River Classification for Management: The Geomorphology of the Sabie River in the Eastern Transvaal

Niekerk, A. W. van; Moon, B.P.

doi:10.1080/03736245.1995.9713594

Cited by 59 publications

(67 citation statements)

References 11 publications

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“…The Mpumalanga region has been subject to uplift in the recent geological past (10 ka to 100 ka BP), resulting in incision into bedrock generating a channel that has a 'floodplain' restricted by the width of incision into bedrock. This incised feature has been termed the macro-channel (van Niekerk et al, 1995), as opposed to the smaller, perennially flowing active channels and seasonally flooded bedrock and alluvial features within its confines.…”

Section: Study Site Catchment and Channel Characteristicsmentioning

confidence: 98%

“…It is underlain by a wide variety of bedrock lithologies, comprising sedimentary, intrusive and extrusive igneous and metamorphic rocks. Lithological differences control the longitudinal slope profile of the Sabie River and consequently the geomorphological form (van Niekerk et al, 1995;Cheshire, 1994). The Mpumalanga region has been subject to uplift in the recent geological past (10 ka to 100 ka BP), resulting in incision into bedrock generating a channel that has a 'floodplain' restricted by the width of incision into bedrock.…”

Section: Study Site Catchment and Channel Characteristicsmentioning

confidence: 99%

“…The geomorphological structure of the river has been examined by van Niekerk et al (1995). They identified five primary channel types, each composed of specific morphological units, with associated flow resistance components (Table I).…”

Section: Study Site Catchment and Channel Characteristicsmentioning

confidence: 99%

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The frictional resistance characteristics of a bedrock‐influenced river channel

Moon

Broadhurst

James

2004

Earth Surf Processes Landf

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Much of the published literature relating to reach-scale total flow resistance concentrates on alluvial rivers and little mention is made of the more extreme resistance found in bedrock-influenced river systems. This paper presents the results of a detailed investigation of total flow resistance variation for five channel types on the Sabie River, South Africa (cohesive mixed anastomosed, uncohesive mixed anastomosed, mixed pool-rapid, alluvial braided and alluvial single thread) over a range of discharges. Manning's 'n' and Darcy-Weisbach f resistance coefficients are calculated using Barnes' methodology (H. H. Barnes, US Geological Survey Water Supply Paper 1849, 1967). These data are analysed at the scales of channel type and morphologic unit and the resultant resistance values are compared with the literature. Generally the low-flow friction values estimated for the bedrock-influenced channel types are higher than any reported. Flow resistance quantification of the alluvial channel type study sites on the Sabie River produced values slightly higher than earlier studies of similar morphologies. In situations where significant areas of irregular bedrock are exposed (cohesive mixed anastomosed and mixed pool-rapid channel types) the high flow resistance coefficients at low discharges probably reflect energy dissipation due to hydraulic jumps and internal distortions; however, these values fall as discharge increases to values comparable to those recorded for step-pool rivers. It is suggested that the slightly elevated resistance coefficients recorded in the alluvial channel types are the result of the vegetation roughness component, operating when the macro-channel bar features are inundated. Copyright

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Section: Study Site Catchment and Channel Characteristicsmentioning

confidence: 98%

Section: Study Site Catchment and Channel Characteristicsmentioning

confidence: 99%

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The frictional resistance characteristics of a bedrock‐influenced river channel

Moon

Broadhurst

James

2004

Earth Surf Processes Landf

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“…Each site was located within a confined river setting with confinement provided by either bedrock or highly resistant macrochannel banks. Macrochannels, or compound channel-in-channels, have been described in a range of hydrologically variable settings globally (Woodyer, 1968;Graf, 1988;Gupta et al, 1995Gupta et al, , 1999Van Niekerk et al, 1995) and are a common channel form in SEQ (Croke et al, 2013). Macrochannels are characterized by a small inner channel and associated benches set within a much larger channel that operates as a conduit for high magnitude floods (Croke et al, 2016a).…”

