In varying ways, hydrologists and soil scientists learn ways to identify alluvial soils as compared to colluvial, flood marks, debris lines floated along margins, etc. If flood was recent and below populated areas, you might find remnants of floating debris in trees, erosion wear line exposed on high banks.

Thank you for your response, sounds promising but sounds like I need a high resolution imagery over my area but again in the presence of high cloud content I wonder if it will render any clear image for a meaningful analysis. But I will certainly will give it a try to find a freely available high resolution imagery with few days return period.

Any more suggestions are still welcome.

Thank you.

I was talking more about collecting any known or recognizable field points (flood heights, marks), and compare with the 1 SAR developed. I forgot to mention, besides soils and hydrology, some vegetative species accept varying degrees of flooding, others not. If you have flood discharge estimates of various floods, HEC RAS and Rivermorph software are a few examples if you have channel and floodplain cross sections. LiDAR coverage may give more elevation and channel location detail. With clear water, green LIDAR can provide some help in channel morphology and type of stream, gradients, aggrading or degrading channel conditions. Gullies typically have no floodplain, just a terrace. Braided streams have excessive sediment loads and unstable channels, excessive and frequent flooding, except for anastomosed braided systems, heavily controlled by dense stable vegetation or forests. If you gave full view of ground or road surface, high resolution photos may help, and infrared often show up wet areas or vegetation changes such as bottomland hardwoods in riparian area as different from pine in uplands for some landscapes. Discussing with soil scientist used to mapping soils, hydrologist and ecologist familiar with the area will help refine estimates if remote sensing is only approach to be used. If travelling to flooded communities, some will augement various flood heights on bridges, buildings, etc. for retention of public record. As with some locations, the severest floods of record are cyclonic events as monsoon and this can be greatly increased when have warm severe rain on snow event.

Validation

1. Selected field visit collect georeferenced points and check.

2. Get hold of past flooded areas and superimpose if falls within it can assumed to be ok.

3.Go for modelling taking discharge validate with SAR map

William F. Hansen Hi,

Thank you for your elaborated answer and suggestions.But, I do not have any cross section data or any Lidar coverage and the suggestions you provided are insightful but my SAR flood extent is of a historical flood event, hence field survey is not relevant in this case.

C M Bhatt ,Hi my SAR flood map is of a historical flood event and there seems to be an areal photograph of one of the smaller region within my Study area. Similarly, I found a SAR flood extent map for another smaller region within my study area. Perhaps I could use them for validating my result ? but how can I quantify the level of accuracy statistically, apart from just visually looking checking them?

Since you are mapping historical flood event. If any published study is there get statistics and try to match with your derived figures. Statistical validation may have variations with surveys done through ground and images. However best way to assure is visit flood mapped areas randomly and have validation from locals about previous event.

You can look for commercially available satellite imageries. Every county maintains a flood inventory maps on a small scale. This can also serve the purpose.

In worst case scenario, though expensive, drone images can also be used for validating the flood extent.