Erosion Wattles & Fibre Rolls on a Slope: Rows, Units, Stakes & Total Length

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 6 inputs are read from the form on every keystroke: Slope Length, Top to Toe, Slope Width across the Contour, Row Spacing down the Slope, Length of One Wattle, Overlap Where Wattles Meet and Stake Spacing along a Wattle.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Wattles to Order together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Rows down the Slope, Wattles per Row, Total Wattle Length, Stakes, Slope Area and Wattle per 100 m² of Slope — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

The slope is 50 m wide, but a row of 3 m wattles with 30 cm laps takes 57 m of wattle.

How to use it

1. Work through the input groups in order — Slope and Wattle & Stakes. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Wattles to Order in the dark results panel — that is the headline figure, expressed in units.
4. Check the supporting rows underneath (Rows down the Slope, Wattles per Row, Total Wattle Length, Stakes, Slope Area and Wattle per 100 m² of Slope) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Wattles to Order before a trial is booked, so machine time and material in Geosynthetics & Civil Engineering are committed against a calculated figure rather than an estimate.
• Costing and quotation — Wattles to Order is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Slope Length, Top to Toe) shows how much of the gap in Wattles to Order each variable explains.
• Teaching and study — the accepted ranges bracket normal Geosynthetics & Civil Engineering practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• Row spacing, the overlap and the stake spacing are the plan's; erosion manuals set spacing by slope steepness and soil, and the tool has no figure of its own. Rows run across the full slope width on the contour, the first one row spacing below the top; a row at the toe is counted when the slope length is a whole number of spacings. Each wattle is staked along its length at the spacing given with one stake at each end; some plans stake through the overlap instead, which saves one stake a join. Trenching the wattle in is not counted. **This is a quantity take-off; where wattles belong on a slope is the plan's decision.**
• Every input is bounded to the range normal practice occupies (Slope Length, Top to Toe 1 to 1000 m, Slope Width across the Contour 1 to 10000 m and Row Spacing down the Slope 0.5 to 50 m, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Standards and further reading

• The local erosion and sediment control manual, which sets row spacing by slope and the trenching and staking detail.
• The product data sheet: fill (straw, coir, wood fibre), netting, diameter and length.

Questions people ask