Section: Figurementioning

confidence: 99%

Beyond the gorge: Palaeoflood reconstruction from slackwater deposits in a range of physiographic settings in subtropical Australia

et al. 2017

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The application of palaeoflood hydrology in Australia has been limited since its initial introduction more than 30 years ago. This study adopts a regional, field-based approach to sampling slackwater deposits in a subtropical setting in southeast Queensland beyond the traditional arid setting. We explore the potential and challenges of using sites outside the traditional physiographical setting of bedrock gorges. Over 30 flood units were identified across different physiographical settings using a range of criteria. Evidence of charcoal-rich layers and palaeosol development assisted in the identification and separation of distinct flood units. The OSL-dated flood units are relatively young with two-thirds of the samples being <1000 years old. The elevation of all flood units have resulted in estimated minimum discharges greater than the 1% annual exceedance probability. Although these are in the same order of gauged flood magnitudes, >80% of them classified as 'extreme event'. This study opens up the renewed possibility of applying palaeoflood hydrology to more populated parts of Australia where the need for improved estimation of flood frequency and magnitude is now urgent in light of several extreme flood events. Preliminary contributions to improve the understanding between high magnitude floods and regional climatic drivers are also discussed. Recognised regional extreme floods generally coincide with La Niña and negative IPO phases, while tropical cyclones appear to be a key weather system in generating such large floods.

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“…Macrochannels, or compound channel-in-channels, have been described in a range of hydrologically-variable settings globally (Woodyer 1968;Graf 1988;Gupta 1995;Gupta et al 1999;Van Niekerk et al 1995) and are a common channel form in SEQ (Croke et al 2013). …”

Section: Site Selection and Physiographical Settingsmentioning

confidence: 99%

Extreme flood events in South East Queensland: evidence and implications

Lam¹

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The use of flood frequency analysis (FFA) to estimate both the magnitude and frequency of the design flood is severely limited by short gauging records. This thesis seeks to improve our understanding of the frequency and magnitude of extreme flood events, with an aim to advance flood risk management and policy planning through the integration of spatial and temporal extreme flood information. This research undertakes a field-work based regional study, collecting slackwater deposits (SWDs) as extreme flood archives and incorporates these as palaeoflood record of extreme flood events for SouthEast Queensland (SEQ).To do so, this study must first define an extreme flood, which is undertaken through the derivation of an Australian Envelope Curve (AEC). The resultant approach represents a significantly improved method to produce an AEC which comprises data from ~2700 gauges in SEQ.An alternative approach to flood frequency is also investigated in the form of a Probabilistic Regional Envelope Curve (PREC) approach which integrates additional spatial information, from homogenous regions. Results indicate that for gauges with either too few, or too many, extreme flood events, the PREC method shows significant changes to the estimated discharges of low % Annual Exceedance Probability (AEP) flood quantiles. A decision making process is provided to ascertain when this method is preferable for FFA.This thesis also examines historical and palaeoflood records that can provide significant upper-tail flood information, often missing from short gauging records. Palaeoflood studies and records have been spatially limited to bedrock settings, in climatic regions outside the subtropical environs of SouthEast Queensland. Reliable historical records are also temporally limited to the last ~200 years of European settlement. This study produced results on the timing and magnitude of past floods from over 30 SWDs across five catchments in the region, spanning a variety of depositional settings, contributing catchment areas, and discharge magnitude. Sensitivity analyses included tests for stable boundary conditions essential for reliable discharge reconstruction. Results show that cross sectional changes due to either aggradation or incision result in resultant changes in discharge that are within the uncertainty range for most of the concerned % AEP flood quantiles.Additional temporal extreme flood information derived from both historical and palaeoflood records are also integrated with gauge records for FFA. This approach reveals that a significant reduction in uncertainty associated with the estimated discharge of a flood quantile can be achieved.Importantly, the uncertainty associated with the 1% AEP flood discharge is reduced by 50-74%. iii

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River Classification for Management: The Geomorphology of the Sabie River in the Eastern Transvaal

Cited by 59 publications

References 11 publications

The frictional resistance characteristics of a bedrock‐influenced river channel

The frictional resistance characteristics of a bedrock‐influenced river channel

Beyond the gorge: Palaeoflood reconstruction from slackwater deposits in a range of physiographic settings in subtropical Australia

Extreme flood events in South East Queensland: evidence and implications

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