2 Overview of the Daly River Catchment 2. OVERVIEW OF THE DALY RIVER CATCHMENT 2.1 Location 2.2 Climate The study area includes the catchment of the Daly The study area is located within the monsoonal River and its tributaries (refer Map 2). The Daly tropics. The dominant feature of the north-west River is one of the Northern Territory’s largest monsoon is the occurrence of two distinct 2 rivers, having a catchment area of 52,577 km , and seasons, an almost rainless dry season from May is one of a relatively few to have a perennial flow to September, and a wet season from November (Morrison, 1970). The main tributary of the Daly to March. April and October are transitional River is the Katherine River. Other important months. (Woodroffe et al., 1986). Table 2.1 tributaries are the Flora, Fergusson, Edith and summarises climate details for several locations Douglas Rivers. The King and Dry Rivers have within the Daly River catchment. large catchments but are in a lower rainfall area and contribute nothing to the dry season flow of Over 90% of the rainfall at Mango Farm (Daly the Daly. (Morrison, 1970). Map 2 shows the River), Douglas River, Pine Creek and Katherine tidal, permanent (or perennial) flowing and dry (or falls during the wet season (November to March). ephemeral) sections of the rivers and creeks within Rain is usually high-intensity falls. Most of the the Daly River catchment. region’s rain comes as hard, intermittent, tropical showers, often associated with thunder and The Katherine River headwaters are formed in the lightning (Bauer, 1964) or as monsoon troughs and high relief sandstone escarpment country of the tropical lows, which are often the remains of Arnhem Land Plateau approximately 150km cyclonic depressions. Intensity of rainfall is upstream of Katherine. The river drops down from important in relation to rate of runoff and soil the escarpment through a series of sandstone erosion. The normal falls are quite sufficient to gorges, which make up the Katherine Gorge, cause local flooding and erosion. before reaching the lowlands upstream of Katherine. Approximately 60km west of Katherine, The highest recorded daily rainfall at Mango Farm the Katherine and Flora Rivers join to become the (Daly River), Douglas River and Katherine is Daly River, which continues westward for 354km 218.5mm, 206.4mm and 128.5mm, respectively before entering the Timor Sea at Anson Bay. (NT Bureau of Meteorology, 1997). Figures 2.1 and 2.2 shows the mean monthly rainfall for The main valley of the Daly River is a broad Katherine and Mango Farm at Daly River. undulating area bounded by low ranges on the south-west or north-east. After the incised passage through the Rock Candy and Mt Nancar 300 ranges, the Daly River traverses a predominantly alluvial coastal plain for some 99km, and is under 200 tidal influence for this distance. The normal tidal 100 limit is at Daly River Crossing (shown on Map 2). 0 Rainfall (mm) JFMAMJJASOND Within the Daly River catchment there are several Month towns, of which Katherine is the regional centre. Others include Pine Creek and Daly River. Figure 2.1 Mean Monthly Rainfall for Katherine There are two weirs along the Katherine River (1942-1997) located upstream of Katherine at Knott’s Crossing and Donkey Camp Pool (refer Map 2). Knott’s Crossing weir is a concreted rock fill wall that was 400 constructed in the 1960’s, raising the water level 300 by approximately 1.5m. Donkey Camp weir, which 200 was commissioned in 1983, is located on a natural rock bar and is used to increase water storage for 100 Rainfall (mm) the supply of water to Katherine township. 0 JFMAMJJASOND There are currently no large surface water Month storages on the Daly River or its tributaries, although possible future sites have been identified. Figure 2.2 Mean Monthly Rainfall for Mango Farm at Daly River (1980-1997) Top End Waterways Project DALY RIVER CATCHMENT 3 Overview of the Daly River Catchment At Mango Farm (Daly River) the average yearly Mean monthly temperatures range from 19.8oC – evaporation of 2,418.0 mm greatly exceeds the 34.4oC. Relative humidity varies daily and average rainfall (1,308.4 mm), which is typical for seasonally. Dry season (May-September) relative the northern Australian climate (Sivertsen and humidity averages range from 58.4–62.2 percent Day, 1985). Figures 2.3 and 2.4 show the total at 9am and 28.4-32.2 percent at 3pm. Whilst wet annual rainfall for Katherine (1873-1998) and season (November to March) relative humidity Mango Farm at Daly River (1980-1998), averages range from 75.6-84.2 percent at 9am respectively. and 46.6-58.6 percent at 3pm. Table 2.1 Summary