Delta Irrigation Enhancement Project – Delta, British Columbia

Delta-mapThe Corporation of Delta’s irrigation system relied on gravity water intakes at multiple locations along the approximately 15-kilometre (km) tidally influenced segment of the lower Fraser River. Due to the tidal influence, the availability of suitable water for irrigation depended on tide elevations and the salinity level of the Fraser River water, which gradually decreases over distance from the Pacific Ocean. Water was distributed mostly by gravity, with the support of two irrigation lift stations to approximately 3,000 hectares (ha) of irrigated land, or slightly less than half of the 6,300 ha of cultivated land in Delta. Demand estimates indicated that the irrigated portion of the cultivated land will increase from less than half to more than 75% in the future.

Delta Irrigation Enhancement ProjectThe objective of the Delta Irrigation Enhancement Project (DIEP), an element of the Agricultural Enhancement Strategy of the South Fraser Perimeter Road project, is to increase agricultural productivity through enhanced irrigation water supply capacity that satisfies future demands, improves quality (salinity) of the supplied water, and improves reliability of the water supply.

After estimating future demand and its spatial and temporal distribution, the concept development for the DIEP consisted of three major milestones: the selection of a pumped intake location, definition of the major delivery routes, and identification of the key control structures. Consultation with members of the Delta Farmers Institute (DFI) and Delta was an essential element of the concept development.

Two years of monitoring the Fraser River water salinity at the most upstream gravity intake location (80Street) and a 5-km-long river segment upstream of that proved that 80 Street is the appropriate location for the irrigation water intake. The 32-km-long major delivery routes include 8 km of new irrigation channels and 3 km of closed conduits, and follows existing ditches the rest of the way. Control structures include the 80 Street Pump Station, two irrigation lift stations, three automated control gates, and several minor control structures. The 80 Street Pump Station is reversible, operating as an intake during the irrigation season and as a discharge during the drainage season, contributing to improved flood protection of the area.

The system is designed to an initial 2.1 cubic metres per second (m3/s) continuous and 3.0 m3/s peak flow capacity that could be expanded to 3.0 m3/s continuous and 4.0 m3/s peak flow in the future. The intake pump station is equipped with salinity sensors that will stop pumping when Fraser River water salinity at the intake exceeds a pre-set threshold, prevents salt water entering the system, and resumes pumping as soon as the salinity level falls below the threshold.

Big Slough Control GateThe supply system is demand-controlled and delivers water when irrigation is active anywhere in the system, but delivery is stopped when irrigation is stopped, or when ample water is supplied by summer storm events; thereby, preventing the flooding of low-lying areas. Delivery control is provided by automated downstream or upstream water level control gates, and pump operation is controlled by water surface elevations at remote locations in the system.

The Delta Watershed Model (based on an XPSWMM platform) in irrigation mode setting was used extensively for evaluating system configuration options and developing the functional design of the system.

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