Title

Performance of grass and eucalyptus riparian buffers in a pasture catchment, Western Australia, part 1: riparian hydrology

Document Type

Article

Publication Date

2006

Journal Title

Hydrological Processes

Keywords

riparian hydrology, subsurface flow, surface flow, riparian buffer, nutrient, phosphorus

Abstract

Rainfall takes many flowpaths to reach a stream. and the success of riparian buffers in Water quality management is significantly influenced by riparian hydrology. This paper presents results from hydrometric monitoring of riparian buffer hydrology in a pasture catchment. Runoff processes and riparian flowpaths were investigated on two planar hillslopes with regenerating grass and E. globulus buffers. Surface runoff and subsurface flows (A- and B-horizons) were measured for 3 years using surface runoff collectors. subsurface troughs and piezometers. Water volumes moving through the riparian buffers via the measured flowpaths Were ranked B-horizon >> surface runoff approximate to A-horizon. Runoff volumes through the B-horizon troughs were an order of magnitude greater than those recorded for the most productive surface runoff plots or the A-horizon troughs. Subsurface runoff and saturation-excess overland flow (SOF) were limited to the winter months, whereas infiltration-excess overland flow (IEOF) can Occur all year round during intense storms. Surface runoff was recorded on 33 occasions, mostly during winter (late May-early October). and total annual Surface runoff volumes collected by the 20 unconfined (2 in wide) runoff plots varied between > 80 and < 20 m(3). Subsurface flow only occurred in winter, and the 6 m wide B-horizon Subsurface troughs flowed above 11 s(-1) continuously. whereas the A-horizon troughs flowed infrequently (< 6 days per year). In summer, surface runoff occurred as IEOF during intense storms in the E. globulus buffer, but not in the grass buffer. Observations suggest that surface crusting reduced the soil's infiltration capacity in the E. globulus buffer. During winter, SOF and seepage were observed in both buffers, but subsurface flow through the B-horizon was the dominant flowpath. Key hydrologic differences between the grass and tree buffers are the generation of IEOF in the E. globulus buffer during intense summer storms. and the smaller subsurface runoff Volumes and fewer flow days in the E. globulus buffer. Low Surface runoff volumes are likely to limit the potential of these buffers to filter pollutants front Surface runoff. High subsurface flow volumes and saturated conductivities are also likely to limit the residence time of water in the subsurface domain. Based on their hydrologic performance, the key roles of riparian buffers in this landscape are likely to be displacing sediment and nutrient-generating activities away from streams and stabilizing channel morphology. Copyright (c) 2006 John Wiley & Sons, Ltd. [References: 61]