25 October 2004
Monitoring Strategies. A variety of techniques are available to monitor the
effectiveness of LID features for managing water quantity and quality. A well-
implemented monitoring program will be valuable not only for the purpose of local runoff
management objectives, but can also provide useful information to the Engineering
Service Center, which is developing a web-based expert system.
5-5.2.1 Water Quantity Monitoring. The effectiveness of LID in controlling runoff
volume and peak flow rates can be monitored either at individual features on a site or at
some selected point downstream where flow paths converge and a measurement
device can be installed.
5-22.214.171.124 Small Scale. On a small scale, both manual and automatic sampling
methods can be used to calculate flow rates upstream and downstream of an LID
installation, based on the depth measured using a weir or a rate of flow measured using
a conveyance device.
5-5.2.2 Large Scale. On a larger scale, where LID features are used as retrofits in
developed areas, the effectiveness of the retrofits can be assessed by comparing pre-
LID and post-LID flow rates downstream. Using these data and some straightforward
hydrologic calculations, a characteristic hydrograph can be developed to evaluate the
site's response to storm events resulting from the implementation of LID treatments.
Data from stream gages should indicate that runoff from smaller storms has decreased
after LID implementation. As more LID features are used for stormwater retrofits on a
site, the decrease in runoff will become more significant.
5-5.2.3 Water Quality Monitoring Parameters. The effectiveness of a runoff
management feature can be evaluated using the flow through the feature, the quality of
the receiving waters, or both. The Nationwide Urban Runoff Program (NURP) has
identified the following "standard pollutants characterizing urban runoff:"12
Table 5-1. Standard Pollutants in Urban Runoff
Suspended Solids Concentration
Biochemical Oxygen Demand
Chemical Oxygen Demand