Hi,
I am looking for simple equation to calculate a river inundated floodplain area as a function of its stream flow rate (and perhaps average depth). Can anyone suggest such formula ( ideally with a reference)?
Many thanks
I hope you should have to follow "Manning's equation" with emphasis on the width of the rivers/streams.
Thanks for your response. I am not sure how "Manning equation" can be used to calculate inundated floodplain area. Manning equation can be used to calculate stream area (cross section) but it will not give inundaated floodplain area i.e. the area on a river bank which will be covered when flow rate increases (flood happens). Besides using Manning equation needs values of stream's slope and roughness coefiicient ti be know. These are not available to me for the case I am working on. So, I was wondering if there exist a simplified equation that uses flow rate and average depth to calculate inundated floodplain area.
Due to differences in stream type, topography, climate, etc., I doubt if you will find a simple equation to apply. Without extensive stream flow records and channel morphology measures, you may be best off in estimating this extent with soil maps produced by soil scientists, who are experienced in looking at flood Indicators in alluvial materials. Flood stage indicators and local observations are also helpful to consider. Entrenched streams as gullies have a flat terrace that appears to be a floodplain, but no longer functions as one. Braided streams have lost channel capacity to extent that they flood frequently, perhaps to full extent of valley width. High resolution aerial photos and LIDAR may be helpful in producing high resolution DEM useful with some field verification and spatial analysis in estimating channel types, gradients, entrenchment and flood zones. It is difficult to assume flooding extent without field measures and verification. If equations are obtained, try them out on local gauged streams relative to discharge rates, channel depth at flooding (bankfull), flood frequency, widths of flooding relative to valley type, gradients, channel type and morphology, roughness, etc. If the equation can be locally validated for certain channel types and flooding conditions, it may have applications to similar conditions. I know of no simple equation or analysis that would meet your intent. Dave Rosgen has suggested if bankfull indicators are validated in the field, 2 times bankfull depth at thalweg should yield floodprone area (~50 year event). His early work was reviewed by Luna Leopold, so this may be a useful rule of thumb.
Many thanks William for your detailed answer. I'll look into those two papers. I think the methodolgy of Dave Rosgen and/or Luna Leopold can be applicable to my case.
Hello. Hi,
I understand that what you want is a simple index, which relates the hydrological state of the river to the wet surface, covered by water. Then, analyze the elasticity of wetlands in each stretch of the river.
I developed the Index of elasticity, which applies a very simple formula: the surface covered by water in the hydrological state of extreme high waters / the surface covered by water in a situation of maximum drought. For this, we use Landsat or Google Earth images, or others.
Knowing the registers of the river's hydrometric levels, in a historical series, you can relate the flooded surface in each hydrological phase.
Here, below, I place some references. You can also use our free PULSO application to analyze the variability of structures and fluvial processes subjected to recurrent phenomena (pulses). Processes whose variability responds to a sinusoidal function:
www.neiff.com.ar
References in RG:
Dear Majed,
You. I could use the Elasticity Quotient:
S2/S1
Where: S2 = floodplain surface area covered by water in maximum historical flooding;
S1= surface area occupied by water during the historical extreme drought.
For this, you. will use satellite images (landsat, Google Earth, others).
You can search in my Research Gate:
Neiff, JJ.Iriondo, M. and R. Carignan. 1994
Neiff, 1996;2001.
Also, could be used with the free application PULSE: www.neiff.com.ar
Best wishes.
JJ
Dear JJ,
Thanks for your help. I think that's what I was looing for.
Regards,
Majed
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