Can watershed models aid in determining historic lake sediment concentrations in data-scarce areas?

Abstract

In most developing countries, there is a lack of historical sediment data. In Ethiopia, over the past 40 years, sediment concentrations in rivers are periodically measured for determining sediment rating curves. But, no such historical data are available for lakes such as Lake Tana in Upper Blue Nile River basin, greatly hampering the ability to track the trend of environmental pollution. The objective of this study is to determine whether models can be used to estimate the historical record of lake sediment concentrations. In this study, a relationship between reflectance and TSS was developed and 10-year TSS time series data were generated from MODIS /Terra images. The 10-year TSS time series data were used to calibrate and validate an erosion model. The soil and water assessment tool variable source area (SWAT-VSA) model was selected because it has performed well in the Lake Tana basin. The result showed that at monthly timescale, TSS at the river mouth can be replicated with Nash–Sutcliffe efficiency (NS) of 0.34 for calibration and 0.21 for validation periods. Percent bias (PBIAS) and ratio of root mean square error (RSR) to the standard deviation of measured data are all within range. Given the inaccessibility and costliness to measure TSS at river mouths to a lake, the results found here are considered best estimates for suspended sediment budget in water bodies of the basin. However, direct measurement or improved models should yield better results.