Publication Summary

The purpose of this guide is to provide permittees with detailed descriptions of a few of the easiest or most common methods for taking flow measurements, if they choose to manually collect the data on their own. The intent is to assist permittees in understanding how to meet the permit requirements in a manner that is simple yet also accurate enough to meet Ecology′s needs. Other methods, not described in this guide, such as hydrologic models, in-pipe flow meters, calculations based on pump usage, automated flow devices, and others could also be used. Any flow estimating method that meets the intent of the permit would be accepted by Ecology.

In January 2005, The Washington State Department of Ecology (Ecology) reissued the Sand and Gravel General Permit for process water, stormwater, and mine dewatering water discharges associated with sand and gravel operations, rock quarries and similar mining facilities. A new condition has been included in the permit that calls for the estimation of flow. Permit holders are now required to estimate discharge flow from their sites as well as the flow in the stream or river (described as the receiving water in the permit) the discharge flows into. Ecology needs these flow estimates to better understand the potential for impacts to receiving water quality.

The purpose of this guide is to provide permittees with detailed descriptions of a few of the easiest or most common methods for taking flow measurements, if they choose to manually collect the data on their own. The intent is to assist permittees in understanding how to meet the permit requirements in a manner that is simple yet also accurate enough to meet Ecology′s needs. Other methods, not described in this guide, such as hydrologic models, in-pipe flow meters, calculations based on pump usage, automated flow devices, and others could also be used. Any flow estimating method that meets the intent of the permit would be accepted by Ecology.

The methods presented may not be useful in every situation. In some cases, permittees may require technical assistance because of time constraints, site complexities or equipment requirements. Skilled professionals could also provide advice on additional techniques not covered in detail here.

It is important to note that the permit requires the estimation of "receiving water" flow. In simplest terms the receiving water is the stream or river your site′s stormwater or process wastewater discharge flows into. However, in some cases it can be difficult to distinguish a natural receiving water from a drainage ditch. A definition and some criteria for determining what constitutes an official receiving water is provided in the following section.