Real-time irrigation forecast system - Rangitata diversion race, Canterbury, New Zealand

DHI were engaged by Barrhill Chertsey Irrigation Limited (BCI) to build a real-time flow forecasting and optimisation system for the Rangitata Diversion Race (RDR). The inclusion of the BCI irrigation scheme into the RDR diversion race and associated, complex, water swapping required that a “smart” real-time forecasting and optimization system be designed, developed and implemented.

The RDR diverts water to 64,000 hectares of Canterbury agricultural pasture, making it New Zealand’s largest irrigation system. The construction of the race began in 1937 and was completed in 1941. The canal is 67 kilometres long, 10 metres wide and 3 metres deep. Structures along the canal include siphons, check gates, radial gates and spillways. The RDR delivers water to four irrigation schemes: Mayfield Hinds; Valetta; Ashburton Lyndhurst; and Barrhill Chertsey (a recent addition). The RDR also delivers water to a number of stockwater off-takes.

Since the 1940’s when the scheme was commissioned it has been able to be successfully managed by the application of water restriction rules by the duty operator, until recent expansion of the system. In 1998 groups combined to form BCI. In 2001 consent was granted to BCI to extract 17m3 /s from the Rakaia River to irrigate 40,000 hectares, bringing the total irrigated area to over 100,000 hectares. The BCI Scheme has a long term contract with TrustPower Limited to take water from the Rakaia River and pump it to the district’s existing irrigation canal, the RDR. The BCI scheme includes small scale storage/buffer ponds, off-takes and control structures that allow complex water delivery to be undertaken.

Key system components:

• Calibrated hydraulic model representing the existing RDR canal (pre BCI)
• Hydraulic model representing future RDR canal (including BCI) which optimises on storage and spills back to the rivers
• Web based Dashboard Interface (DI) to allow for system inputs, displays of forecasts and capture of data
• Real-Time Software Shell that links the input data, real-time field data and the models together

Currently the irrigation demands and river restrictions are operated at a daily resolution. The DI allows all four irrigation schemes to submit a water order and the RDR operator to submit river inflows. Also the DI allows the input of BCI time varying storage pond water levels and RDR flow control structure settings that are not controlled by telemetry (manually controlled), such as maintenance gate openings.

The DHI system carries out full hydrodynamic calculations (in 1D) and produces future set points to deliver an optimised water allocation by balancing supply to demand priorities across the whole scheme. Model simulation times are less than 1 hour with the model running 24/7.

The system can also be used in parallel mode to allow for use in emergency situations that could develop during operation. The software platform used for the system is the MIKE by DHI software (MIKE 11 – channel flow and control structure operation; MIKE AUTOCAL – system optimization; Dashboard Manager – to develop and publish the Dashboard Interface; MIKE FF – forecasting).

Currently the DI is in final stages of testing and the model is undergoing real-time testing. It is expected that this project will be completed over the next few months. Likely future expansions to this project are additional large scale storages and inflow forecasting.