of Climate Data for Locations within the Daly River Catchment Katherine Pine Creek Douglas River (Douglas- Mango Farm Daly Research Stn) (Daly River) Mean Daily Min-Max o 20.4 – 34.3 20.1 – 34.1 19.8 – 34.4 20.4 – 34.1 Temp. Range ( C) Mean 9am Relative 66.0 63.6 71.0 73.0 Humidity (%) Mean 3pm Relative 37.0 36.2 39.0 43.0 Humidity (%) Mean Annual Rainfall 1,009.3 1,147.6 1,157.4 1,308.4 (mm) Mean Monthly Rainfall 0.1 – 245.9 1.2 – 272.0 0.5 – 271.0 0.3 – 326.2 Range (mm) (June – Feb) (Aug – Jan) (Aug – Jan) (June – Feb) Highest Recorded Daily Rain (mm) 128.5 - 206.4 218.5 Mean Number of Rain Days 79.8 74.7 82.3 95.3 Mean Annual Evaporation (mm) - - 2,418.0 Source: Climate and Consultancy Section, NT Bureau of Meteorology (1997) 2000 1800 1600 Total 1400 Annual 1200 Rainfall 1000 (mm) 800 600 400 200 0 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Year Figure 2.3 Total Annual Rainfall for Katherine (1873-1998) Top End Waterways Project DALY RIVER CATCHMENT 4 Overview of the Daly River Catchment Total 2000 Annual 1600 Figure 2.4 Rainfall 1200 800 Total Annual Rainfall (mm) 400 for Mango Farm at 0 Daly River (1980- 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 1998) Year 2.3 Geomorphology and Land units have also been described for the Daly Landform River Agricultural Area (Fogarty and Gibbs, 1976); areas around Katherine; and several pastoral properties including Mathison Creek, Elizabeth Surveys providing detailed land systems or land Downs, Manbulloo, Dorisvale and Litchfield unit mapping have been carried out for areas Stations. throughout the Daly River catchment. There is no one survey that covers the entire Daly River The geology of the Daly River catchment has been catchment. Land systems mapping is based on mapped (at 1:100,000 and 1:250,000) and recurring patterns of topography, soils and described by the Department of Mines and Energy. vegetation (Christian & Stewart, 1952). Each land The geology, geomorphology and land resources system can be described in terms of its component of the Katherine Gorge National Park have also parts, which are land units. Each unit, while been described and mapped by Baker and Pickup generally representing a uniform assemblage of (1987), Mulder and Whitehead (1988) and data on topography, soils and vegetation, also Sivertsen and Day (1985). describes the potential or capability of the land represented (Aldrick & Robinson, 1972). Map 3 shows the predominant landforms throughout the Daly River Catchment. This map is The first systematic study of the land systems (at a based on the Northern Territory Soil Survey scale of 1:500,000) of the Katherine-Darwin region mapping at a scale of 1:2,000,000 (Northcote, was completed by Christian and Stewart (1952), 1968) but has been re-grouped according to ‘General Report on Survey of Katherine-Darwin landform. Within the catchment, landforms vary Region, 1946’. The survey was of a broad from high relief sandstone escarpment country in reconnaissance nature and covered areas along south-western Arnhem Land to an extensive level the Daly, Douglas, Fergusson, Flora and Katherine floodplain system, extending up to five kilometres Rivers. Five geomorphological units were from the river banks, along the lower sections of distinguished within this area and are summarised the Daly River. in Table 2.2. The Arnhem Land Plateau is a rugged sandstone The report of the Katherine-Darwin region formation (Kombolgie Sandstone) rising up to (Christian and Stewart, 1952) described 18 land 370m above sea level. This plateau is extensively systems and recommended further investigation faulted and dissected forming narrow, steep-sided into three due to the possibilities of economic crop gorge systems which are commonly 60m deep, production under natural rainfall conditions. The and are incised along joint sets trending north-east Tipperary land system, which lies within the Daly and north-west; and waterfalls from hanging River Catchment, was one of these three systems tributary valleys. Katherine Gorge is one such and a more detailed survey was carried out in feature, with a prominent north-easterly orientation 1961 by Speck et al (1965), ‘General Report on (Baker and Pickup, 1987; Kruse et al., 1994). Lands of the Tipperary Area, Northern Territory, There are 15 gorges covering a distance of 15 km, 1961’. Aldrick and Robinson have described the with cliff faces between 50 to 90 metres in height. land units for part of the ‘Tipperary area’ at a larger Other mountain ranges within the catchment scale of 1:50,000 in ‘Report on the Land Units of include Rock Candy Range, Mt Nancar Range and the Katherine-Douglas Area’ (1972).