River Hydraulic Rating Analysis: Using LiDAR and HEC-RAS in the Kimberley Region, Western Australia

Michael Harris and Leith Bowyer - WA Dept of Water , 22 October, 2010

The use of river hydraulic analysis is well established in engineering hydrology for use in flood studies, and more recently in determining environmental flows. Analysis of river hydraulics is also important in understanding how to reliably estimate and measure river flows at gauging stations. Historically, river flows have been measured in a number of ways, most commonly with current meters and more recently quantified using hydraulic models. These models fundamentally depend on defining river channel geometry, river slope and channel roughness.

Flow analysis at gauging stations using hydraulic models has not been widely used. Recently, a number of river reaches in the Kimberley were surveyed and the flow modelled to substantiate existing and to develop river flow rating curves. Reliable rating analysis for gauges in the Kimberley has historically been limited by technical, operational and funding / resourcing issues.

The river hydraulic rating analysis focused on defining or verifying the rating curve for mid to higher flows measured by the gauge. The gauges used in the hydraulic rating analysis ranged from river reaches with a simple channel geometry and channel roughness including a main channel with a uniform bed material and regular banks and overbank flow, to very complex channel geometry and channel roughness including a main channel with extra channels or distributaries on the floodplain.

The focus of this paper is to discuss the applicability of Aerial Laser Survey (LiDAR) and RTK surveying technology, in the development of stage/discharge rating curves at gauging stations. The following approach was trialled at 9 gauges across three general geomorphic features commonly found in the Kimberley. These were:

  • simple channel and overbank situation,
  • gorge complex and
  • main channel with distributary floodplain system