Step 2: Characterize Your Watershed (cont.)

Estimating Pollutant Loads
Early in the watershed characterization process, you identified and gathered available data and information to assess the watershed and created a data inventory. Then you conducted a preliminary data review, identified gaps, and collected additional data if needed. Finally, you analyzed the data to characterize the water body conditions and identify causes and sources. Your next step is to estimate pollutant loads from watershed sources to target future management efforts. This step satisfies element b of the section 319 guidelines.

Without knowing where the pollutants are coming from, you cannot effectively control them and restore and protect your watershed. The loading analysis provides a more specific numeric estimate of loads from the various sources in the watershed. By estimating source loads, you can evaluate the relative magnitude of sources, the location of sources and the timing of source loading. The loading analysis can help you plan restoration strategies, target load reduction efforts and project future loads under new conditions.

You can use various approaches to do the loading analysis, and which one is right for you depends on several factors, including water quality parameters, time scale, source types, data needs, and user experience. Some loading analyses are focused on determining how much load is acceptable, whereas others focus on source loads that attribute loading to each category of sources in the watershed. For watershed planning purposes, source load estimates are desirable because the information can be used to support management planning and targeting of restoration resources.

Sometimes loading estimates have already been developed for watersheds. Check whether a previous study is available—a total maximum daily load (TMDL); a USGS, USDA, university, or Clean Lakes study; or other watershed-based program that might have required development of loading estimates. Such studies can often be used to provide loading estimates appropriate for developing the watershed plan.

Two general types of techniques are used for estimating pollutant loads. The first type is a set of techniques that directly estimate loads from monitoring data or literature values. These techniques are best suited to conditions where fairly detailed monitoring and flow gauging are available, and the major interest is in total loads from a watershed. The second type is watershed modeling techniques. These techniques include a wide range of models that can provide loads by sources, help predict future conditions and evaluate multiple management practices.