Land Degradation in the Parwan Valley

S.C. Boucher
School of Geography and Environmental Science
Monash University, Victoria 3800

The Parwan Creek valley is located near Glenmore in the north-west of the region and contains some of the most severe sites of water erosion in Victoria. The Parwan Hydrological Experimental Area was established in 1953 by the Soil Conservation Authority and forms part of the White Elephant Reserve (Hartland and Papworth 1995). Extensive, deep tunnel erosion was recognized by Hexter et al. (1956) as the main problem on the White Elephant Hill.

Gully erosion in Parwan Valley.

Diagram: Prediction of dispersive potential for soils affected by tunnel erosion

Prediction of dispersive potential for soils affected by tunnel erosion in the Parwan Experimental Area (after Fitzpatrick et al. 1994).

The average annual precipitation of 508 mm was shown to be highly variable over 28 years of records and average monthly rainfall was highest in April-May and August-November (Wu

et al.

1986).

Hexter

et al

. (1956) noted that prior to European settlement, the area was covered by

Eucalyptus

spp. trees and thick stands of native grasses. Clearing took place to improve the growth of the grasses that were overgrazed by cattle, rabbits and sheep. Landslides were known to have increased in number after the inherently delicate environmental balance was upset by the above-mentioned activities.

Tunnelling appears to have started by direct contact of surface water with the subsoil following extensive sheet erosion and/or along rotted tree stump roots. All tunnels debouched onto the hillslopes rather than the tributary gully wall, thus being of the "continuous gradient" form, and the greatest sinkhole depth reported in Victoria (i.e. 7.6 m) was recorded at this site (Boucher 1990)

The subsurface (A2) and subsoil (B) horizon samples proved to be dispersive (SC Boucher and P Rengasamy unpublished data).

Physico-chemical soil data from the severely tunnelled White Elephant Ridge in the Parwan Valley Experimental Area indicated that the material was ‘potentially dispersive’ when applied to the scheme proposed by Rengasamy et al. (1984). From available soil data (Wu et al. 1986; SC Boucher, unpublished data), the profiles were classified as varying between a Red Sodosol, Red Kurosol and Red Chromosol in the Australian Soil Classification of Isbell (1996) (DB Rees pers. comm). In terms of land-use, this ridge was grouped by Hexter et al. (1956) as being in ‘Class 5’, the definition being presented below.

Land suitable for strictly controlled grazing where no erosion control measures or pasture improvement can be undertaken, except where special means of top-dressing are adopted, e.g., by aircraft or blower (Hexter et al. 1956, 24).

Diagram: The relation between ESP and Exchangeable Mg/C

The relation between ESP and Exchangeable Mg/Ca for soils affected by tunnel erosion in the Parwan Experimental Area (after Fitzpatrick et al. 1994).

The level of sodicity varied considerably between profiles with the range of ESP for surface and subsurface soils being 1.0 - 7.1 and 1.4 - 8.9 respectively (Ford et al. 1993). The Exchangeable Mg/Ca values were 0.7 - 4.4 in the surface soils and 2.4 - 18.0 in the subsurface horizons (Ford et al. 1993).

The ratios ranged between 0.7 - 4.4 for surface soils and 2.4 - 18.0 for subsurface material (Ford et al. 1993).

An important technique in land management has been rabbit control, as the animals inhabit tunnels (Hartland and Papworth 1995, Anon. 1997).

The Parwan Valley near Glenmore. This area has a high
incidence of various forms of land degradation - including
landslips, tunnel and gully erosion.

References

Anon. (1997). Parwan Valley rabbit control is no white elephant. Trees and Natural Resources 39, 26.

Fitzpatrick RW, Boucher SC, Naidu R, Fritsch E (1994) Environmental consequences of soil sodicity. Australian Journal of Soil Research 32, 1069-1093.

Ford GW, Martin JJ, Rengasamy P, Boucher SC, Ellington A (1993) Soil sodicity in Victoria. Australian Journal of Soil Research 31, 869-909.

Hartland R and Papworth MP (1995) `Rabbit control in the Parwan Valley and its value for catchment management'. Centre for Land Protection Research Technical Report No. 26. (Land and Catchment Protection Branch, Department of Conservation and Natural Resources: Heidelberg)

Hexter GW, Leslie TI, Pels S (1956) `A land-use class survey of the Parwan Valley, Victoria'. (Soil Conservation Authority of Victoria) (Government Printer: Melbourne)

Isbell RF (1996) `The Australian soil classification'. (CSIRO Australia: Collingwood)

Rees DB pers. comm. Keith Turnbull Research Institute, Department of Natural Resources and Environment, Frankston, Victoria 3199.

Rengasamy P, Greene RSB, Ford GW, Mehanni AH (1984) Identification of dispersive behaviour and the management of Red-brown Earths. Australian Journal of Soil Research 22, 413-431.

Wu AYK, Hartland R, Papworth M (1986) `Parwan Hydrological Experimental Area'. (Land Protection Division, Department of Conservation and Lands: Kew)

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