Estimating Flood Magnitude in Ungauged Mountain Channels, Nepal

Wohl, Ellen; Collins, Fort

doi:10.2307/3673701

Cited by 18 publications

(7 citation statements)

References 21 publications

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“…While paleohydrology is generally applied to Holocene floods (100-10 000 years), Jarrett (1990) estimated the peak discharge from the 1976 Big Thompson flood near Loveland, Colorado using a combination of paleohydrology and regional flood frequency estimates. Wohl (1995) applied these techniques in ungaged streams in Nepal where hydrologic data are sparse, or untraceable. We can use this technique to estimate peak flows and their paths following dam removal.…”

Section: Paleohydrologymentioning

confidence: 99%

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Using historic aerial photography and paleohydrologic techniques to assess long-term ecological response to two Montana dam removals

Schmitz

Blank

Ammondt

et al. 2009

Journal of Environmental Management

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Section: Paleohydrologymentioning

confidence: 99%

“…Jarrett (1990) used these methods to determine the recurrence interval of a flood that occurred 20 years prior to analysis, and Wohl (1995) applied them to ungaged streams to determine discharges from events that occurred 40 years ago.…”

Section: Hydrologic Characterizationmentioning

confidence: 99%

Using historic aerial photography and paleohydrologic techniques to assess long-term ecological response to two Montana dam removals

Schmitz

Blank

Ammondt

et al. 2009

Journal of Environmental Management

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“…Manning's n is a major source of uncertainty in numerical hydraulic models(Brunner, 2020a;Klimeš et al, 2014) and we conducted a sensitivity analysis to estimate this uncertainty.Reported flood stages for the 2012 flood are limited to the Seti dam(SANDRP, 2014). Hence, we mapped flood deposits as indicators for peak flow stage, following the methods thatWohl (1995) used to reconstruct glacial lake outburst floods (GLOFs) in eastern Nepal. We mapped flood deposits and inundation limits of the 2012 outburst from an orthorectified 5-m resolution RapidEye satellite image acquired on 18 October 2012, which was the first cloud-free image…”

mentioning

confidence: 99%

Himalayan hazard cascades – modern and medieval outburst floods in Pokhara, Nepal

Fischer

Lehnigk

Lützow

et al. 2023

Earth Surf Processes Landf

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In May 2012, a sediment‐laden flood along the Seti Khola (= river) caused 72 fatalities and widespread devastation for > 40 km in Pokhara, Nepal's second largest city. The flood was the terminal phase of a hazard cascade that likely began with a major rock‐slope collapse in the Annapurna Massif upstream, followed by intermittent ponding of meltwater and subsequent outburst flooding. Similar hazard cascades have been reported in other mountain belts, but peak discharges for these events have rarely been quantified. We use two hydrodynamic models to simulate the extent and geomorphic impacts of the 2012 flood and attempt to reconstruct the likely water discharge linked to even larger medieval sediment pulses. The latter are reported to have deposited several cubic kilometres of sediment in the Pokhara Valley. The process behind these sediment pulses is debated. We traced evidence of aggradation along the Seti Khola during field surveys and from RapidEye satellite images. We use two steady‐state flood models, HEC‐RAS and ANUGA, and high‐resolution topographic data, to constrain the initial flood discharge with the lowest mismatch between observed and predicted flood extents. We explore the physically plausible range of simplified flood scenarios, from meteorological (1000 m3 s−1) to cataclysmic outburst floods (600,000 m3 s−1). We find that the 2012 flood most likely had a peak discharge of 3700 m3 s−1 in the upper Seti Khola and attenuated to 500 m3 s−1 when arriving in Pokhara city. Simulations of larger outburst floods produce extensive backwater effects in tributary valleys that match with the locations of upstream‐dipping medieval‐age slackwater sediments in several tributaries of the Seti Khola. Our findings are consistent with the notion that the medieval sediment pulses were linked to outburst floods with peak discharges of >50,000 m3 s−1, though discharge may have been an order of magnitude higher.

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“…flow velocity) via a relevant physical relationship, such as flow resistance (Williams, 1984). The second approach relies on the identification of palaeostage indicators (PSI) using geomorphic (Baker, 1973;Shroba et al, 1979;Wohl, 1995), sedimentary (Kochel and Baker, 1988;O'Connor et al, 1994); and/or botanical (Gregory, 1976;Hupp, 1988) evidence. If sufficient PSI are identified, hydraulic modelling can be undertaken to retrodict the peak flow discharge required to match the inferred elevation of the former flood.…”

Section: Introductionmentioning

confidence: 99%

The use of one- and two-dimensional hydraulic modelling to reconstruct a glacial outburst flood in a steep Alpine valley

Bohorquez

Darby

2008

Journal of Hydrology

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Summary The hydrologic characteristics of the 1943 outburst flood from the Glacier du Mont Miné, Switzerland, are herein reconstructed using field evidence (palaeostage indicators) in conjunction with shallow water modelling techniques. These techniques rely on accurately characterising the hydraulic roughness of the channel, the water height established as boundary conditions, and the main flow path during the former flood, but the selection of appropriate parameter values can be problematic and hence there is uncertainty in the estimated discharge. In this study, minimal flow discharge estimates derived from one-dimensional modelling were found to vary between 429 and 557 m 3 s À1 as the hydraulic roughness ðk s Þ and water height at the inlet were varied over a realistic range of values (0.8-1.4 m and 3.31-6 m, respectively), whereas flow rates derived via twodimensional modelling were confined in a narrower, lower, range of 358-454 m 3 s À1 . This degree of sensitivity to bed roughness k s , boundary conditions and the spatial dimensions of the modelling approach is, for the one-dimensional modelling, higher than reported in previous studies, but the precision of flow discharge values reconstructed using the twodimensional modelling approach appears to be acceptable, even for floods in the very steep valley (0.1 m/m) that is subject of this study. ª

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Estimating Flood Magnitude in Ungauged Mountain Channels, Nepal

Cited by 18 publications

References 21 publications

Using historic aerial photography and paleohydrologic techniques to assess long-term ecological response to two Montana dam removals

Using historic aerial photography and paleohydrologic techniques to assess long-term ecological response to two Montana dam removals

Himalayan hazard cascades – modern and medieval outburst floods in Pokhara, Nepal

The use of one- and two-dimensional hydraulic modelling to reconstruct a glacial outburst flood in a steep Alpine valley

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