CHANNEL NETWORK EXTENSION BY LOGGING ROADS IN TWO BASINS, WESTERN CASCADES, OREGON

CHANNEL NETWORK EXTENSION BY LOGGING ROADS IN TWO BASINS, WESTERN CASCADES, OREGON ABSTRACT: Based on field surveys and analysis of road networks using a geographic information system (GIS), we assessed the hydrologic integration of an extensive logging‐road network with the stream network in two adjacent 62 and 119 km2 basins in the western Cascades of Oregon. Detailed surveys of road drainage for 20 percent of the 350 km road network revealed two hydrologic flow paths that link roads to stream channels: roadside ditches draining to streams (35 percent of the 436 culverts examined), and roadside ditches draining to culverts with gullies incised below their outlets (23 percent of culverts). Gully incision is significantly more likely below culverts on steep (< 40 percent) slopes with longer than average contributing ditch length. Fifty‐seven percent of the surveyed road length is connected to the stream network by these surface flowpaths, increasing drainage density by 21 to 50 percent, depending on which road segments are assumed to be connected to streams. We propose a conceptual model to describe the hydrologic function of roads based on two effects: (1) a volumetric effect, increasing the volume of water available for quickflow and (2) a timing effect, altering flow‐routing efficiency through extensions to the drainage network. This study examines the second of these two effects. Future work must quantify discharge along road segments connected to the stream network in order to more fully explain road impacts on basin hydrology. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the American Water Resources Association Wiley

CHANNEL NETWORK EXTENSION BY LOGGING ROADS IN TWO BASINS, WESTERN CASCADES, OREGON

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Publisher
Wiley
Copyright
Copyright © 1996 Wiley Subscription Services, Inc., A Wiley Company
ISSN
1093-474X
eISSN
1752-1688
DOI
10.1111/j.1752-1688.1996.tb03490.x
Publisher site
See Article on Publisher Site

Abstract

ABSTRACT: Based on field surveys and analysis of road networks using a geographic information system (GIS), we assessed the hydrologic integration of an extensive logging‐road network with the stream network in two adjacent 62 and 119 km2 basins in the western Cascades of Oregon. Detailed surveys of road drainage for 20 percent of the 350 km road network revealed two hydrologic flow paths that link roads to stream channels: roadside ditches draining to streams (35 percent of the 436 culverts examined), and roadside ditches draining to culverts with gullies incised below their outlets (23 percent of culverts). Gully incision is significantly more likely below culverts on steep (< 40 percent) slopes with longer than average contributing ditch length. Fifty‐seven percent of the surveyed road length is connected to the stream network by these surface flowpaths, increasing drainage density by 21 to 50 percent, depending on which road segments are assumed to be connected to streams. We propose a conceptual model to describe the hydrologic function of roads based on two effects: (1) a volumetric effect, increasing the volume of water available for quickflow and (2) a timing effect, altering flow‐routing efficiency through extensions to the drainage network. This study examines the second of these two effects. Future work must quantify discharge along road segments connected to the stream network in order to more fully explain road impacts on basin hydrology.

Journal

Journal of the American Water Resources AssociationWiley

Published: Dec 1, 1996

References

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