| || || Ram, Arishma Reshmi|
| || || Rainfall, runoff events and fluvial sediment delivery patterns in a small forested coastal watershed in Southern Viti Levu, Fiji Islands|
Author:Ram, Arishma Reshmi
Institution: University of the South Pacific.
Subject: Rain and rainfall -- Fiji -- Votua Creek Watershed, Runoff -- Fiji -- Votua Creek Watershed, Suspended sediments -- Fiji -- Votua Creek Watershed, Votua Creek Watershed (Fiji)
Call No.: Pac QC 925 .8 .F5 R36 2013
Copyright:Under 10% of this thesis may be copied without the authors written permission
Abstract: Studies on soil erosion and suspended sediment transport in river catchments are scarce in the developing Pacific island nations. Lack of sufficient data for fluvial suspended sediment transport hinders the evaluation of watershed restoration efforts. In Fiji, marine productivity is threatened by land-based activities that increase soil erosion and fluvial sediment delivery to coasts. The present study investigates fluvial sediment dynamics in a naturally forested, steep coastal catchment on the Coral Coast –the Votua watershed– to provide a baseline against which comparisons can be made to similar areas where land-use activities are more intense. The USLE model, combined with GIS, was used to visualize and quantify potential areas of long-term soil erosion risk in the Votua watershed. The catchment was also fitted with an instrument to monitor turbidity in the Votua Creek over an 8 month period from October 2009 to June 2010 in response to rainfall events. Grab samples were also taken during rainfall-runoff events to analyze for TSS to test for the relationship with corresponding turbidity readings. The USLE model produced potential soil loss values ranging from 0 to 907.3 t/ha/yr and an average of 6.4 t/ha/yr for the Votua watershed. The values corresponded well to other studies in Fiji indicating that the USLE can be used as an initial step for estimating potential soil loss for catchments in Fiji where resources and data are scarce. Several rainfall and turbidity variables were calculated for all the analyzed hydrological response events and correlation matrices were developed using these data. Rainfall variables measured for the lower Votua catchment had a significant strong positive correlation with turbidity response parameters. A significant strong positive correlation was found between the turbidity and TSS of the Votua stream. The TSS released by the watershed in a typical El Niño year was calculated to be 0.9 t/ha/yr using data from this project, which corresponded well with the USLE model results reinforcing the view that the USLE model is a reliable tool for watershed management and restoration efforts in Fiji. Events showing clear hysteresis patterns displayed anticlockwise patterns denoting sediments in the Votua catchment are likely to be generated from hill slope erosion, landslide and bank collapse during the high intensity rainfall.