MBB Nelspruit was appointed by ANB/Halls JV in June 2018 for the design of a drip irrigation system for a 150-hectare soft citrus development in Nelspruit. MBB was later also appointed as contractor for the modification work to the existing river pump station and the construction of a new fertigation building, which included all civil, mechanical, electrical and automation works.  The installation of the in-field irrigation was done by ANB/Halls JV.

The project faced numerous challenges in the form of time constraints and technical difficulties as we had to conduct our work on the existing infrastructure of the Halls farming group. The best course of action, it was decided, would be to use the existing river pump station and modify it, accordingly, upgrading it into a state-of-the-art irrigation hub from where the whole irrigation operation could be run.

This was no simple task, though. The first trees were to be planted at the beginning of October while the pump station had to remain in use for the duration of construction since it also supplied bulk water to the Matsafeni Trust’s avocado orchards. Although we were faced with numerous challenges and difficulties, the MBB team was assured of an interesting project that would test our abilities.

None of this stood in the way of us helping the greater society throughout the project. Only local community members were contracted for the pump station civil works, which made the upgrading of the pump station a local project.

The 3-storey pump station consists, amongst others, of two 75 kW pump sets with VSD switchgear, abstracting water directly from the Crocodile River. The total irrigation system capacity is roughly 350 m³/h.  Primary filtration is done at the pump station by three 4-bank automatic backflush disc filters. As per the client’s demand, and to simplify automation, all the block hydraulic pressure control valves are located at the pump station.  This meant a PVC/HDPE mainline had to be installed from the pump station to each irrigation block – all varying in size, from 3 – 5 hectares.  To reduce the number of mainlines, two irrigation blocks were grouped together per mainline.

Every two blocks share

an in-field cluster valve, with a shut-off valve for each block.  Each block has its own sub-mainline with a flush valve. One dripper line is installed for each tree row with 0.7 ℓ/h drippers, spaced at 1m intervals.  The opening and closing of all block control valves are controlled by an irrigation controller.  A GSM commander system allows the starting and stopping of pump sets from a mobile phone.  Each group of two blocks also has a flow meter at the pump station to measure the blocks’ flow rate.

The fertigation system consists of fertilizer storage tanks, mixing tanks, mixing pumps, agitating pumps, air blowers, PVC pipework and a fertigation dosing unit. The fertigation building, constructed adjacent to the pump station, houses six 10 000 ℓ fertilizer storage tanks and three 2 500 ℓ mixing tanks.  Each 2 500 ℓ mixing tank serves two 10 000 ℓ fertilizer storage tanks. Thus, the system makes provision for the dosing of three types of fertilizers at any given time.  Fertilizer bags are manually emptied into the mixing tanks, after which the contents are mixed with the mixing pumps and air blowers. Thereafter, the mixture is pumped to the storage tanks.  Once in the storage tanks, the fertigation dosing unit pumps fertilizer from the storage tanks into the irrigation system in a pre-set volumetric ratio. The agitating pumps and air blowers agitate the fertilizer in the storage tanks at regular intervals to ensure the fertilizer stays in suspension.

After months of hard work and dedication, not to mention overcoming countless challenges, the MBB Nelspruit team, including a number of subcontractors, completed a project to be proud of, and we are confident ANB/Halls JV will benefit from our work for many years to come.

This article is a general information sheet and should not be used or relied upon as professional advice. No liability can be accepted for any errors or omissions nor for any loss or damage arising from reliance upon any information herein. Always contact your professional adviser for specific and detailed advice. Errors and omissions excepted (E&OE)