I am trying to model rainfall-runoff using TOPMODEL in R. The TOPMODEL needs an input called "cumulative delay function". The R documentation says "Flow is routed through a delay function which represents the time spent in the channel system. The parameter delay is used for this. Delay is a matrix with 2 columns. The first column gives the cumulative relative area. The second column gives the average distance towards the outlet (m). One of the papers (Hydrological modelling with TOPMODEL of Chingaza páramo, Colombia) which used TOPMODEL had this table enter image description here

Does anyone know how to derive this table either in R or QGIS/GRASS ?

closed as too broad by PolyGeo Dec 13 '17 at 3:20

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Found help here https://idea.isnew.info/how-to-calculate-the-longest-flow-path-in-grass-gis.html https://idea.isnew.info/r.topmodel.html

  1. Find the longest flow path (LFP) using r.stream.distance
  2. Create outlets at required intervals on the LFP
  3. Find the basins for each of the outlets using r.water.outlet
  4. Find the area of each of the basin as a proportion of the total basin.
  5. A dataframe with two rows - Distance of the outlet from the main outlet, area of the basin corresponding to this outlet as a proportion of the total basin area will form the Cumulative delay function

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