Messina, A.M.; T.W. Biggs

Contribution of human activities to suspended sediment yield during storm events from a small, steep, tropical watershed

2016

Journal of Hydrology

538

726-742

"Suspended sediment concentrations (SSC) and yields (SSY) were measured during storm and non-storm periods from undisturbed and human-disturbed portions of a small (1.8 km2), mountainous watershed that drains to a sediment-stressed coral reef. Event-wise SSY (SSYEV) was calculated for 142 storms from measurements of water discharge (Q), turbidity (T), and SSC measured downstream of three key sediment sources: undisturbed forest, an aggregate quarry, and a village. SSC and SSYEV were significantly higher downstream of the quarry during both storm- and non-storm periods. The human-disturbed subwatershed (10.1% disturbed) accounted for an average of 87% of SSYEV from the watershed. Observed sediment yield (mass) to the coast, including human disturbed subwatersheds, was 3.9 the natural background. Specific SSY (mass/area) from the disturbed quarry area was 49 higher than from natural forest compared with 8 higher from the village area. Similar to mountainous watersheds in semi-arid and temperate climates, SSYEV from both the undisturbed and disturbed watersheds correlated closely with maximum event discharge (Qmax), event total precipitation and event total Q, but not with the Erosivity Index. Best estimates of annual SSY varied by method, from 45 to 143 tons/km2/yr from the undisturbed subwatershed, 441598 tons/km2/yr from the human-disturbed subwatershed, and 241368 tons/km2/yr from the total watershed. Sediment yield was very sensitive to disturbance; the quarry covers 1.1% of the total watershed area, but contributed 36% of SSYEV. Given the limited access to gravel for infrastructure development, sediment disturbance from local aggregate mining may be a critical sediment source on remote islands in the Pacific and elsewhere. Identification of erosion hotspots like the quarry using rapid, event-wise measures of suspended sediment yield will help efforts to mitigate sediment stress and restore coral reefs."

Suspended sediment yield, Volcanic islands, Land use, Storm events, Coastal sediment yield, American Samoa

doi.org/10.1016/j.jhydrol.2016.03.053

FY13; CRCP Project ID: 198; Project Title: Domestic Coral Reef Conservation Grant Programs; Principal Investigator: Kristine Bucchianeri; CRCP Grant Number: NA13NOS4820013