photography. The solution was to regrade the sides of the gut and then stabilize the soils with large boulder step-pools, erosion control mats and plants. Their design was limited to the emergency repair of the head cut to prevent additional erosion.

The restoration design utilized a combination of “soft” and “hard” stabilization techniques. “Soft” stabilization measures included natural materials like coconut (coir) fiber mats, grasses, and various native shrubs and trees. “Hard” stabilization practices included rip-rap and large boulders (i.e., quarry stones).

Through a NOAA-CRCP grant, Green Cay Farm hired local contractor, Marco St. Croix, to regrade and stabilize the gut. After grading the sides of the gut to shallower slopes, the gut stream bed was lined with boulders to slow the speed of the water and break up its energy. The boulders were shaped into step pools where each pool fills with water and then spills into the next (see below). Property owners also received EQIP assistance to  install a stream crossing and fencing to restrict livestock access to the stabilized channel.

 

Geographic Consulting propagated native plants in their tree nursery for the project. They installed the plants on the newly-formed slopes by cutting holes in the erosion control mats (below). The plants will stabilize the banks long after the fabric decomposes. Native plants are best adapted to St. Croix East End conditions and will provide wildlife habitat as they mature.

 

Severely eroded Green Cay Farm East gut before stabilization; During stabilization: large stones placed to create step pools to slow water; After: final planting with native trees.
Left: Severely eroded Green Cay Farm East gut before stabilization; Center: During stabilization large stones were placed to create step pools to slow water; Right: coir mats installed after stabilization and final planting with native trees and grasses.
 
Solitude Watershed

Hope & Carton Hill HOA Meeting to discuss draft Road management plan.SEA contractor, Horsley Witten Group, Inc. (HW), also completed a Master Drainage Plan for the Hope and Carton road network in January 2013, and designed and installed a demonstration rain garden in the neighborhood.

In October 2012, the project partners, together with Hope & Carton Hill residents, installed the first demonstration rain garden in the watershed. SEA, HW and NRCS staff worked with homeowners, contractors, and volunteers to excavate and shape the rain garden, donate & deliver mulch and compost, and plant over 50 native or naturalized species purchased locally or donated by partners and residents. The rain garden got its first test a few weeks later, handling ~2 inches of rainfall.

HW & NRCS staff also held several meetings with over 16 neighborhood residents to gather information about problem areas in the watershed, solicit input to the Road Management Plan, and present the draft Drainage Plan and gather input and recommendations to improve the plan.

DocumentsHope & Carton Hill rain garden 7 months after installation.

For More Information

Please contact the St. Croix Field Office at 340-692-9632 x3.