Processes and Forms of Alluvial Fans

Blair, Terence C.; McPherson, John G.

doi:10.1007/978-1-4020-5719-9_14

Cited by 162 publications

(248 citation statements)

References 177 publications

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“…Mass-wasting events deliver the sediments to drainages in the mountainous catchment. The material is transported via high-gradient channels during rainfall events, with the sudden deceleration of flow at the gently sloping mouths causing the distinctive radial deposition of sediment across the unconfined valley floor (Blair & McPherson, 2009;Hargitai, 2015). While Forest Creek and Scour Stream result in spatially isolated alluvial fans corresponding to the size of each channel, the proximity of Bush Stream and Black Birch Creek has resulted in the fans coalescing laterally (Figure 7).…”

Section: Post-glacial Landformsmentioning

confidence: 99%

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Glacial geomorphology of the Brabazon & Butler Downs, Rangitata Valley, South Island, New Zealand

2017

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The inland valleys of New Zealand's South Island were heavily glaciated during the last glacial cycle. Subsequent fluvial incision has eroded out glacial deposits from the valleys in many locations, making it difficult to reconstruct glacial dynamics and chronology. The Brabazon and Butler Downs lie in a fault-controlled intra-montaine basin that has been largely protected from fluvial erosion and the area contains extensive evidence for multiple glacial margins. This paper presents a detailed glacial geomorphology map of the Brabazon and Butler Downs at a scale of 1:20,000. Glacial landforms have been mapped and subdivided into three main zones: an upper zone distinguished by a flight of kame terraces, a middle zone containing kettles and meltwater channels, and a lower zone of lateral moraines. The new map provides insight into former glacial environments in the region and provides a related framework for future paleoclimate reconstructions. ARTICLE HISTORY

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Section: Post-glacial Landformsmentioning

confidence: 99%

“…These layers alternate with finer, better sorted sediments laid down during less energetic events (Blair & McPherson, 2009). …”

Section: Post-glacial Landformsmentioning

confidence: 99%

Glacial geomorphology of the Brabazon & Butler Downs, Rangitata Valley, South Island, New Zealand

2017

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“…Moreover, alluvial fans are made of larger size sediments which may have some degree of cohesive material that lies on a steep slope. These two characteristics could lead to "avulsion", formation of new channels during flooding events, which causes major flow path displacement (Blair and McPherson, 2009). Estimation of flood hazards on alluvial fans has been a major dispute among hydrologists for many years (Gaume et al, 2009;Bedrossian et al, 2014;Nguyen et al, 2014;Vennari et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Enhancing flood hazard estimation methods on alluvial fans using an integrated hydraulic, geological and geomorphological approach

Mollaei

Davary

Hasheminia

et al. 2018

Nat. Hazards Earth Syst. Sci.

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Abstract. Due to the uncertainty concerning the location of flow paths on active alluvial fans, alluvial fan floods could be more dangerous than riverine floods. The United States Federal Emergency Management Agency (FEMA) used a simple stochastic model named FAN for this purpose, which has been practiced for many years. In the last decade, this model has been criticized as a consequence of development of more complex computer models. This study was conducted on three alluvial fans located in northeast and southeast Iran using a combination of the FAN model, the hydraulic portion of the FLO-2D model, and geomorphological information. Initial stages included three steps: (a) identifying the alluvial fans' landforms, (b) determining the active and inactive areas of alluvial fans, and (c) delineating 100-year flood within these selected areas. This information was used as an input in the mentioned three approaches of the (i) FLO-2D model, (ii) geomorphological method, and (iii) FAN model. Thereafter, the results of each model were obtained and geographical information system (GIS) layers were created and overlaid. Afterwards, using a scoring system, the results were evaluated and compared. The goal of this research was to introduce a simple but effective solution to estimate the flood hazards. It was concluded that the integrated method proposed in this study is superior at projecting alluvial fan flood hazards with minimum required input data, simplicity, and affordability, which are considered the primary goals of such comprehensive studies. These advantages are more highlighted in underdeveloped and developing countries, which may well lack detailed data and financially cannot support such costly projects. Furthermore, such a highly cost-effective method could be greatly advantageous and pragmatic for developed countries.

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“…This abrupt change causes it to deposit its sedimentary load into an alluvial fan (Bull, 1977;Rachocki and Church, 1990;Blair and McPherson, 1994;Harvey et al, 2005;Blair and McPherson, 2009). As the river builds this sedimentary structure, its bed rises above the surrounding land, and its channel becomes unstable.…”

Section: Introductionmentioning

confidence: 99%

“…In general, the slope steepens when this ratio increases (Parker et al, 1998a, b). At first sight, the shape of P. Delorme et al: Self-similar growth of a bimodal laboratory fan an alluvial fan is well approximated by a cone, but a closer look often reveals a steeper slope near the apex (Le Hooke and Rohrer, 1979;Blair, 1987;Blair and McPherson, 2009;Miller et al, 2014). Possible explanations for this include the decrease in sediment discharge caused by deposition (transport hypothesis) or the downstream fining of the sediment (threshold hypothesis) (Blissenbach, 1952;Rice, 1999;Stock et al, 2008;Miller et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Self-similar growth of a bimodal laboratory fan

et al. 2017

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Abstract.Using laboratory experiments, we investigate the growth of an alluvial fan fed with two distinct granular materials. Throughout the growth of the fan, its surface maintains a radial segregation, with the less mobile sediment concentrated near the apex. Scanning the fan surface with a laser, we find that the transition between the proximal and distal deposits coincides with a distinct slope break. A radial cross section reveals that the stratigraphy records the signal of this segregation. To interpret these observations, we conceptualize the fan as a radially symmetric structure that maintains its geometry as it grows. When combined with slope measurements, this model proves consistent with the sediment mass balance and successfully predicts the slope of the proximal-distal transition as preserved in the fan stratigraphy. While the threshold-channel theory provides an order-of-magnitude estimate of the fan slopes, driven by the relatively high sediment discharge in our experimental system, the actual observed slopes are 3-5 times higher than those predicted by this theory.

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Processes and Forms of Alluvial Fans

Cited by 162 publications

References 177 publications

Glacial geomorphology of the Brabazon & Butler Downs, Rangitata Valley, South Island, New Zealand

Glacial geomorphology of the Brabazon & Butler Downs, Rangitata Valley, South Island, New Zealand

Enhancing flood hazard estimation methods on alluvial fans using an integrated hydraulic, geological and geomorphological approach

Self-similar growth of a bimodal laboratory fan

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