Soil Conservation in Alpine Catchments

Extract from the Journal ofthe Soil Conservation Service of N.S. W., Volume 24, Number 2, April, 1968 SOIL CONSERVATION IN ALPINE CATCHMENTS BY D. P. CLOTHIER, H.D.A., SoiL CoNSERVATIONIST, CooMA AND R. W. CoNDON, B.Sc.AoR., SPECIAL SoiL CoNSERVATIONIST, SYDNEY G26535-1 SOIL CONSERVATION IN ALPINE CATCHMENTS BY D. P. CLOTHIER, H.D.A., Soil Conservationist, Cooma, and R. W. CoNDON, B.Sc.Agr., Special Soil Conservationist, Sydney HE stabilization of erosion in the highest reasonable condition as the inter-tussock T areas of the Australian Alps presents spaces have been occupied by herbaceous many problems not encountered in more ~pecies or covered with snowgrass foliage. favourable locations. Climatic conditions are Areas mapped as suffering from moder such that all treated areas need to be covered ate sheet erosion are generally similar in with straw mulch and tied down with net nature to those affected by minor sheet ero ting. This requires that some 4-5 tons of sion, but erosion has proceeded to the stage materials have to be taken to the site for where bare spaces have been enlarged, the each acre to be treated. In an area inacces intervening tussocks have died out ( Dur sible to normal wheeled vehicles, transport ham, 1959), exposing frequent bare erod of these materials and provisioning of the ing patches up to 1-2 chains in diameter, work force becomes a major problem. from which 1-6 inches of soil have been The Australian Alps which include the lost. The larger areas (more than 5 yards headwaters of the Snowy, Murray, and in diameter) need treatment to stabilize. Murrumbidgee river systems, comprise the Small bare areas may stabilize naturally if nation's major snow-fed catchments (figure the slope is reasonably flat (less than 10 per I). In a continent as dry as Australia, the cent) and some topsoil still remains. optimum development of the nation's re Severe sheet erosion represents the third sources 'vvill eventually be limited by the stage, where areas suffering from moderate availability of water and will require that sheet erosion have joined up to form large the limited area of snow-fed catchments be areas up to several acres extent, from which maintained in a stable condition (figure 2). as much as 2 feet of soil may be lost. The worst of this erosion is concentrated in the Detailed erosion surveys carried out by area between Carruthers' Peak and Mt the Soil Conservation Service (Greenup, Twynam, at elevations ranging from 6,500 1964) show that there are some r2,56o feet to 7,200 feet. In this locality, individual acres classified as minor sheet erosion ana areas of several acres have lost from 1 to I ,340 acres of moderate and severe sheet 2 feet of soil, exposing large rocks and erosion in the section of the Main Range boulders to form an erosion pavement between Dead Horse Gap on the Alpine (figure 3). Way and the Schlink's Pass Road. Erosion of this nature in such a harsh Minor sheet erosion in the alpine context environment constitutes a considerable is shown by small bare spaces between in threat to catchment stability. This article dividual tussocks of snowgrass (Poa caes describes the soil conservation measures car pitosa). Country in this condition will re ried out by the Soil Conservation Service generate naturally in the absence of grazing in the Carruthers' Peak-Mt Twynam area, animals. After 8 years of freedom frorn some 4- 5 miles north-northeast of Mt grazing, the country so affected is now in Kosciusko. 96 Soli Cotu~rvallon Journal :~'· ..···-:. '\, AREA AWAITING TREATMENT ('"··· .•./' ..:-~11 · .• · ·~~ "~..._ .... ....; ··' \ ....... : ·• PONOAGE}/·,r .·· ···--~-~-- ···· . , ... ut .. ·· ~<-'' " .,.... ....-· _.···· ...... ;' HtM RAMSMEAO ...... '"•, .•·· ...•..· ....· __..,..... .--~ .--··· SCA LE ..· ..-·· MILE. S 0 ,.·· ,•' ,..-·· .•' _..... SOl L CONSERVATION WORKS (..•'" KOSCIUSKO SUMMIT AREA •.,,...• Fig11re r.- P1an of the Kosciusko Summit Area showing location of stabilized areas near Carruthers' Peak and areas awaiting treat ment near Mt Twynam April, 1968 97 Figure 2.-The limited area of snow-fed catchments of the Australian Alps must be maintained in a stable condition to ensure optimum development of the nation's water resources Figure J.