STUDY CODE:    
 HF07 

ABSTRACTOR:    
 J. Jones and H. Hammond  
 

DATE: 
 Feb 11, 1998

KEYWORDS:     
 Streamflow, peak flow, disturbance, clear-cutting, roads
 

PARAMETERS:     
 Streamflow

AREA/REGION:    
 Western Cascades of Oregon  

STUDY PURPOSE/GOALS:       
 To quantify long-term changes in storm hydrograph behavior associated with
 clear-cutting and road construction, and to examine alternative hydrologic
 mechanisms to explain hydrograph changes in western Oregon.  

SITE CHARACTER:    
 The small basins are tributaries of Lookout Creek in the H.J. Andrews
 Experimental Forest near blue River, in the western Cascades of Oregon.
 Lookout Creek is one of the six large basins, all of which are within the
 Willamette National Forest.  The basins span elevations from 400 to 3200 m
 and have slopes of 60 to 100%.  Mean annual precipitation in the western
 Cascades ranges from 2300 mm at lower elevation to more than 2500 mm at  
 higher elevations.  Over 80% of precipitation falls from November to April,
 typically as rain below 400 m and as snow above 1200 m.  Elevations in
 between may alternatively receive snow or rain.  The study area is
 underlain by Tertiary and Quaternary volcanic rocks, primarily andesites
 and basalts, with some glacial deposits.  Soils are weakly developed with
 thick organic litter horizons, deeply weathered parent materials, and high
 stone content.  Before treatment, the vegetation of these basins consisted
 of mainly 100- to 500-year-old Douglas fir, western hemlock, and western
 red cedar in closed canopy stands, with increasing amounts of Pacific
 silver fir above 800 m.
 

METHODS:   
 34-year records from two pairs of experimental basins, ranging from 60 to
 101 ha, in the H.J. Andrews Experimental Forest were examined, as well as
 50-to-55 year records from three pairs of adjacent basins ranging from 60
 to 600 square km in the western Cascades.  The small basins were a paired
 basin experiment, with clearly defined pretreatment and post-treatment
 periods, two unreplicated treatments, and a control.  We examined changes
 in peak discharge between the treated and control basins for paired events,
 as a function of time before and after treatment.  The analytic approach
 for the large basins was more complicated.  No large basins in the western
 Cascades were unharvested thoughout this period, so no control basin was
 available.  Also, forest harvest treatments were imposed progressively
 though space and time.  However, the three pairs of large basins did have
 contrasting land use histories.  Therefore we were able to use the same
 response variable, that is, the difference in peak discharge for each
 paired event between the more harvested and less harvested basins, and we
 related this variable to the magnitude of the difference in harvest area
 between the basins.

COMMENTS:    
 Results published in:
   Jones, J.A. and G.E. Grant, Peak flow responses to clear-cutting and
 roads in small and large basins, western Cascades, Oregon.  Water Resources 
 Research, Vol. 32, No. 4, pp 959-974, April 1996.