Low Tail-End Flow When the Pressure Looks Fine

No - the readings argue against a pump problem. 2.2 bar at the head and 2.1 bar at the far end of the sub-main means the pump is delivering pressure and the main is holding it; only 0.1 bar is lost over the run, so neither the pump curve nor main friction explains a 50% fall in emitter flow.

What the readings rule in: a restriction downstream of the gauge - clogged emitters and laterals, biofilm and silt, and possibly a blocked or kinked lateral. If the sub-main had failed, the far-end gauge would read much lower. If the pump were worn, the head gauge would sag under load.

Measure before spending:

1. Emitter discharge by the catch-can method at head, middle and tail of three laterals - establish the actual distribution.
2. Filter ΔP clean versus dirty, and open the filter to inspect the screen for algae and silt.
3. Open the ends of two laterals and observe flow and colour - no flow at all points to a blockage or a closed/blocked end, not low pressure.
4. Operating pressure at the pump while running, to compare with the pump curve.
5. Soil moisture at the tail rows to confirm the crop is genuinely under-watered.

The wet patch over the track is a separate finding: the sub-main is leaking there.

Priority order:

1. Stop the leak at the track. Isolate the section, excavate, confirm the break (a wet patch over a buried line under traffic is almost always a cracked joint or a point load failure), and repair with a compression repair coupling or a short replacement spool. Backfill with sand bedding and a concrete slab so it does not recur. Do this first - it wastes water and undermines the track.
2. Fix the dry laterals. Open each end, flush; if nothing moves, disconnect at the sub-main and rod or replace. Confirm whether the end cap is blocked rather than the lateral being dead.
3. Rehabilitate by treatment. Chlorinate to kill algae and biofilm (shock dose per label/extension guidance), hold, then flush every lateral until clear. Acidify separately if carbonate scale is present - never mix acid and chlorine.
4. Flush properly and often. Flush velocity of 0.3–0.5 m/s at the lateral end; flush the sub-main first, then laterals, so debris is not pushed back into emitters.
5. Re-measure discharge at the same three points and record it.

Also address the dry runs: the pump has cavitated twice; check suction conditions, foot valve and the low-level cut-out before the next season.

Daily / every irrigation

• Read and log filter inlet and outlet pressure - a rising ΔP above about 0.5 bar means clean now, not next week.
• Backwash the screen at the end of each irrigation day while canal water is running; algae multiply overnight in a wet screen.
• Check the pump for noise, vibration and priming; two dry runs already suggest a suction or cut-out fault.

Weekly

• Open and flush lateral ends, working from the farthest block back to the head.
• Walk the block and look for wet patches, leaks, broken risers and blocked emitters.

Monthly

• Clean the filter element by hand, inspect for tears, and check the pressure gauge against a second gauge.
• Measure emitter discharge at three points and log it - this is how a 10% decline is caught before it becomes 50%.

Seasonal

• Chlorination and, if needed, acidification; pump servicing; check valves and air release.

Records: a single sheet per irrigation with date, set, hours, filter ΔP, flush done (Y/N), any repair, and the discharge check. Without it, every diagnosis starts from zero and the farmer's memory becomes the only evidence.