In the UK's upland catchments river terraces and alluvial features indicate
a history of periodic aggradation and degradation linked to Holocene chang
es in land use (primarily deforestation) and climate change (altering flood
frequency and magnitude). Although both factors are important, calculating
their individual effects is complicated by the likelihood of their concurr
ent alteration.
To investigate the relative impacts of land use and climate change, a cellu
lar model is applied to the upland catchment of Cam Gill Beck, above Starbo
tton, North Yorkshire. This is divided into 1 million 2 m by 2 m grid cells
, to which a range of process laws are applied. These include approximate e
xpressions for mass movement rates, soil creep, the influence of vegetation
and hillslope hydrology, as well as fluvial erosion and deposition in ten
grain-size fractions. This provides a good representation of valley floor g
eometry while retaining a fully dynamic interaction with the surrounding va
lley sides. Previous applications of this model have shown the detailed for
mation of bars and berms as well as examples of braiding, avulsion and chan
nel change.
Running on a Silicon Graphics Origin 2000 computer, an ensemble of simulati
ons were completed, bracketing a wide range of environmental scenarios invo
lving changes in flood frequency, magnitude and vegetation cover. Over time
-scales ranging from 10 to 100 years, these showed that decreasing tree cov
er and increasing rainfall magnitude individually produced similar 25% to 1
00% increases in sediment discharge, whereas in combination they generated
a 1300% rise. Furthermore, channels formed by the model in response to incr
ease rainfall magnitudes are located where relic channels are found in Cam
Gill Beck, implying that these are the products of previous periods of high
rainfall magnitudes. Copyright (C) 2000 John Wiley & Sons, Ltd.