TY - JOUR
T1 - Topographic, Hydraulic, and Vegetative Controls on Bar and Island Development in Mixed Bedrock‐Alluvial, Multichanneled, Dryland Rivers
AU - Milan, D. J.
AU - Tooth, S.
AU - Heritage, G. L.
N1 - Funding Information:
This project was funded through the Natural Environment Research Council (NERC) Urgency grant NE/K001132/1. We would like to thank SANParks for supporting this research. The LiDAR data obtained through this funding are described in Milan, Heritage, and Tooth () and available at http://catalogue.ceda.ac.uk/uuid/a2e82c7f92dc4f389a7fb7e4e6629c9e. The paper was improved through the supportive comments of three anonymous reviewers and the evaluation of the Associate Editor (F. Comiti) and Editor (E.E. Wohl).
Funding Information:
This project was funded through the Natural Environment Research Council (NERC) Urgency grant NE/K001132/1. We would like to thank SANParks for supporting this research. The LiDAR data obtained through this funding are described in Milan, Heritage, and Tooth ( ) and available at http://catalogue.ceda.ac.uk/uuid/a2e82c7f92dc4f389a7fb7e4e6629c9e . The paper was improved through the supportive comments of three anonymous reviewers and the evaluation of the Associate Editor (F. Comiti) and Editor (E.E. Wohl).
Publisher Copyright:
©2020. The Authors.
PY - 2020/5/14
Y1 - 2020/5/14
N2 - We investigate processes of bedrock-core bar and island development in a bedrock-influenced anastomosed reach of the Sabie River, Kruger National Park, eastern South Africa. For sites subject to alluvial stripping during an extreme flood event (~4,470–5,630 m3 s−1) in 2012, preflood and postflood aerial photographs and LiDAR data, 2-D morphodynamic simulations, and field observations reveal that the thickest surviving alluvial deposits tend to be located over bedrock topographic lows. At a simulated peak discharge (~4,500 m3 s−1), most sediment (sand, fine gravel) is mobile but localized deposition on bedrock topographic highs is possible. At lower simulated discharges (<1,000 m3 s−1), topographic highs are not submerged, and deposition occurs in lower elevation areas, particularly in areas disconnected from the main channels during falling stage. Field observations suggest that in addition to discharge, rainwash between floods may redistribute sediments from bedrock topographic highs to lower elevation areas, and also highlight the critical role of vegetation colonization in bar stability, and in trapping of additional sediment and organics. These findings challenge the assumptions of preferential deposition on topographic highs that underpin previous analyses of Kruger National Park river dynamics, and are synthesized in a new conceptual model that demonstrates how initial bedrock topographic lows become topographic highs (bedrock-core bars and islands) in the latter stages of sediment accumulation. The model provides particular insight into the development of mixed bedrock-alluvial anastomosing along the Kruger National Park rivers, but similar processes of bar/island development likely occur along numerous other bedrock-influenced rivers across dryland southern Africa and farther afield.
AB - We investigate processes of bedrock-core bar and island development in a bedrock-influenced anastomosed reach of the Sabie River, Kruger National Park, eastern South Africa. For sites subject to alluvial stripping during an extreme flood event (~4,470–5,630 m3 s−1) in 2012, preflood and postflood aerial photographs and LiDAR data, 2-D morphodynamic simulations, and field observations reveal that the thickest surviving alluvial deposits tend to be located over bedrock topographic lows. At a simulated peak discharge (~4,500 m3 s−1), most sediment (sand, fine gravel) is mobile but localized deposition on bedrock topographic highs is possible. At lower simulated discharges (<1,000 m3 s−1), topographic highs are not submerged, and deposition occurs in lower elevation areas, particularly in areas disconnected from the main channels during falling stage. Field observations suggest that in addition to discharge, rainwash between floods may redistribute sediments from bedrock topographic highs to lower elevation areas, and also highlight the critical role of vegetation colonization in bar stability, and in trapping of additional sediment and organics. These findings challenge the assumptions of preferential deposition on topographic highs that underpin previous analyses of Kruger National Park river dynamics, and are synthesized in a new conceptual model that demonstrates how initial bedrock topographic lows become topographic highs (bedrock-core bars and islands) in the latter stages of sediment accumulation. The model provides particular insight into the development of mixed bedrock-alluvial anastomosing along the Kruger National Park rivers, but similar processes of bar/island development likely occur along numerous other bedrock-influenced rivers across dryland southern Africa and farther afield.
KW - bedrock-core bar, dryland river, mixed bedrock-alluvial, vegetation-morphology interactions, morphodynamic simulation, anastomosed
UR - http://www.scopus.com/inward/record.url?scp=85085516453&partnerID=8YFLogxK
U2 - 10.1029/2019WR026101
DO - 10.1029/2019WR026101
M3 - Article
AN - SCOPUS:85085516453
SN - 0043-1397
VL - 56
JO - Water Resources Research
JF - Water Resources Research
IS - 5
M1 - e2019WR026101
ER -