2.1 Location 2.2 Climate 2. OVERVIEW of the ROPER RIVER CATCHMENT
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2 Overview of the Roper River Catchment 2. OVERVIEW OF THE ROPER RIVER CATCHMENT 2.1 Location 2.2 Climate The study area includes the catchment of the Roper River and its tributaries (refer Map 2). The The study area is located within the monsoonal Roper River is a large, perennial flowing river and tropics. The dominant feature of the north-west has a catchment area of 81,794 km2, which is one monsoon is the occurrence of two distinct of the largest river catchment areas in the seasons, an almost rainless dry season from May Katherine region. The study area is drained by ten to September, and a wet season from November rivers and three major creeks, some of which are to March. April and October are transitional also perennial: the Roper, Phelp, Hodgson, months. (Woodroffe et al., 1986). Arnold, Wilton, Mainoru, Jalboi, Strangways, Chambers and Waterhouse Rivers, and Maiwok, Table 2.1 summarises climate details for the Flying Fox and Elsey Creeks. following locations in the Roper River catchment: Daly Waters, Larrimah, Ngukurr and Flying Fox The Roper River starts as Roper Creek (also Station. In addition to the four locations called Little Roper River) and becomes the Roper summarised in Table 2.1, the mean annual rainfall River downstream of Waterhouse River junction recorded for Mataranka Homestead Resort, near Mataranka. The Elsey Creek system drains Nutwood Downs, Mainoru and Maranboy is 792.6 the large Sturt Plateau region, which is located in mm, 694.2 mm, 747.3 mm and 823.3 mm the south-western section of the catchment. The respectively (NT Bureau of Meteorology, 2000). Arnhem Land Plateau, rising up to 440m, and the Wilton River Plateau are located in the northern Over 90% of the mean annual rainfall throughout section of the catchment, and consist the Roper River catchment falls during the wet predominantly of Kombolgie sandstone. The season (November to March). The mean monthly middle section of Roper River consists of a very rainfall varies from 0 mm during the dry season to braided river channel. The Roper River flows 216.2 mm during the wetter months. Figures 2.1 generally in an easterly direction, although the and 2.2 show the mean monthly rainfall recorded geology of the catchment influences the direction for Mataranka Homestead Resort and Ngukurr. of the drainage systems. The normal tidal limit of the Roper River is at Roper Bar Crossing (shown on Map 2). From this crossing, the Roper River 250 traverses the alluvial coastal plain eastward for 200 145km before entering the Gulf of Carpentaria. 150 There are currently no large surface water storages on the Roper River or its tributaries. 100 Rainfall (mm) 50 Within the Roper River catchment there are several small towns and communities, of which 0 JFMAMJJASOND Mataranka is the regional centre. Others towns Month and communities include: Barunga, Beswick, Bulman, Daly Waters, Larrimah, Hodgson Downs, Figure 2.1 Mean Monthly Rainfall for Mataranka Roper Bar and Ngukurr. Homestead Resort (1916 - 1999) 200 150 100 Rainfall (mm) 50 0 JFMAMJJASOND Month Aerial View of Roper Bar Crossing (May 1999) Figure 2.2 Mean Monthly Rainfall for Ngukurr (1910 - 1999) Top End Waterways Project ROPER RIVER CATCHMENT 3 Overview of the Roper River Catchment Table 2.1 Summary of Climate Data for Locations within the Roper River Catchment Daly Waters Larrimah Ngukurr Flying Fox Stn (1873 - present) (1952 - present) (1910 – present) (1996 – present) Mean Daily Min-Max Temp. Range (oC) 19.1 – 34.2 19.8 - 34.0 20.8 – 34.2 20.3 – 34.9 Mean 9am Relative Humidity (%) 54.4 62.0 65.8 64.1 Mean 3pm Relative 30.6 35.4 35.3 39.5 Humidity (%) Mean Annual Rainfall 669.2 [101] 805.3 [45] 752.4 [55] 992.7 [3] (mm) [No. years] Mean Monthly Rainfall 1.6 – 163.0 0.3 – 198.8 0.4 – 172.5 0 – 216.2 Range (mm) (July - Feb) (Aug - Jan) (Aug – Jan) (Aug - Feb) Highest Recorded 180.1 408.6 271.5 117.1 Daily Rain (mm) (Nov 1896) (Jan 1987) (Jan 1976) (Feb 2001) Mean Number of Rain Days per Year 56.4 66.7 51.4 74.8 Mean Total Annual 2,405.5 - 2,219.2 1,523.3 Evaporation (mm) Source: Climate and Consultancy Section, NT Bureau of Meteorology (2000-2001) Throughout the Roper River catchment mean 1500 o o monthly temperatures range from 19.1 C to 34.9 C 1400 1300 (Table 2.1). The lowest temperature recorded for 1200 o these four stations was 0.6 C whilst the highest 1100 o 1000 temperature recorded was 44 C. Relative humidity 900 varies daily and seasonally. Dry season (May – 800 700 September) relative humidity averages range from 600 500 43.4 - 68.2 per cent at 9am and 20.6 - 34.7 per Total Annual Rainfall (mm) 400 cent at 3pm. Whilst wet season (November to 300 March) relative humidity averages range from 51.6 200 100 - 83 per cent at 9am to 25.7 - 62.5 at 3pm. 