sheeting-estimate.md

Polyethelene sheeting estimation for sandbag wall

This expression returns the amount of polyethelene sheeting needed to fill sandbags to construct a sandbag wall of a given length, height.

Use cases

This example can be used in flood response and control activities to ensure necessary resources are deployed. Calculations are derived from this site.

Workflow

Copy and paste the expression found in the expression template below to the Arcade editor in ArcGIS Online, the relevant location in ArcGIS Pro, or the relevant location in a custom app.

To configure the script to your layer, edit the first line to use the fields representing the desired wall height.

var finishedHeight = $feature.FinishedHeight;

Expression Template

This Arcade expression will return the square feet of polyethelene sheeting required to construct a sandbag wall.

// Replace with appropriate field for height 
var finishedHeight = $feature.FinishedHeight;
var finishedWidth = 3;

// assume length of dike base and top are equal
// e.g. straight line for dike wall
var embankmentCrestLength = Length($feature,"feet");
var embankmentToeLength = Length($feature,"feet");

function CalculatePolySheeting(wallLengthAtCrest,
    wallLengthAtBase,dikeHeight){

    // dike wall width is assumed to be 3x height
    var dikeWidth = dikeHeight * 3;        

    // calculate the slope of the embankment that needs 
    // to be covered (water side)
    var slopeLength = Sqrt(pow(dikeHeight,2) + 
        pow((dikeWidth / 2),2));

    // Assume dike wall top (crest) is one sandbag wide, ~1'
    var embankmentCrestWidth = 1;

    // calculate area to be covered on the side of the embankment
    var embankmentArea = (wallLengthAtCrest + 
        wallLengthAtBase) / 2 * slopeLength;

    // determine area of the crest of wall to be covered. 
    // Assume one sandbag in width (~1')
    var crestArea = wallLengthAtCrest * embankmentCrestWidth;

    //compute total area
    return Ceil(embankmentArea + crestArea,0);

}

If(wallType == 1)
    return CalculatePolySheeting(embankmentCrestLength,
        embankmentToeLength,finishedHeight);
Else
    return "-";

Example output

See this web map for examples of how to use this expression in ArcGIS Online.