The Cross-Drain Spacing software has been developed by Forest Service scientists and engineers to model potential sediment yield for typical forest road conditions based on tens of thousands of WEPP runs.

One of the most common forest road conditions leading to sedimentation of streams is where a road experiences erosion between cross drains (culverts or open drains), and the runoff from the lower cross drain is routed over the fill slope and across a buffer area toward a stream.

On March 30, 1999, the X-DRAIN datafile was updated from values reported by WEPP version 95.7 to those reported by WEPP version 97.3. In addition, several climate files were improved.

In late 1999, a new the X-DRAIN datafile was again updated using improved climate data and augmented with an additional 50 or so climates. A zero-buffer-length option was added, and the range and selection of input parameter values was changed from the earlier versions (and from the table given below). WEPP version 98.4 was used as the modeling engine.

The cross drain programs are appropriate for use for all insloping, flat-surfaced, rutted, or outsloping roads.

The cross drain programs are not appropriate for those roads that cross streams or drain directly into streams; the current practice is to address live-water crossings as site-specific problems.

In order to exploit the ability of WEPP to predict sedimentation from roads, and to make the results easily available for field application, 52,800 runs of WEPP version 97.3 were made for combinations of

1. buffer slope (4, 10, 25 and 60 percent)
2. buffer length (10, 40, 80 and 200 m)
3. soil type (five representative types)
4. climate (33 spread across the continental United States)
5. road gradient (2, 4, 8 and 16 percent) and
6. cross drain spacing (10, 20, 40, 60 and 100 m)

The calculated quantity of sediment yield delivered at the bottom of the buffer for each scenario was stored into a database.

X-DRAIN is an interface to access this database. The user selects one value for each of the first 4 parameters listed above and specifies a road width, and a twenty-cell table of average annual sediment yield in kilograms per meter of road length (spacing between cross drains) for the specified road width is reported, one value for each road gradient and drain spacing.

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X-DRAIN is no longer available for download as a stand-alone Windows program. We consider that version to be too outdated now. We have no plans to upgrade the Windows version of X-DRAIN.