The Tarrawarra Catchment is located in southern Victoria, Australia (37°39' south, 145°26' east). The climate is temperate with a mean annual rainfall of 820 mm and a potential evapotranspiration of 830 mm [Bureau of Meteorology, 1988]. The maximum mean monthly rainfall occurs in October and the minimum occurs in January [Land Conservation Council of Victoria, 1973]. Maximum potential evaporation occurs in summer. Mean summer minimum and maximum temperatures are 9° and 24° respectively and average winter minimum and maximum temperatures are 3° and 10° respectively [Bureau of Meteorology, 1988]. Compared with evapotranspiration, there is a significant rainfall deficit in summer, while in winter there is a significant rainfall excess. Winter storms typically result from cold fronts and synoptic scale depressions while summer storms are predominantly frontal and convective. The respective six minute, one hour and one day rainfall intensities are 49 mm/hr, 16 mm/hr and 2.4 mm/hr for a one year average recurrence interval storm and 100 mm/hr, 30 mm/hr and 4.3 mm/hr for a ten year average recurrence interval storm.
Tarrawarra is underlain by the Humevale formation which consists of siltstone
with interbedded thin sandstone and local bedded limestone lenses and is
from the lower Devonian period [Garratt and Spencer-Jones, 1981]. The soils
in the Tarrawarra catchment consist of three units. On the upper slopes is
a texture contrast soil with a loam-clay loam A horizon (15-25 cm deep) and
a heavy yellow-grey clay B horizon. The midslope soils have a loam-clay loam
A horizon (15-30 cm deep) with a silty B1 horizon and a silty-clay B2 horizon.
The soils in the depressions have a deeper 25-40 cm silty A horizon, and
a silty B horizon. Parts of the catchment, particularly the upper slopes,
have a bleached A2 horizon. The depth of unconsolidated sediments varies
from 40 cm at some points on or near the ridge-tops to in excess of 2 m in
the depressions. Small amounts of ironstone gravel are present in the profile,
particularly in the A2 horizon on the upper slopes and ridge-tops. Perched
water tables form in the A horizon during the wetter months of the year.
The surface soils crack during dry periods. A detailed description of the
available soils data is provided later.
The local terrain is undulating and has an elevation of approximately 100 mAHD
(Australian Height Datum). In the catchment, hillslopes vary from strongly
convergent through to divergent and the aspect ranges from east through south
to north-west (Figure 1). The maximum relief is 27 m and the hillslopes typically
have slopes of 11-14%. The main drainage line has a slope of 4%. There are
no channels within the catchment. The catchment area is 10.8 ha and the land
is used for dryland grazing of dairy cows. It has perennial (improved) pastures
and is divided into four main paddocks. Wind breaks exist along two-thirds
of the northern boundary (10 m Cypress trees) and a small part of the southern
boundary (5 m mixed Australian native trees) and there are two Eucalyptus
sp. trees located in the south eastern corner of the catchment (Figure 1).
A sealed road follows the northern boundary of the catchment and an access
laneway follows the southern boundary (Figure 1). Runoff from the road does
not flow into the catchment. The fate of runoff from the access laneway is
described later.
We believe that the Tarrawarra catchment is representative of landscapes
with relatively shallow soils of low to moderately high lateral permeability
with an impeding layer at depth, for which topography plays a significant
role in routing water through the landscape, and for climates ranging from
temperate to subhumid. These conditions apply over large parts of south-eastern
Australia and in many other parts of the world.
Bureau
of Meteorology, Climatic Atlas of Australia, pp., Australian Government
Printing Service, 1988.
Garratt, M. J. and Spencer-Jones, D., 1981. Yan Yean Geological Map, Geological
Survey of Victoria, Melbourne.
Land Conservation Council of Victoria, Report on the Melbourne study
area, 444 pp., Land Conservation Council of Victoria, Melbourne, 1973.
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