The Petite-Rhue Spillway

Similar project

The Petite-Rhue Spillway

The Midi Hydroelectric Company asked ISL to produce a digital 3D hydraulic modeling of the spillway.

Projet : 

The Midi Hydroelectric Company has to carry-out a recalibration of the Petite-Rhue spillway. Actually, its current evacuation capacity is insufficient for safely channeling the flood flow for the dam (millennium flood).The recalibration project was defined following a hydraulic modeling on a physical model. However, the initial project led to reinforcement works on the lock wall on the right bank of the spillway which were more significant than expected, given the estimated heights of the water of the project flood.

The initial project, defined following a hydraulic modeling on a physical model consists of:

  • Modification of the flow approach zone on the spillway
  • Lengthening the spillway
  • Enlarging the chute
  • Modification of the slope of the chute


ISL’s aim is to study the variants for developing the mounting, with the help of a 3D digital hydraulic modeling using ANSYS CFX, in order to reduce the waterline in the chute. The objective being to avoid strengthening works on the lock wall on the right bank of the spillway.


Two spillway chute developments will be tested:

  • Removing rocks from the lock wall on the left bank
  • Removing rocks from the bottom of the chute ( deepening the chute)
Mission : 

ISL Engineering is responsible for studying the various options for developing the chute, using 3D digital hydraulic modeling. The different steps of the study are presented below:

Construction of a three-dimensional digital model

  • Construction of a digital model of the land using MapInfo to create a model of the reservoir, the chute and the downstream restitution of the construction
  • Construction of the spillway’s geometry directly under ANSYS CFX


Boundary Conditions

  • Introduction of a rating or a flow on the upstream limit of the model
  • Introduction of a downstream level on the flow of water on the downstream limit for the given flood


Calibration of the model on the initial project of recalibrating the spillway

  • Refining of the tetrahedral meshing
  • Modification of the natural terrain and concrete surfaces
  • For the rating of a given reservoir, the flow evacuated by the reservoir calculated by the 3D hydraulic modeling is bigger than that determined with the physical model. Nevertheless, the calibration of the model is satisfactory for the flows near the project flood because there is only a slight difference (less than 4%)
  • Given the uncertainties with calibration, the flow of the project has been increased for dimensioning the reservoir


Study of proposed developments

  • Case No.1: Removing rocks from the lock wall on the left bank of the chute
  • Case No 2: Deepening the chute
Le projet
Pays/région : 
Société Hydro Electrique du Midi (SHEM), groupe GDF Suez
Période :