77 Summary – Victoria River Catchment Very low and low diversity ratings were 6. SUMMARY – VICTORIA predominantly recorded in tidal sections where the RIVER CATCHMENT pools were very long and uniform. Sites with moderate channel type diversity had two habitat types, of which pools dominated the reaches. ♦ Reach Environs and Site Features ♦ Bank Condition and Stability Just over half the sites assessed were rated as having essentially natural reach environs, and the The majority of river banks throughout the remainder had some modification. Only one site catchment were considered stable, with a few (ie had moderate modification to the reach environs 10 sites) that had limited instability, and one site and no sites were assessed as having major or that was suffering from extensive instability due to extreme modification. Generally, the sites with stock and the presence of a vehicle crossing and essentially natural reach environs had relatively low track (Site 9_4 on Poison Creek). A subjective impact land uses, undisturbed vegetation and few assessment of bank stability conducted in the field local disturbances like grazing, infrastructure and indicated that the majority of sites recorded low concentration of animals at watering points. overall bank instability, however many sites had low to moderate and moderate bank instability, and Subjective disturbance ratings conducted in the some sites also had moderate to high and high field indicated that the majority of sites had low to levels of instability. very low levels of disturbance, and the remainder had low to moderate and moderate levels of Though most river banks were rated as being disturbance. One site was reported to have stable, some form of erosion processes were moderate to high level of disturbance due to the recorded at the majority of sites, and aggradation presence of an access track and people using the was recorded at one site. Only two sites were river reach for recreational activities. No sites were considered absolutely stable. Lower banks were highly, very highly or extremely disturbed. more stable than upper banks with an average of 94% of the lower bank considered stable, and 85% The majority of land adjacent to stream reaches considered stable for the upper bank. studied was under either freehold or leasehold tenure, including Aboriginal land. The major land The major factors affecting bank stability were high use recorded adjacent to the streams was grazing, flow and stock, and to a lesser extent, and to a much lesser extent, National Park. infrastructure (eg roads, tracks, crossings, bridges), Grazing activity, roads/tracks, river crossings, and floodplain scours, runoff and vermin. Smaller watering points for stock and feral animals were the contributing factors included tidal influence, people three major disturbances to stream reaches. tracks and clearing of vegetation. The only types of artificial bank protection measures recorded ♦ Channel Habitat Types, Diversity and were fencing along the river and/or at stock Dimensions watering points, which occurred at several sites, and gabions at one site. Reaches studied averaged 2,238m in length and ranged from 50-20,300m. Pools and riffles were ♦ Bed and Bar Condition and Stability the dominant habitat types located throughout the catchment. Pools generally occurred with riffles A subjective assessment of the overall bed stability and runs, and waterfalls were also associated with indicated that the majority of sites had stable river areas of steeper topography such as Limestone beds, while 13 sites recorded moderate bed Gorge and Cow Creek. There were only three aggradation and one site recorded bed erosion rapids recorded in the catchment, and one problems. cascade. The majority of survey work was conducted during the dry season so many rivers Moderate bed aggradation was located on Victoria and creeks were either completely dry or had River (5 sites), Bullo River (3 sites), Camfield River isolated pools. (3 sites), Jasper Creek and Gordon Creek. Most of the Victoria River and Bullo River sites were tidal, Channel type diversity assessed the number of and experience aggradation as sediments move different channel habitat types present and the through the estuary. Other sites, such as those on proportion of the reach occupied by pools versus Camfield River and Gordon Creek, had relatively other habitat types. The majority of sites recorded flat, uniform and shallow river beds with a large a high diversity of channel habitat types and these amount of sand and gravel. These sites were all mostly had two habitat types present. Sites with near stock watering points and vehicle crossings, very high diversity usually had three to four habitat and had bank erosion, floodplain scouring and new