Runoff GenerationBrian FinlaysonSchool of Anthropology, Geography and Environmental StudiesThe University of Melbourne

PremisesThere is significant locational specificity in runoff generation and delivery.Much of what we know comes from small (usually experimental) catchments in steep and humid environmentsThe bulk of the agricultural and grazing lands in Australias major river basins are characterised by flat topography and sub-humid to semi-arid climates

The major issue in relation to runoff generation in these catchments concerns the generation and transmission of surface runoff There are two components to this:How and where surface runoff is generated How and where that runoff makes its way into and through the drainage network

Krui River Headwaters

Merriwa River

Mooki River

Comet River

Characteristics of the Comet River at Comet Weir (130501A/130504A)

(1919/20 to 1999/00)

Mean annual areal rainfall 660 mm

Mean annual runoff (MAR)455,000 ML (27.6 mm)

Catchment area16,400 km2

Coefficient of variation of annual flows (Cv)1.6

Flash flood index (Iv)1.15

Base flow index (BFI)0.17

Runoff ratio (coefficient) 4.2%

Comet River

Figure 3: Example of baseflow separation for the 1920 water year using the Lyne and Hollick filter (Nathan and McMahon, 1990)

Comet River

Comet RiverChannel connectivity

Comet River

Summary of catchment characteristics

Catchment Area Av Slope ()% Well Connected

Brown River 1222 5.99.4

Corella Ck 144 1.71.0

Moolayember Ck 61715.321.6

Comet River

SummaryWhere and how is surface runoff generated?Soil properties (surface sealing, depth, permeability etc)Topography (slope, contour concavity, water surfaces, bedrock outcrops)Land use (grazing, cultivation, irrigation)

SummaryWhere and how does it join the channel network?Slope-channel couplingNon-channel topographic networks

SummaryHow does the channel network deliver water and entrained sediment through the catchment?Channel network continuityInternal storage basins

Most of the runoff is surface runoff or quickflow of some kindUpstream ends of the experimental catchments for this project - note typical - in the textbook sense - topography and drainage network.Note disconnected drainage system even in this areaOver the divide to the north - Mooki River. How much of the runoff in the channels in the SE of this map area ever leaves the catchment?Baseflow index (BFI) = baseflow/total flowComet - for all data = 0.17 (wettest year 0.26)Victoria (Laceys data) mean is 0.55World survey - most >0.50

1920 water year runoff 14mm (mean is 27mm)1949 runoff is 117 mm (mean is 27).Action button

1. Map of well connected slopes2. Topo map showing arrow ending on rivers3. Photo of channel end after floodPotential uses of laser scanning of topography