Where is the most effective location for buffers in a watershed?

Continuously on both sides of the channel in the upper portion of the watershed.

The function of buffers is to intercept nonpoint source pollutants from upland agricultural systems. To be most effective streams that are in closest contact with the uplands should be buffered. In any landscape there are ridges and valleys. In the agricultural landscape water, sediment and chemicals can move as surface runoff to the valleys.Where the slope distance (distance between the ridge and the channel) is the shortest the valley probably contains an ephemeral channel or gully (one that only carries water during a rain event and has no contact with the local water table). That ephemeral channel or gully may actually not exist because a grass waterway has been installed as a best management practice. As the slope distance increases the valley will contain intermittent (runs only during the wet season of the year) and perennial (runs year round) channels. These channels are in contact with the water table that are the first actual stream channels to receive sediment and chemicals from the upland.

On a watershed basis, these small (first - third order) streams are included in the zone of sediment and nutrient production and these are the channels that should be buffered first. Larger streams function primarily as transport channels for the flow that has been collected by the smaller streams. The volume of water and sediment supplied directly from their adjacent uplands is small compared to the volume of water that is contributed from upstream.

Randomly locating buffers along streams with little continuity can provide effective field-level reductions of NPS pollutants but will have little measurable effect on stream water quality. While any buffer has value they are most effective for stream water quality improvement when they are installed using a watershed approach.