A new modified spatial approach for monitoring non-perennial river water availability using remote sensing in the Tankwa Karoo, Western Cape, South Africa
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Date
2021
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AJOL
Abstract
Non-perennial rivers (N-PRs) make up two thirds of all rivers in South Africa, yet many are ungauged.
Traditionally, it has been assumed that when a flow is recorded, there is water throughout that river. These
assumptions have led to incorrect estimations of available water resources. This work thus aimed at developing
a new spatially explicit framework, for monitoring river water availability in a N-PR system. The Tankwa River
in South Africa was used for testing this approach. The length of the river reach with water was determined
using the Sentinel-1 and Sentinel-2 data derived indices. Image thresholding was applied to Sentinel-1, and
the normalised difference water index (NDWI) to Sentinel-2. Sentinel-2 yielded an overall accuracy (OA) of
85%, whereas Sentinel-1 yielded an OA of 38%. The analysed reach of the Tankwa River had an actual length
of 9 244 m. Based on the performance of Sentinel-2 data, further analysis was undertaken using Sentinel
images acquired during the months of February, May and July of 2016. The results indicated that the lengths
of the reaches of inundated Tankwa River were 2 809 m, 3 202 m and 2 890 m, respectively. Overall, the
findings of this study show that an estimated length of a river inundated by water can be determined using
new-generation Sentinel data and these results provide new insights on the dynamics of N-PRs – a previously
challenging task with broadband multispectral satellite datasets.
Description
Keywords
Water availability, Remote sensing, Non-perennial rivers, Water resource management, South Africa
Citation
Seaton, D ., & Dube, T. (2021). A new modified spatial approach for monitoring non-perennial river water availability using remote sensing in the Tankwa Karoo, Western Cape, South Africa. Water SA, 47(3), 338–346. https://doi.org/10.17159/wsa/2021.v47.i3.11862