In the USVI, rainfall tends to run down hillsides over the surface rather than through the ground because the soil layer is thin and the underlying rock has low permeability (Jarecki and Walkey 2006). Natural stormwater channels, known as “ghuts”, that have formed from stormwater erosion down steep terrain, are defined as any stream with a reasonable well-defined channel, which includes streams that have a permanent flow as well as those that result from the accumulation of water after rainfall (VIC 12, Ch 3). These channels typically convert to basin sheet flow or drain into a salt pond or bay, and most streams do not maintain a permanent connection to the sea. Beach berms are occasionally breached after persistent heavy rainfall, which establishes temporary connectivity for movement of diadromous species. Some ghut systems are stream-fed, resulting in reliably permanent pools that are connected by stream flow during the rainy season.
Freshwater sources in the northern USVI are extremely limited due to steep topography and lack of flat land for ponding (St. Croix has more freshwater ponds due to more level areas). Water that collects in gut pools provides a rare freshwater habitat that is occupied by freshwater shrimp and anadromous fish. American eels (Anguilla rostrata) are occasionally found in these stream channels (D. Nemeth, pers. comm.). These riparian species have complex life cycles, migrating between downstream marine environment and upstream freshwater pools when connections between the two habitats are present. Bats and migratory birds, primarily warblers, use these ephemeral water resources, as do invasive species that require freshwater, such as the Cuban treefrog (Osteopilus septentrionalis), cane toad (Rhinella marina), and red-eared sliders (Trachemys scripta). Vegetated guts also provide habitat corridors for wildlife, particularly in highly disturbed, urbanized areas. The federally endangered Virgin Islands tree boa (Chilabothrus granti) in particular benefits from these “green belt” corridors along guts on St. Thomas’ east end. The gallery vegetation in guts holds soil to prevent erosion and protects marine and salt pond water quality by filtering sediment and absorbing pollutants from stormwater runoff (Benoit and Nemeth 2011).
Despite statutory protection for gut vegetation (VIC 12 Ch 3), the habitats within these riparian corridors are often highly degraded. Many guts have been altered through habitat clearance, diversion of water flow, and encroachment. Unpermitted vegetation clearance reduces the ability of these systems to withstand erosion, and sedimentation occurs when soil is eroded from the land surface and transported by rainfall moving over ground surfaces. Unpaved roads and the failure to properly install effective silt control devices at construction sites are a major source of eroded soil (Ramos-Scharrón and MacDonald 2005). The sediment in rainfall runoff is added to by other contaminants from human activities, such as pesticides, nutrients, and toxic substances. Intermittent streams are often supplemented from gray water drainage in residential communities. Leaky septic systems and runoff from animal operations result in high loads of bacterial contamination present in gut streams, one of the main causes of contamination of beaches after rainfall events (DEP 2004).