The following types of unit sanitary loads are supported in Bentley StormCAD :

Population-based

The most common way of specifying sanitary loads to a sewer system is to make them proportional to the contributing population. Population-based unit sanitary loads define loads as a function of adjusted contributing population. You can select the population loading units that will be used and the unit load per population unit. For example, the unit sanitary load, Home (Average), specifies Resident as the population loading unit, and 280 l/d per Resident as the unit load per population unit.

Non-population-based

Non-population-based unit sanitary loads can be area-based (function of contributing area), discharge-based (function of direct discharge), or count-based (function of a user-defined count).

Area-based

Area-based unit sanitary loads are commonly used to specify industrial loads and steady inflows. Use these unit sanitary loads whenever your load is specified as a function of contributing area. For example, you may use "area residential" (in hectare) as a property of each node and 400 L/day/hectare as the unit loading.

Discharge-based

Discharge-based unit sanitary loads are used to directly specify loads without specifying them on the basis of some other count, such as population or area.

There are two general ways to use discharge based loads:

• Specify 1.0 discharge unit (e.g. l/day, gpd, cfs, etc.) as the unit load. Then, when using the load, specify the total desired load for the loading unit count. For example, you can create a load called Liter per Day whose loading unit type is Discharge, loading unit is l/day, and unit load is 1.0. When you use this load at a manhole, a wet well, or a pressure junction, you specify 50.0 as the loading unit count. This yields a base load of 50 l/day.
• Specify total desired load as the unit load. Then, when using the load, only specify 1.0 as the loading unit count. For example, you can create a load called Industry XYZ whose loading unit type is Discharge, loading unit is l/day, and unit load is 2000.0. When you use this load at the manhole, wet well, or pressure junction, you would specify 1.0 as the loading unit count. This yields a base load of 2000 l/day.

In other words, you can specify a unit load of 1.0 in the Unit Sanitary Load Library and determine the total load at each node through the loading unit count, or you can specify the total load in the Unit Sanitary Load Library and then have a loading unit count of 1.0.

Count-based

Count-based unit sanitary loads should be used for any load that is not area, population, nor discharge-based. These loads allow you to specify any loading unit such as loading per vehicle, machine, or anything else.

Loading units in user-defined counts are treated only as labels. Conversion between these units is always 1 to 1.