Dear colleagues,
I took an initiative to map and develop polygons visualizing river channel and how its width extended during a flooding event. Now i would like to measure how the river actually extended (interms of distance).
My suggestion was to draw lines perpendicular to the river channel and use them for my measurements. Unfortunately, i could not find literature to support this or to suggest an alternative approach. If you have any suggestions regarding how others have done the exercise or how you think the exercise can be done more reasonably, please advise me accordingly.
Yours
Patrick
Dear Patrick
In terms of flood plains and how water flows in them the lines you draw should be perpendicular to the flow in the floodplain NOT perpendicular to the channel, which is the way you have sketched them . This is illustrated by the attached image that I have taken from this blog on the river modelling software HEC RASsee http://hecrasmodel.blogspot.com/2012/07/how-to-draw-cross-sections.html
Another useful publication is this: https://www.researchgate.net/publication/258507253_Cross-section_location_in_1-D_models
I hope that this is of help.
Darren
You should note that the light blue lines in the image I have attached are contour lines i.e. points of equal height. I have attached a revised annotated diagram.
Hi Patrick
Use HEC HMS for event modeling at catchment level and HEC RAS for flood mapping in the river channel. Google search along those lines and you will find a lot of literature. Let me know if you need help on the models, or you may also wish to attend regular modelling trainings in Dar es Salaam (reasonably close to your city) organized by www.witekconsulting.com
Best regards
Fredrick
Hi Patrick,
As Darren and Fredrick mentioned, you might need to run a model, either HEC-RAS, HE-HMS and also there's a free version of FloodModeller. These would help you to draw the flood extent on both sides of the river banks (or floodplain). However, if your question is, that you already know the flood extent, which you called it 'New bank boundary' but you wanted to measure the distance perpendicular to the river flow centre-line, you can use QGIS. You need DTM data of the catchment you are interested in. Once you've QGIS, upload the DTM data, install a couple of plug-ins (all free), you draw a line crossing the river section from right bank to left bank, then QGIS will give a cross-section with dimensions. Hope that helps.
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