This project was to determine the changes in morphology and riparian vegetation that have occurred in the Alberta reaches of Peace River by constructing maps of river morphology and principal riparian vegetation communities from air photographs taken at various dates. The intention is to complete maps at 5 dates, including 1950, so that pre-regulation changes can be measured. Mapping was completed in 4 major reaches, totalling some 612 km of the 1050 km course of the river in Alberta. The maps were constructed in an analytical stereoplotter and the files exported to a GIS for manipulation and map production. In addition field work was undertaken in 1994 to provide ground truth for interpreting the vegetation communities.
At this writing, the maps have been completed for 1968 and 1993, so changes that have occurred over the 25 years of regulation can be summarised (the 1968 coverage is actually constructed from available photography taken in several years near the nominal date). Each complete set of maps comprises 40 sheets at 1:20 000 that approximately correspond with the Alberta digital topographic mapping In addition, extended vegetation mapping was provided on the 1993 maps to show the valleyside vegetation beyond the riparian zone. Morphological changes have been summarised in 31 subreaches of 10 to 25 km length, which reasonably samples the riffle/pool scale along the river. River morphology has been summarised in six major elements, water surface, unvegetated bar surface, vegetated bar surface, island surface, floodplain surface, and tributary alluvial fans within the floodplain. Changes amongst all combinations of these features are available between each date of mapping.
Changes during the 25 years since regulation have included substantial narrowing of the river in major reaches 1 and 3 (the proximal gravel-bed reach and the proximal sand-bed reach), but much less narrowing in the remaining two reaches. Most of Reach 2 was formerly confined and this probably limits the adjustment that will occur. Reach 4, in the Slave Lowland, has different morphology which preconditions less rapid adjustment. Where adjustments have occurred they have dominantly been achieved by riparian vegetation succession onto abandoned bartops and into abandoned side channels. Hence the adjustment process thus far has largely been passive and has depended in a significant way upon riparian succession.
The dominant pattern of riparian succession has been the establishment of scattered shrubs and grasses on the upstream gravel bar surfaces but, once sand becomes trapped on the bartop a continuous shrub cover develops. Downstream, banded galleries of shrubs have established on bar surfaces surrounding old island cores. The changes are most extensive in areas with substantial island development where the river always has been least stable. These are places where bed material is transiently stored on its way down the river. They will remain the sites of main instability and will ensure some renewal o f the early, allogenic plant succession.