Work Item
ASTM WK82815

New Practice for Practice for Determining Annual Rainfall Weighting Factors for Use in Sizing Stormwater Control Measures

1. Scope

This standard will address various methods of determining weight factors, based on site hydrology, that will allow for calculation of net annual removal by a Stormwater Control Measure (SCM), when combined with removal versus flow rate data for the SCM.


weight factors; net annual removal; Stormwater control measures; rainfall intensity


The recently developed standards for measuring performance of SCMs generates data for removal versus flow rate. In order to determine the performance of the SCM in real installations it is necessary to estimate the number and size of flows the SCM will be subjected to. This data can be extracted from the hydrograph for the site. The easiest method for calculating SCM performance is to determine a weighted average of the flow rates * removal at that flow rate. This standard will describe a way to generate appropriate weight factors. The New Jersey Corporation for Advance Technology (NJCAT) has developed a set of weights for NJ but the method is not clearly described in one place. Thus there is no method for consistently developing weight factors for other regions. Inconsistent weight factors can lead to inconsistent sizing and uncertainty as to whether or not the SCM will work as planned. This will be beneficial to manufacturers, regulators and end users in determining if an SCM will meet the desired/required performance over the course of an average year.

The title and scope are in draft form and are under development within this ASTM Committee.


Developed by Subcommittee: E64.01

Committee: E64

Staff Manager: Frank McConnell

Work Item Status

Date Initiated: 07-18-2022

Technical Contact: Graham Bryant

Item: 000