=== versions ===
python 3.12.0 | pysheds 0.5 | numpy 2.5.4 | rasterio 1.5.2 | geopandas 1.2.0 | shapely 2.2.0

=== NRFA station 28001: Derwent at Yorkshire Bridge ===
gauge at British National Grid 419810 E, 385090 N | catchment area 126.0 km² (IHDTM 126.71 km²) | altitude 160.0–631.2 m | drainage density 1.138 km/km²
NRFA boundary polygon: 126.70 km²

=== DEM ===
833 x 700 cells of 30 m (EPSG:27700) | elevation 129.7–634.5 m | missing cells 0

=== condition the DEM ===
single-cell pits raised: 1,440
cells raised by depression filling (beyond the pits): 6,936 (1.2%) | max fill 60.2 m | volume 22.10 million m³
deepest fill at (415635, 381525), DEM 224.0 m raised to 284.2 m
flat cells after filling: 14,869; resolve_flats adds a tiny gradient so they drain

=== D8 flow direction and accumulation ===
largest upstream area in the grid: 196.3 km²
flow directions: E 11.9%, SE 12.3%, S 15.0%, SW 12.0%, W 11.1%, NW 9.6%, N 14.6%, NE 13.5%

=== pour point ===
gauge cell drains 126.37 km² before snapping
snapped to (419790, 385080), 22 m from the gauge; that cell drains 126.4 km²

=== catchment ===
delineated area 126.38 km² vs NRFA 126.0 km² (+0.3%); vs NRFA boundary polygon 126.70 km²
IoU with the NRFA boundary 0.988 | only in ours 0.61 km² | only in NRFA 0.94 km²
              min    10%  median    90%    max
GLO-30 (m)  162.9  285.0   422.8  525.8  629.1
NRFA (m)    160.0  279.3   424.7  528.7  631.2
mean elevation 417 m (NRFA ALTBAR 416 m)
longest flow path 19.9 km; mean flow path 11.34 km (NRFA DPLBAR 11.21 km)

=== stream network ===
channel heads at 0.5 km²: 127 segments, 109.5 km, highest Strahler order 4
          segments  length_km
strahler                     
1               64       48.1
2               44       37.6
3               17       22.2
4                2        1.5
drainage density 0.867 km/km² (NRFA DRAINDENS 1.138)

threshold sensitivity:
 threshold_km2  drainage_density  max_strahler
          0.10             1.652             5
          0.25             1.155             5
          0.50             0.867             4
          1.00             0.665             4
          2.00             0.497             3
          5.00             0.362             3

=== EA Water Framework Directive catchments ===
            id                                         name  kind  area_km2  share_inside
GB104028057960               Derwent from Source to Westend river     20.56         0.995
GB104028057950          Westend Catchment (trib of Derwent) river     14.92         0.999
GB104028057930                  Ashop from Source to Alport river     27.82         0.990
GB104028057940             Alport Catchment (trib of Ashop) river     11.34         0.992
GB104028057910                 Ashop from Alport to Derwent river     10.19         0.992
GB104028057900 Highshore Clough Catchment (trib of Derwent) river      9.84         0.994
GB104028057880                  Derwent from Westend to Wye river    142.84         0.219
    GB30432299                             Howden Reservoir  lake      0.62         1.000
    GB30432359                      Derwent Upper Reservoir  lake      0.70         1.000
    GB30432459                          Ladybower Reservoir  lake      1.97         1.000
river water bodies more than half inside: 6, 94.67 km² together; IoU with our catchment 0.740

=== export ===
wrote derwent_catchment.gpkg (layers: catchment, streams, nrfa_catchment, ea_wfd_waterbodies, pour_point) and flow_accumulation_km2.tif
figures written