Abstract
Sediment yield dynamics on the Edwards Plateau region of Texas was dramatically influenced by a multi-year drought that occurred there during the 1950s. To assess the effect of this drought on sediment yield, we used the Soil and Water Assessment Tool (SWAT) to identify the factors that contributed erosion and to propose potential mitigation measures in case of future drought recurrence. The basins of interest to this study were Brady Creek One (BC 1) and Deep Creek Three (DC 3), located in McCulloch County, Texas. Although the streams in these basins are not gauged, the land cover and reservoir sediment budgets have been assessed in a past study. Calibration of SWAT flow simulation was accomplished using parameter transfer from a gauging station located in San Saba River. The results showed that sediment yield from storms above 60 mm was five times more during and immediately after drought period than during continuous wet seasons. Approximately half of the total drought period sediment yield was from five major rainstorms. The multi-year drought coupled with historical high grazing intensity resulted in significant loss of plant cover, which was considered critical in determining erosion and sedimentation rates. To test this hypothesis, the model was run for the periods of high land cover (1990s) using the 1950s multi-year drought data which showed that sediment yield was 24% of that simulated for 1950s land cover. It was concluded that maintenance of surface cover could play a critical role associated with multi-year drought extreme events.
Highlights
Droughts are natural disasters that have attracted the attention of environmentalists, ecologists, hydrologists, meteorologists, geologists and agricultural scientists due to the impacts these events may have on natural resources [1]
The land cover scenario coupled with the prevailing mean decadal grazing intensity (Figure 3) were compared to the base case while using the same time series data i.e. rainfall and temperature as model inputs. These analyses showed the impacts of varying cover due to drought coupled with grazing intensity
Parameter transfer using derived metric, which was based on a combination of spatial proximity and physical similarity, was successfully used to extend parameters derived from the San Saba calibration to the BC 1 and DC 3 basins
Summary
Droughts are natural disasters that have attracted the attention of environmentalists, ecologists, hydrologists, meteorologists, geologists and agricultural scientists due to the impacts these events may have on natural resources [1]. The region experienced a series of droughts, with nine episodes between 1889 and 1957 [6]. The most severe was the “drought of record” of 1950s [3], which persisted for six consecutive years in which the most extreme period between 1954 and 1956 had a cumulative rainfall deficit of more than 500 mm [6] [7]. These droughts reduced the vegetative cover density. The occurrences of droughts impact environmental and socio-economic resources and should stimulate mitigation planning for future recurrence [8]
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