Drainage Density Ruggedness (DDR)

The dimensionless product of drainage density (stream length per unit area – km/km2) and total elevation relief.

— Melton, 1957

The difference between the highest and lowest points in the watershed, relative to watershed length (in km).

— Schumm, 1956

The potential for rapid runoff delivery to and through streams, which may contribute to harmful flood events

— Patton and Baker, 1976

Method

1. Generate relief for BC FWA Assessment Watersheds by overlaying with the BC 1:20k DEM

2. Calculate drainage density per watershed polygon (km of streams / km2 of watershed) using this definition of 'stream':

   • FWA river polygon centerlines
   • FWA primary/secondary flow lines (ie, edge_type IN (1000,1100,2000,2300) and not within a lake/reservoir/wetland waterbody)

3. Calculate DDR as drainage density * relief

4. Classify DDR:

   • class 1: less than 2000 km/km2
   • class 2: 2000-4000 km/km2
   • class 3: greater than 4000 km/km2

Requirements

• BC FWA loaded to postgres database defined by $DATABASE_URL via fwapg
• jq, parallel
• BC DEM

Processing

./ddr.sh

Output

ddr.csv

column	description
watershed_feature_id	Assessment watershed unique id
elevation_min	Minimum elevation in the watershed (m)
elevation_max	Maximum elevation in the watershed (m)
elevation_relief	The elevation relief in the watershed (m)
stream_length_km	Length of stream in the watershed (km)
watershed_area_km2	Area of the watershed (km2)
drainage_density	Total length of streams / total area of watershed (km/km2)
drainage_density_ruggedness	Stream density as a function of relief (km of streams / km2 of watershed) * relief
drainage_dens_rugged_cls_num	Numeric classification of DDR: (1: <2000; 2: 2000-4000; 3: >= 4000)