Stream Development in Glacier Bay National Park, Alaska, U.S.A.

Abstract

The effects of hydraulics, sediment supply, channel condition, and riparian vegetation on stream development were examined in a chronosequence of five streams in Glacier Bay National Park where rapid retreat of glacial ice has exposed landscapes of different ages within a confined region. The youngest stream, Wolf Point Creek (deglaciated around 1955), is fed by a remnant glacier and had the highest suspended sediment concentrations of all streams (103-111 mg L-1 at baseflows). The main channel of Wolf Point Creek was relatively wide and stable because of the peak flow buffering effects of the remnant glacier and associated lake. However, the floodplain was periodically inundated and only sparsely vegetated and highly braided. The study reach at Nunatak Creek (deglaciated around 1950) was actively downcutting through fine glacial outwash deposits creating a deeper thalweg and redepositing some material near channel margins. About 100 yr after deglaciation (Ice Valley stream), woody riparian vegetation begins to stabilize streambanks and becomes established on gravel bars where it provides potential sites for incipient woody debris dams. The Ice Valley channel shows only minimal degradation. The increased accumulation of woody material and the subsequent colonization of gravel bars by alder and willow have begun to increase channel and bank stability and pool formation in Berg Bay South (deglaciated around 1830). Berg Bay South appears to be near equilibrium with respect to sediment supply and transport. Berg Bay North, a stream of similar age to Berg Bay South, stabilized more rapidly because of the buffered peak flows and greater sediment trapping efficiency attributed to the lakes and bogs in the north stream system. Fish habitat improves as postglacial streams develop: pools begin to form, riparian cover increases, and sediment transport decreases.