types, and were found in the steeper rocky sections channels forming. The site recording erosion of the catchment. problems was located on Poison Creek at the road Top End Waterways Project VICTORIA RIVER CATCHMENT 78 Summary – Victoria River Catchment crossing into Mt Sanford Outstation (Site 9a_4). Exotic species were widespread in the riparian Stock, and to a lesser extent the vehicle crossing vegetation, being recorded at over three-quarters and access track, have caused severe erosion of of sites. A total of nineteen species were recorded, both the bed and banks at this location. including eight that are declared noxious in the Northern Territory. Bars were widespread and were recorded at nearly three-quarters of sites, averaging 18% of the bed The maximum number of different exotic species and ranging to as high as 55%. Bars with recorded at any one site ranged from 0-7. The encroaching vegetation and alternate bars were the mean total cover of exotic species in the riparian two most prevalent bar types. zone was 11%, ranging from 0-42%. One-third of sites recorded the highest category for exotic Nearly half of sites had no factors affecting bed species cover (>16%). These sites were along the stability, however at the remaining sites, the major Victoria, Bullo, Baines and Wickham Rivers, and factor affecting bed stability was grazing, with bank Jasper, Giles or Wattie Creeks. Nearly half the erosion, concentration of flows, instream siltation sites had between 1-15% cover for exotic species and bed deepening contributing to a lesser extent. and the remaining 21% of sites had no exotic species recorded in the riparian areas. ♦ Bed and Bank Sediments The most common exotic structural types were A range of size classes, from clays to boulders, vines and forbs. Passiflora foetida, a naturalised were recorded in the river bed and banks. Pool vine, Parkinsonia aculeata and Xanthium habitats had a higher proportion of smaller bed occidentale were the three major species recorded sediments; runs and riffles had a range of bed throughout the catchment, recorded at 60%, 30% sediment types; and rapids had a higher proportion and 30% of sites respectively. Passiflora foetida of cobbles and boulders. The sediments along the was recorded in all sub-catchments, although lower and upper banks for all habitat types generally had a low percentage cover (1-5%). consisted mainly of smaller sediment sizes (eg Parkinsonia aculeata was recorded in most sub- small sand and clays), except rapid habitats, which catchments with 6-10% cover in all sections of the had boulders on the lower banks. Victoria River, on West Baines River and Gregory and Delamere Creeks. Xanthium occidentale was ♦ Riparian Vegetation also recorded in most sub-catchments, particularly in the lower reaches of Victoria River and West All sites were assessed as having moderate to high Baines Rivers, where percent cover is between 6- cover and structural diversity for riparian vegetation 15%. Other noxious species recorded at a high except one estuary site, which rated as low. The proportion of sites included Caltropis procera and average width of the riparian zone was 23m Hyptis suaveolens. ranging up to 155m. Only one site on Giles or Wattie Creek recorded a narrow riparian width of ♦ Aquatic Vegetation less than five metres. 15% of sites had riparian widths of greater than 40m, including sites on the Two-thirds of sites recorded the presence of larger river systems: Victoria, Bullo, East Baines, aquatic vegetation. Emergent aquatic vegetation Wickham and Armstrong Rivers. was more widespread (59% of sites) than submerged vegetation (21%) and floating A range of structural categories were present in the vegetation (6%). Emergent vegetation was riparian vegetation except for tall trees >30m and recorded in all but two sub-catchments, Armstrong salt marsh. Trees, shrubs, forbs and grasses were and Camfield Rivers. The most common emergent the most prevalent structural types (recorded at vegetation types included Melaleuca leucadendra over 90% of sites). Grasses provided the highest and Pandanus aquaticus. Submerged vegetation percentage cover of all structural types, followed by was recorded in the Victoria, Baines, Camfield, trees and shrubs. Wickham and Humbert Rivers, and Gregory or Delamere and Giles or Wattie Creeks. The most Eucalyptus camaldulensis was the most prevalent submerged vegetation type was Chara widespread native overstorey species, followed by sp. Floating vegetation was only recorded in very Lophostemon grandiflora, Terminalia platyphylla, low densities in Bullo, Baines, Wickham and Pandanus aquaticus, Ficus coronulata and Humbert Rivers and Giles or Wattie Creek. There Melaleuca leucadendra. Acacia holosericea was were no exotic aquatic vegetation