Smoothing Distance (m/% or ft/%)
Defines how rapidly the slopes can change. This effectively smooths the surface so the grade changes do not change too rapidly e.g. from minimum slope to maximum slope in a short distance. A typical value is 100 m/% (300ft/%) but depends on how much soil you want to shift versus how smooth you want the finished design. The grade changes are calculated at every grid point.
For example, if the calculation grid spacing is set to 10m, and Smoothing Distance is set to 100 m/%, then at each grid point the slope can change a maximum of 0.1% (10/100). Eg from 0.1% to 0.2% at one grid point, then the next grid point it could go from 0.2% to 0.3%, etc Note: You need to tick the tick box ‘ON’ to adjust the value and use this constraint in the calculations.
Example
Existing Topography
Proposed Topography V01
Calculation Grid Spacing: 10m
Smoothing Distance: Ticked OFF (No smoothing)
Proposed Topography V02
Calculation Grid Spacing: 10m
Smoothing Distance: 50 m/% (Main Slope and Cross Slope)
Ridge Subzone added
Smoothing Distance should always be included in any design. Otherwise, you will get a rough result and the field will not drain well and OptiSurface will get blamed when it is actually a poor designer.
Any design under 100m3/ha should have smoothing increased to get earthworks up to at least 100m3/ha. Any designs with earthworks above 100m3/ha before smoothing should have smoothing increased until earthworks increased at least 20% and maybe more.
We typically increase smoothing gradually and earthworks will increase gradually then when we push smoothing too far, earthworks jumps up rapidly. So then we back off the smoothing a little and go with that.