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Late Wisconsinan ground moraine in the Rocky Mountain Trench, southeastern British Columbia, is dissected by meltwater channels which formed during the final retreat of the Cordilleran glacier. Outwash underlying the channels is coarse, poorly sorted, shows large-scale cross-bedding, and was deposited in chan-nel-bar complexes of high-energy proglacial rivers. Length of transport of outwash gravel from till source to channel depositional site is relatively short. The coarse fraction of till is also of local derivation, because lithologies are similar to nearby bedrock lithologies.

Peak discharges calculated from channel morphometry and maximum particle size were 10,000 to 20,000 cubic meters per second, larger than the estimated maximum discharges of several thousand cubic meters per second attributable to summer runoff. Many channels transmitted peak discharges during jökullhlaups from glacial lakes in tributary valleys. An empirical relationship between total volume discharged during documented jökullhlaups and corresponding maximum instantaneous discharges is applied here to Glacial Lake Elk to show that discharges equal to, or larger than, those calculated from channel morphometry were attained during jökullhlaups.

Mean discharge (excluding jökullhlaups) for most of the active channels was estimated to be less than 1000 cubic meters per second; the ratio of maximum instantaneous to mean discharges was about 10:1, but may have exceeded 20:1 in some channels. At low and moderate stages rivers had braided patterns within individual meltwater channels, but during peak flows channel bars were submerged.

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