Few studies have considered downstream changes in bank erosion rates and va
riability along single river systems. This paper reports some preliminary r
esults of an intensive and direct field monitoring exercise of bank erosion
rates on 11 sites along 130 km of the 3315 km(2) Swale-Ouse river system i
n northern England over a 14.5 month period. Data were collected at active
sites using grid networks of erosion pins read at c. 18-30 day intervals an
d bank-line resurveys. Erosion rates were relatively high for a river of th
is scale: spatially averaged bank erosion magnitudes over the 14.5 months v
aried from 82.7 mm to 440.1 mm, although at one highly mobile reach retreat
of 1760 mm was recorded over 4 months. Bank erosion rates tended to peak i
n mid-basin, possibly because of an optimum combination there of high strea
m powers and erodible bank materials, as predicted theoretically by Lawler
(1992, 1995). The piedmont (upland-lowland transition) zone was especially
active. Graphical erosion representations for specific periods, however, sh
owed that bank retreat was often highly localized within individual sites.
Strong seasonal variations in erosion rate were also observed with a signif
icant winter (December-March) peak. A novel finding, however, was the appar
ent downstream increase in the length of the erosion 'season', with measura
ble retreat occurring at the lower sites from September to July. This is in
terpreted as a reflection of a richer mix of bank erosion processes at the
downstream sites, where mass failure, fluid entrainment and weathering proc
esses are all active, with each process group having its own, but overlappi
ng, temporal (seasonal) domain. Copyright (C) 1999 John Wiley & Sons, Ltd.