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 Year The average yearly evaporation greatly exceeds Figure 2.3 Total Annual Rainfall for Larrimah the average rainfall, which is typical for the (1953 – 1999) northern Australian climate (Sivertsen and Day, 1985). Lucas and Manning (1989) reported that 1600 evaporation exceeds rainfall for nine months of the 1500 1400 year at Mataranka and peaks at the start of the 1300 1200 build up season (October and November). 1100 1000 900 Figures 2.3 and 2.4 show the total annual rainfall 800 recorded for Larrimah (1953-1999) and Nutwood 700 600 Downs (1936-1999) respectively. Rain is usually Total Annual Rainfall (mm) 500 400 high-intensity falls. Most of the region’s rain 300 comes as hard, intermittent, tropical showers, 200 100 oftern associated with thunder and lightning 0 1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 (Bauer, 1964) or as monsoon troughs and tropical Year lows, which are often the remains of cyclonic Figure 2.4 Total Annual Rainfall for Nutwood depressions. Downs (1936-1999) Top End Waterways Project ROPER RIVER CATCHMENT 4 Overview of the Roper River Catchment 2.3 Geomorphology and can be described in terms of its component parts, Landform which are land units. Each unit, while generally representing a uniform assemblage of data on Surveys providing detailed land systems, land unit topography, soils and vegetation, also describes or soils mapping have been carried out for areas the potential or capability of the land represented throughout the Roper River catchment. Figure 2.5 (Aldrick and Robinson, 1972). shows the location and reference details of these surveys. Map 3 shows the predominant landforms A total of 62 land systems were mapped and throughout the Roper River Catchment. This map described as part of the ‘Land Systems of the is based on the Northern Territory Soil Survey Roper River Catchment, Northern Territory’ survey mapping at a scale of 1:2,000,000 (Northcote, (Aldrick and Wilson, 1992). These land systems 1968) which has been used because it is the only have been grouped into six “geomorphic survey that covers the entire Roper River provinces” which are summarised in Table 2.2. catchment. The soil survey information has been These geomorphic provinces provide a basis for re-grouped according to landform. Within the predicting the susceptibility of land to degradation Roper River catchment there were six major (Aldrick and Wilson, 1992). landforms identified ranging from plateau surfaces; plateau escarpments; gorges and ridges The Sturt Plateau, covering the south-western associated with the dissected plateau and hills; section of Roper River catchment, has been plains; drainage lines, associated floodplains and described as an old uplifted erosion surface of billabongs; salt pans and tidal flats. some 250m elevation. It is a flat to gently undulating plain that is deeply weathered, covered The Arnhem Land Plateau, dominated by by thick laterite and associated soils and supports Kombolgie sandstone, rises up to 440m above sea predominantly savannah vegetation (Day et al., level. Other plateaus include Wilton River Plateau 1985). A total of 19 land systems were mapped and the Sturt Plateau. and described as part of the ‘Land Resources of the Sturt Plateau’ survey (Day et al.,1985); eight of Land systems mapping is based on recurring these land systems comprise gently sloping to patterns of topography, soils and vegetation almost level plains and four comprise alluvial (Christian and Stewart, 1952). Each land system plains on the Sturt Plateau. viqixh gthment2foundry vexh2iw 9vnd2ystems2of2the2oper2iver2gthment9 IXPSHDHHH2@eldrik282ilsonD2IWWPA 9vnd2esoures2of2the2turt2lteu2E2 e2eonnissne2vnd2ystem2urvey9 IXPSHDHHH2@hy2et2lFD2IWVSA 9he2vnd2ystems2of2tF2idgeon2ttion9 IXPSHDHHH2@pogrtyD2IWVQA vexh2 xs 9vnd2esoures2of2ilsey2rkD2wtrnk9 IXPSDHHH2@vus282wnningD2IWVWA 9he2vnd2 nits2of2yworrie2ttion9 IXSHDHHH2@vynh282wnningD2IWVTA 9vnd2esoures2of2undy2greek2hevelopment2ere9 IXSHDHHH2@hy282rendersonD2IWVSA ysv 9oils2of2the2 pper2oper2linsD2worok2ttion9 IXPHDHHH2@hy282oodD2IWUTA 9etls2of2eustrlin2oilsD2xorthern2rt2of2the xorthern2erritory9 IXPDHHHDHHH2@xorthoteD2IWTVA x H SH IHH ISH usvywii Figure 2.5 Location and Reference Details for Land System, Land Unit and Soil Mapping Surveys Conducted throughout the Roper River Catchment Top End Waterways Project ROPER RIVER CATCHMENT 5 Overview of the Roper River Catchment Table 2.2 Major Geomorphological Provinces within the Roper River Catchment (Adapted from Aldrick and Wilson, 1992) Geomorphic General Topography and Rate of Natural Erosion Major Vegetation Communities Province Main Characteristics of the and Soils Geomorphic Province G1 Very low relief. Gently Very slow (erosionally stable; little Mid-high open woodland. Ferruginous lithosols, undulating plains and rises. sediment produced due to very lateritic podzolics, red and yellow earths, earthy Intact areas of mature low relief; permeable soils; and sands and brown clays. laterite on old, stable erosion very old, stable drainage network) surfaces. G2 High relief.