WMS:MODRAT Relief Drains

When the reach where a relief drain exits the line is selected, the items under the Relief Drain heading will be active. The first item defines how the hydrograph at that point will be split between the main line and the relief drain. Four options are available:

• Computed percentages – This option requires the user to input the peak flow, in cfs, to remain in the main drain (usually the peak capacity of the drain). The hydrograph is split based on a percentage computed as the ratio of specified flow rate to the hydrograph peak flow rate. The hydrograph remaining in the drain has peak flow entered by the user, with residual flow transferred to the relief drain.
• Specified percentage – This option requires that the user input the percentage of total flow to remain in the main drain. The hydrograph will be split strictly on a percentage basis, with the specified percentage remaining in the drain and the remainder transferred to the relief drain.
• Specified Drain Capacity – This option requires that the user specify the existing drain capacity (cfs). The hydrograph will be separated such that all flow up to the peak flow will remain in the drain, with excess flow transferred the relief drain.
• Specified Relief Capacity – This option requires that the user specify the drain capacity, in cfs. The hydrograph is split such that flow up to the specified capacity goes to the relief drain, with all flow above the drain remaining in the existing drain.

Related Topics

• Editing MODRAT Parameters
• Length
• Slope
• Conveyance Type
• Manning's N
• Reservoirs