LANDSCAPE ECOLOGY SREM 3011 LECTURE 13 Dr Brendan Mackey Department of Geography The Australian National University
LANDSCAPE ECOLOGY SREM 3011 LECTURE 13 Dr Brendan Mackey Department of Geography The Australian National University
Main limitation of ' bucket MI method is that it does not factor in catchment hydrological processes: PRECIPITATION EVAPORATION overland flow: infiltration throughflow processes are topographIc Surface own ally driven glacier- INFILTRATION spatial modelling of these processes requires a suit- ably scaled digital elevation model (DEM) GROUNDWATER BASEFLOW Water shed hydrology: the passage of precipitated water through vegetation cover, soil and rock to the stream. Precipitation falls over the whole watershed and is concentrated in stream channels NB Focus here on humid, erosional landscapes, not dry depositional landscapes
Water shed hydrology: the passage of precipitated water through vegetation cover, soil and rock to the stream. Precipitation falls over the whole watershed and is concentrated in stream channels. • Main limitation of ‘bucket’ MI method is that it does not factor in catchment hydrological processes: overland flow; infiltration; throughflow processes are topographically driven spatial modelling of these processes requires a suitably scaled digital elevation model (DEM) NB Focus here on humid, erosional landscapes, not dry depositional landscapes
Simulation models of catchment hydrology: many deterministic and empirical models all model water flow in the catchment as a function of: 1. Topographic characteristics and 2 Soil characteristics Highly parametrised models(eg. CSIRO 'Topog difficult to 'runor implement across landscapes due to lack of required spatial data Therefore' simple'models are“ popular
• Simulation models of catchment hydrology: - many deterministic and empirical models - all model water flow in the catchment as a function of: 1. Topographic characteristics and 2. Soil characteristics - Highly parametrised models (eg. CSIRO ‘Topog’) difficult to ‘run’ or implement across landscapes due to lack of required spatial data - Therefore ‘simple’ models are “popular
Exam ples of profiles across terrain divided into morphological types of landform element C F UX R C UA M LN Position in topo-sequence"as an index of run-on/run-off
“Position in topo-sequence” as an index of run-on/run-off Examples of profiles across terrain divided into morphological types of landform element
Slope lines overlaid on a contour map show ridge lines and course lines SUMMIT N氏S PASS
Slope lines overlaid on a contour map show ridge lines and course lines
Position-in-a-topographic-sequence"an index of whether you are shedding or receiving water But terrain is 3D, therefore position-in- catchment is a better description Area above point in catchment is critical ie the up-slope area or up-slope contributing area At drainage line, USCA is large At crest, USCA is small or o USCA therefore potential discharge( )of water through that point/location
• “Position-in-a-topographic-sequence” an index of whether you are shedding or receiving water But terrain is 3D, therefore position-in-catchment is a better description Area above point in catchment is critical ie. the up-slope area or up-slope contributing area At drainage line, USCA is large At crest, USCA is small or > USCA therefore > potential discharge () of water through that point/location
An idealized catchment above a 20m x 10m plot AE USCA w= plot width A= A/= Specific catchment area Index of unit area discharge Average catchment length (ACL)
An idealized catchment above a 20m x 10m plot: As = A/W = Specific catchment area = Index of unit area discharge = Average catchment length (ACL) A A = USCA w = plot width w
tanB= slope angle bla b Slope for 'landscape unit of analysis'eg plot Index of hydraulic gradient Soil attributes affecting T(transmissivity) a. Soil depth and texture b Soil porosity C Hydraulic conductivity
• tan = slope angle = b/a • Slope for ‘landscape unit of analysis’ eg. plot • Index of hydraulic gradient • Soil attributes affecting T (transmissivity) - a. Soil depth and texture - b. Soil porosity - c. Hydraulic conductivity b a
"Wetness indexis defined as WI=(As * T)/tan R where As is specific catchment area T is transmissivity tanβ is slope angle Based on a great deal of theory! Certain assumptions: a Infiltration constant across landscape b Impermeable layer at fixed depth therefore problems in karst country depositional landscape works better in erosional landscapes
• ‘Wetness index’ is defined as WI = (As * T) / tan where As is specific catchment area T is transmissivity tan is slope angle Based on a great deal of theory! Certain assumptions: a. Infiltration constant across landscape b. Impermeable layer at fixed depth - therefore problems in karst country & depositional landscape - works better in erosional landscapes
Spatial application of wetness index? 一→ Soil attribute data generally unavailable Therefore, assume t is uniform and equal to 1 Topographic wetness defined as an index TWI= As/ tan B ) Interpretation? Therefore factor out soil and therefore need only calculate two topographic characteristics: (1)Asf(USCA, plot width) (2) Slope angle(tanβ)
• Spatial application of wetness index? Soil attribute data generally unavailable Therefore, assume T is uniform and equal to 1 Topographic wetness defined as an index: TWI = As / tan } Interpretation? Therefore factor out soil and therefore need only calculate two topographic characteristics:- (1) As f (USCA, plot width) (2) Slope angle (tan )
