Hydrologic processes and peak discharge response to forest removal, regrowth, and roads in 10 small experimental basins, Western Cascades, Oregon

Abstract

Abstract. The magnitude, seasonality, and duration of peak discharge responses to forest removal and regrowth and roads in 10 pairs of experimental basins in the western Cascade Range of Oregon are consistent with fundamental water balance and routing concepts in hydrology. Hypothesized effects of forestry treatments on evapotranspiration, cloud water interception, snowpack dynamics, and subsurface flow interception vary predictably by season, geographic setting, amount of forest canopy removal, stage of canopy regrowth, and arrangement of roads in the basin. Posttreatment responses of selected subpopulations of matched peak discharge events were examined over 10-to 34-year posttreatment periods in treated-control basin pairs in a range of geographic settings. Changes in evapotranspiration associated with forest canopy removal and regrowth apparently accounted for significant increases (31-116%) in peak discharges during the first postharvest decade in 8 of 10 treated basins, but the events that were affected were small (<0.22-or 0.28-year return periods) and occurred in the fall (September-November), when soils are in moisture deficit, rather than in spring (March-May), when soils are in moisture surplus. For a given amount of forest canopy removal, initial increases in small, fall events were greater in drier basins than wetter basins, and increases tended to disappear as forest canopies regrew. Changes in cloud water interception apparently offset changes in evapotranspiration in two partially cut basins. Changes in snowpack dynamics apparently accounted for significant increases (25-31%) in winter rain-on-snow events, but other types of winter events did not change, in four of five basins at the H. J. Andrews Experimental Forest. Changes in subsurface flow interception apparently accounted for significant increases (13-36%) in large (>l-year return period) events in seven of eight basins with roads, and, controlling for geographic location, the magnitude of increases was related to the density of midslope roads.

At what scales do climate variability and land cover change impact on flooding and low flows?

“…Relevant publications include Lall (2005), Pittock (2002), Trenberth (1999), Benestad (2003), Beniston et al (1997), Hanson et al (2004), Svensson et al (2005), Hisdal et al (2001), and Llasat et al (2005). Similarly, there have been numerous publications on land cover change effects on floods, low flows and, more generally water yield, including Robinson et al (2003), Brown et al (2005), Andréassian (2004), Cosandey et al (2005), Bonell and Bruijnzeel (2005), Bonell (1999), Mahé et al (2005b), Archer (2003), Jones (2000), Bronstert et al (2002) and Pfister et al (2004). Rodriguez-Iturbe (2000), Peterson et al (2000), Woods (2005) and Anderson et al (2005) provide perspective on hydrological variability and other background information highly relevant to the issue of scales of climate variability and land cover change impact on flooding and low flows.…”

Land-cover impacts on streamflow: a change-detection modelling approach that incorporates parameter uncertainty

“…HJA is also the location for much of the analysis from Jones & Grant (1996) and the papers that followed (Beschta et al, 2000;Jones & Grant, 2001;Thomas & Megahan, 1998;2001) debating the interpretation of results of statistical analyses of paired-catchment data. Detailed site descriptions of the overall HJA and the small basins can be found in Rothacher et al (1967), Jones & Grant (1996) and Jones (2000). Our study focuses on the small catchments WS1 (treatment, 0.96 km For each catchment a series of runoff peaks was derived.…”

An Assessment of the Impacts of Climate Change on the Upper Clackamas River Basin with a Distributed Hydrologic Model

“…Areas that have been logged show less evapotranspiration because of the loss of vegetation and greater overland flow because of soil compaction, both of which lead to higher peak, seasonal, and annual flows from a catchment (Harr et al 1979). Jones (2000) folUld that this effect on peak flows may diminish considerably and possible reverse itself as regrowth occurs.…”

“…Research has shown that the logging of the forests of western Oregon increase runoff, at least initially (Harr et al 1979;Jones 2000). Areas that have been logged show less evapotranspiration because of the loss of vegetation and greater overland flow because of soil compaction, both of which lead to higher peak, seasonal, and annual flows from a catchment (Harr et al 1979).…”

“…Runoff is dependent on a number of complex physical factors outside the scope of this analysis, and may be affected over time by changes in landscape characteristics such as forest removal and regrowth (Jones 2000). Table 3 shows a list of assumptions and processes that are not modeled.…”