-Severe sheet erosion down to rocky pavement shows the small remnant of sub-soil with pedestalled plants struggling to survive-Mt Twynam 98 Soil CotUervatloA JouriUll TOPOGRAPHY Galeforce winds occur frequently on the ridges and saddles of the steep d-ivide be The term Kosciusko Massif has been tween the Geehi kiver on the west and the used to describe the general summit area Snowy River on the east. running northeast from Mt Kosciusko som~ 8--ro miles long by 3-4 miles wide. Viewed from. the. north a~d west the precipitous GEOLOGY AND SOILS terram g1ves the 1mpression of grandeur and massive mountains. vVhen approached The dark alpine humus soil is the main along the main road from the east the ter soil type in the area and occurs generally rain is plateau type \',;ith glacial cirques and to a depth of r-3 feet. These soils overlay well-.established drainage patterns from parent materials of granitic origin. A nar prevwus glaciations. Within this broad row belt of slate and schists runs roughly plateau area there is much steep country in north-northeast through the area from excess of 30• slope. Etheridge Range through Mt Lee and Car ruthers' Peak to Mt Twynam. CLIMATE VEGETATION Long-term meteorological records for the Carruthers' Peak area are not available. To an elevation of about 6,200 feet, the Records from the Spencer's Creek weather vegetation is a sub-alpine woodland domi station, operated by the Snowy Mountains nated by snow-gum (Eucalyptus nipho Hydro-Electric Authority at an elevation of phila), with a wide range of shrub species .),8oo feet, show annual precipitation rang forming an understorey on rocky moraine deposits or stony sites, with snowgrass (Poa ing from 6o to II I inches. The greater pro portion of this falls in the autumn winter caespitosa) on sites on which good soil de and spring as snow and sleet. Hi~h inten~ velopment has occurred. sity convectional summer storms are also Beyond Charlotte's Pass at 6,030 feet, the experienced as a result of east-moving air country is l~rgely treeless. The tall alpine masses being forced upward by the steep herb field. alliance of snowgrass and silver western escarpment. By extrapolating from snow da1sy ( C elmisia fongifolia) forms a the general relationship between elevation green and grey patchwork broken by and precipitation, annual precipitation at specialized communities such as heath-form Carruthers' Peak could be expected to range ing ~~rub~ in rocky shallow soils, bog com from to 130 inches. 90 mumttes. 1." groundwater areas, snow-patch Extreme daily temperature fluctuations commumhes at the base of snowdrifts, and are also experienced during the warmer part the "feldmark" communities of sparse, of the year. At Spencer's Creek, for the ground-hugging species on the windswept ten-~ear period 1956 to 1965, minimum and ridges and saddles of the Main Range. max1mum temperatures for January were The vegetation and soils have been de 24°F and 79°F. scribed in detail by Costin ( rgso), Taylor Under these climatic conditions the for ( 1957-58), and M orland 1958--59). mation of needle ice on bare, moist soils ~hroughout the spring, summer, and autumn EROSION 1s c?mmon. Pack snow, with frozen topsoil honzons and .surface vegetation, generally Prior t_o 1943 the area was open to sum occurs for penods of five to seven months mer grazmg by cattle and, although grazing each year, with snowdrifts persisting to Feb was banned on some ro,ooo acres around ruary and March in sheltered situations Mt Kosciusko from 1944, and from a further Following heavy snow seasons, as experi~ 54,290 acres in 1950. cattle were frequently enced in 1964, some snowdrifts carry seen on the slopes of Mt Kosciusko as late through into the following winter. as I957· April. 1968 99 In such an environment the balance of With the repeated removal of seedlings nature is very delicate. Disturbance of the and undermining of adjacent vegetation it is native vegetation by grazing and uprooting impossible for bared areas to stabilize of plants, by burning, and by trampling on naturally. Adjoining bared areas link up frequently sodden soils, has led to serious over areas of 5-10 yards square. Once bare er0sion of many areas. areas reach this size, down-cutting and undermining of adjacent non-eroded areas proceeds rapidly. Once the insulating effect of the pre viously stable vegetal cover is disturbed, There are now hundreds of acres from needle ice forms in the moist soil (figure which 2-3 feet of soil have been removed, 4). Dependent upon diurnal temperature exposing boulders and a stony sub-soil or fluctuations, and other factors such as soil erosion pavement (figure 5). When in moisture, this needle ice has the effect of dividual areas become large the concen lifting and pulverizing the bare soil surface trated run-off results in gullying which is to a depth of -! inch or more ( Costin, normally rare in alpine areas. 1950, and Durham, 1959.) As the ice The removal of such large quantities of needles thaw, the loosened soil rolls down soil by deep sheeting and gullying also re slope or is blown away by strong winds. sults in the burial of large patches of other Seedlings, which may establish themselves wise stable areas in situations downslope. during frost-free periods are wrenched out The old walking track, running along the and left lying on the pulverized surface. ridge of the divide from near Rawson's Pass The roots of established plants around the to Blue Lake and back to Charlotte's Pass, edge of the bared areas are undermined un has also become seriously eroded in many til the surface sod collapses, breaks off and sections where it has departed from the slides down the slopes.

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