This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

How to increase initial abstraction in CivilStorm for a given catchment from 0.2S to 0.3S?

Greetings,

I have reasons to adopt a higher initial abstraction in some of my catchments so rather than the 0.2S that would be in default implementation of SCS unit hydrograph method in CivilStorm (it is 0.2S, right?) would like to force a 0.3S? How can i do that?

In addition, can I use Area Reduction Factors in Civil Storm catchment (where/how?) (all modeling is SCS unit hydrograph, SWMM...etc)

thanks

Parents
  • Hello,

    To adjust the initial abstraction, you would need to be using the Unit Hydrograph runoff method and the Horton Loss Method. If you do this, you can adjust the initial abstraction in the catchment properties or the Hydrology alternative. You can find information on this in the "Hydrology Alternative" topic in the Help menu (File > Help > CIvilStorm Help). If you are using the SCS CN runoff method, it doesn't appear that you can adjust this value. 

    For more information on initial abstraction, see this link.

    For the Area Reduction Factor, there appears to be information on this in the Help documentation as well, in the topic "Storm Data Dialog Box". There is a mention on an areal reduction factor for the storm data type "Flood Estimation Handbook (UnitedKingdom)". You can find information on this in the Help documentation. If that isn't the information you are looking for, please provide some further details.

    Regards,

    Scott

    Answer Verified By: A  

  • Thanks Scott. I had a second though about this and felt like defining those specific catchments directly in civilstorm even with higher initial abstraction may not be giving an accurate representation. I originally delineated those specific large upstream catchments using GIS tools (DTM geo-spatial processing methods) but they had a large coverage each (large area) and long Tc (undeveloped areas). Plugging the catchments areas, CN numbers and Tc into the catchment characteristics in CivilStorm would result in a run off hydro-graph per each catchment that I felt is high. A HEC HMS model is expected to give similar results using SCS unit hydro-graph method, so I opted to build a HEC RAS model of these upstream catchments and ran a precipitation on grid simulation and measured flow at the downstream of these specific catchments (via generating a flow hydro-graph at outlet). The result is significantly less indicating that considerable portion of the run-off will not reach the outlets of these catchments where culverts are located (that is where our Civilstorm model starts within the project boundary). Of course this is largerly influence by the DTM nature and land cover. However the grids of the 2D mesh are coarse (100x100m) but any refinement leads to error no. 7 (out of memory) as my device becomes incapable of running the resulting 2D model. I will see if i can get around that by breaking it down to multiple files.

    still thinking which hydro-graph to use as input to our civilstorm model downstream of these areas, the HEC HMS (or equivalently the CivilStorm catchment run off) or that generated from a precip on grid run... guess OpenFlows Flood would have come handy in this investigation as another tool to cross check things!

  • As an update, HEC RAS sounds unstable with the kind of DTM and other things for this specific case .... guess better off without till we get access to better means to investigate 

Reply Children
No Data