Debris-covered Area Research Articles

Application of a conceptual precipitation-runoff model (HYGYMODEL) in a debris-covered glacierized basin in the Langtang Valley, Nepal Himalaya

A conceptual precipitation–runoff model (HYCYMODEL) is used to simulate the daily runoff from the 67% glacierized Lirung basin (16% of which is covered by debris). The average thermal resistance of the debris cover of the Lrung Glacier has been estimated from the surface temperature of the debris, which was obtained from Landsat 5 (TM Band 6) images. This enabled calculation of the melt rate of the debris-covered area of the glacier using meteorological data collected at a nearby weather station. The calculated discharge results are roughly compatible with the observed daily discharges.

Effects of Woody Debris on Anadromous Salmonid Habitat, Prince of Wales Island, Southeast Alaska

The effects of woody debris on anadromous salmonid habitat in eight streams on Prince of Wales Island, southeast Alaska, were investigated by comparing low-gradient (1-9%) first- or second-order streams flowing through either spruce-hemlock forests or 6-10-year-old clear-cuts, and by observing changes after debris was selectively removed from clear-cut reaches. Woody debris decreased the rate of shallowing as discharge decreased, thus helping to preserve living space for fish during critical low-flow periods. Debris dams were more frequent in clear-cut streams (14.9/100 m), which contained more debris, than in forested streams (4.2/100 m). As a result, total residual pool length (length when pools are filled with water but there is no flow) and length of channel with residual depth greater than 14 cm—the depth range occupied by 84% of coho salmon (Oncorhynchus kisutch)—were greater in clear-cut streams than in forested streams. Greater volumes of woody debris in clear-cut streams produced greater storage of fine sediment (<4-mm diameter) unless the stream gradient was sufficiently high to flush sediment from storage. One-half of the debris dams broke up or were newly formed over a 3-year period, which suggests that they usually released sediment and woody debris before the pools they formed were filled with sediment. Woody debris removal decreased debris-covered area, debris dam frequency, and hydraulic friction in some cases but, in others, these variables were unaffected or recovered within 2 years after erosion and adjustment of the streambed. No consistent differences in pool dimensions were found between treated and untreated clear-cut reaches. Comparisons of habitat in forested and clear-cut streams suggested that removing debris from clear-cut streams reduced salmonid carrying capacity. Retention and natural reformation of debris dams in cleared reaches prevented the expected deterioration of habitat. However, the removal and destabilization of existing woody debris may cause depletion of debris before riparian trees can regrow and furnish new material to the clear-cut streams.

Surface Morphology in the Ablation Area of the Khumbu Glacier

The surface morphology of the ablation area of the Khumbu Glacier in east Nepal was surveyed and the details were mapped. The ablation area includes a bare ice area as well as a debris-covered area. Of the complex surface morphologies, large debris-covered cones, large hollows, and irregular uneven surfaces can be identified. The irregular uneven surfaces are subdivided into eleven morphological units according to the morphological elements such as relative relief, directional features of ridges, and distribution of ice cliffs, lakes, and streams. The surface morphology change both in transverse and in longitudinal direction of the glacier.The distribution of 5 morphological elements, relative relief, directional feature of ridges, exposure of glacier ice including ice cliffs, lakes, and streams are shown. According to combine these morphological elements, a morphological classification is obtained. The large debris-covered cones, large hollows, and irregular uneven surface can be classified. The surface morphology change both in the transverse and longitudinal direction on the glacier. The summary of the longitudinal change of the morphology and the units is;(i) The wide bare ice area in the upper section of the ablation area between 7 km and 10 km from the terminus is a row-relief gentle morphology with the micro unevenness such as ice pinnacles (Units 10, 11, 3, 7).(ii) In the section between 7 km and 4.5 km from the terminus, the relative relief increases and streams with high ice cliffs are found (Units 3, 7, 5).(iii) In the section 4.5 km to 2 km upglacier from the terminus which includes the 2nd area, the relief attains the maximum and the morphology becomes very complicated. Many ice cliffs, lakes, and streams are located (Units 6, 8, 9).(iv) The terminal 2 km shows the relatively moderate relief with thick debris-mantle (Units 5, 4, 2, 1).