The Low Flow Pipe dialog window defines the characteristics of any pipe under the channel section. If a pipe slope is provided greater than 0.0% with no diameter, XPRafts will use Manning's Equation to estimate a pipe diameter large enough to just contain the total inflow hydrograph at the top of the link after basin routing, if present.

Natural surface information may be entered for any reach in the system. The offset "x" (m, ft) and the elevation (m, ft) is entered into the table shown. These values are additional to the cover level entered for each pit, which is assumed to be a design level. Any number of values may be entered between each pit. The Natural Surface profile is used when checking cover requirements following a Design run or prior to an Analysis run. Any conflicts are reported to the error log and may be viewed as usual. Note that if both a Design Surface and Natural Surface are defined, then the Design Surface takes precedence in the checking that is performed.