Territory Stories

Effect of vegetative cover on USDA curve numbers for pastoral catchments in the Australian semi-arid tropics



Effect of vegetative cover on USDA curve numbers for pastoral catchments in the Australian semi-arid tropics

Other title

J.A. Motha and M. Dilshad.


Motha, J. A.; Dilshad, M.


E-Publications; E-Books; PublicationNT; DLPE technical memorandum ; no. 97/01




Made available via the Publications (Legal Deposit) Act 2004 (NT).


Date:1997; Bibliography: p. 13-14.




Pastures -- Northern Territory; Soil erosion -- Northern Territory

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Land Resource Conservation Branch, Land Resources Division, Department of Lands, Planning and Environment

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DLPE technical memorandum ; no. 97/01


14 p. ; 30 cm.

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Check within Publication or with content Publisher.

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Effect of vegetative cover on USDA curve numbers In Figure 1, the optimised CN2 values for improved as well as native pastures have been combined; hence the scatter. Note that CN2 for SCI serves as the pivotal point at near-zero cover, thereby dissociating itself from the influence of pasture type. The derived function possessed a value of 85 at zero cover, and decreased 0.49 units for every 1 % increase in cover. Although CN2bare was felt to be lower than was expected (based on the study ofDilshad and Peel, 1994) cover had a pronounced effect on CN2. Based on a general understanding of runoff on Australian soils, it was deduced that CN2 stays constant beyond 80% cover. Due to the difference in vegetation as well as difference in the cultural history of the plot, the CN2 for SC5 should be treated separately. Figure 2 gives the cover-CN2 function for improved pasture plots, all three of which have a history of previous cultivation. CN2 was 91 when bare and decreased 0.52 units for a cover increase of 1%. These values look reasonable based on the study ofDilshad and Peel (1994). 100 80 "- " -"+---" - " - " -~'---" -'-+" - " - " -'-1"-'-" - " -+--_ ... _ .. !-..... _ ... +_ ........ . ! ! i i ! ! i 60 . : -+----,r-+- N ",.,' I I ~ 40 __ ._._.J Y = -~.52x ; 91 .03!--_-t---EJ9f---_-t___t-___ 20 r2 = 0.59 ... _ .. _._.l .. _ .. _ .. _.~ __ ._ .. _ .. _l_ .. _._._ .. l .. _ .. _._ .. 1 .......... _ f . . ! i O+-~---+---r--+---r--+---r--~--r-~ o 10 20 30 40 50 60 70 80 90 100 Cover ('Vo) Figure 2. Cover-CN2 Function for Improved Pasture Catchments at DDRF In Figure 2, there is an obvious outlier; the optimised CN2 of 42 for SC4 was derived from limited opserved runoff data. Although it is not desirable to obtain the cover-CN2 function from three data points, it is interesting to check the effect of omitting the CN2 value for SC4. 6

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