Paddy Irrigation Tools

Step 1 — High points finds the high (and low) ground of every paddy block from a DEM. Step 2 — Gravity command then asks whether every block can be irrigated by gravity: Field → TC → SC → MC → Reservoir.

After a run in step 1, Next: Step 2 opens step 2 with the same block layer and the new HighestPoints layer filled in. Step 2 also works on its own with any block layer and any point layer — one point per block, with an elevation field.

Step 1 — High points

For every feature of the ticked block layers (polygons or lines) the tool finds the highest cell of a DEM and adds one point layer, HighestPoints, with src_layer, block_fid, the block attributes you tick, elev, X, Y, Lon, Lat and Top_cells — plus dist_along for lines. Tick Lowest point as well to get a blue LowestPoints layer.

• Polygons count the cells whose centre is inside the polygon, like QGIS zonal statistics. Lines count every cell the line passes through, and the point is placed on the line.
• Combine features with the same value of gives one point per group — per BM name, say — instead of one per feature.
• Top_cells above 1 means a flat top: several cells share the highest value.

Method (polygon blocks)

For gravity irrigation design the raw highest cell is often a tree crown, hut or dike. The High / low point method list chooses what "highest" means:

• Top of general slope (default) — the DEM inside each block is ground-filtered (a morphological opening removes trees, dikes and huts narrower than the Ground filter window), then smoothed, so the point marks the high side of the field rather than a spike. elev is the ground elevation there, so the water level needed is never under-estimated; Smooth_z and Raw_cell are kept for comparison.
• Highest ground — ground filter only.
• Highest DEM cell — the raw cell, trees and dikes included. Lines always use this.

The two terrain methods also give each block a robust plane fit of its ground: Slope_pct, Fall_m, Aspect / Flow_dir and Fit_R2. A block with a fall under 5 cm is almost level and its high/low point is weakly defined — the log says so.

Step 2 — Gravity command

1. Field level each block needs: FSL_req = top of block + field water depth.
2. Plot-to-plot supply: neighbouring blocks (dikes and gaps up to the tolerance are bridged). Block A can feed block B when top_A − top_B is at least the spill loss. Head blocks have no neighbour high enough and need a canal turnout.
3. Turnouts: the nearest point on a canal within the search distance. The canal water level needed there is FSL_req + turnout loss + field-channel gradient × field-channel length.
4. Service: blocks are processed from high to low, each served directly from a canal or plot-to-plot from a served higher neighbour.
5. Canal levels. DESIGN needs no water levels: it gives the level each canal needs at its upstream end (TC → SC → MC) and the reservoir level needed, naming the block that controls each canal. CHECK compares your canal water levels with the need at every turnout, junction and the reservoir.
6. With a DEM, the ground along each canal shows how far the design level is above (fill) or below (cut) the ground.

1. Open KGA Irrigation Tools > Paddy Irrigation Tools.
2. On Step 1, pick the DEM and tick the block layers.
3. Choose the high/low point method — leave it on Top of general slope unless you want the raw cell — and set the ground filter to the width of the widest tree crown or dike.
4. Tick a save format if you want the results kept; the layers are temporary otherwise.
5. Run it, then press Next: Step 2 to carry the blocks and high points across.
6. On Step 2, add the canals and reservoir, choose DESIGN or CHECK, and read the report.

• Block layers in edit mode cannot be written to: save and stop editing, or tick Create new output layers.
• Run time grows with the number of blocks and the DEM resolution; use a coarser analysis resolution for a first pass.
• Block cleaning needs a DEM in metres and is skipped for a DEM in degrees.
• The result layers are temporary until you tick a save format.
• In step 2 you may move high points by hand — tick Re-sample elevation from the DEM so moved points get a fresh ground elevation.