Catchment characteristics

• catchment of a river is the area from which excess water flows towards that river
• catchment characteristics determine hydrological processes and when they change, these processes will change too leading to higher or lower discharges
• 3 most important landscape characteristics: topography, land cover and geology
• outlet: endpoint of river, channel, or stream that drains into a larger body of water
• catchment delineation: determining catchment boundary/water divide
• surface water divide found by following river channels upstream until their sources and drawing the divide between channels leading to outlet and channels leading to different rivers
• topographical water divide: a line of high ground that separates two drainage basins
• topographical water divide can deviate from actual water divide because infiltrating water may hit an impermeable layer in ground and be led in another direction underground
• groundwater divide: the line of separation between groundwater flowing to one catchment and flowing to another
• catchment extent increases in downstream direction
• 3 zones in catchment: upper course, middle course and lower course
• zone 1 (upper): consists of various sub-catchments with dense dendritic network of channels called production zone (main region where surface water and sediments are found)
• zone 2 (middle): has distinguished main channel which often meanders through landscape called transport zone
• zone 3 (lower): delta where river divides into multiple branches as result of flat landscape and large amount of water and sediment called deposition zone
• topography (variation in elevation) has role in formation and transport of surface water
• appearance of current channels is result of erosion and sedimentation
• draining area of certain point in landscape is surface area above it (uphill)

  • if large, large amount of water has to pass increasing wetness
  • if local slope is high, water flows quickly away from point, reducing wetness
• topographic wetness index: ratio between draining area and local slope
• converging hillslope: funnel shape, all water led to one point, bottom has high topographic wetness index
• diverging hillslope: less wet because water is spread out more
• parallel hillslope: neither diverging nor converging
• slope of area can be straight (same slope everywhere), concave hillslope (slopes higher near top) and convex hillslope (slopes higher at bottom)
• presence and type of vegetation impact hydrological processes
• subsurface plays role in storing and transporting water
• porosity: fraction of open spaces between soil particles and determines how much water can be stored in ground
• conductivity: measure of how easy it is for water to flow between soil particles and determines how quickly water is transported
• porosity and conductivity determined by size, shape and origin of soil particles

  • gravel: high conductivity
  • sand: medium conductivity
  • clay: low conductivity
• peat has high porosity but low conductivity because it consists of partly composed plant material which fixates water
• aquifer: layer of permeable soil and can store and transport water well
• soil depth is important factor determining catchment's response to rainfall
• digital elevation model (DEM): gives elevation for each pixel on a map measured with radars on satellites
• catchment characteristics and hydrological processes vary in space leading to different hydrological processes in different parts of catchment and predicting river discharge