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Sediment Delivery

Figure 1.  A 1939 aerial photograph of an old growth forest in the Olympic Peninsula, Washington, shows how a very large storm (1934) triggered numerous debris flows at the heads of first order streams. Most of the debris flows traversed through headwater (first and second order) streams and deposits sediment and wood in higher order fish bearing streams (from Benda et al. 1998). This type of watershed has high connectivity - sediment delivery.
Figure 2.  An example from an old growth forest in the Oregon Coast Range (right panel) shows accumulations of large logs that was deposited by a debris flow at the mouth of a second order streams; see also Bigelow et al. 2007.
Figure 3. Stand replacing fires in the Tillamook basin, Oregon Coast Range, in conjunction with large rainstorms triggered numerous shallow landslides and debris flows (from Benda and Dunne 1997a). Wildfires can increase the connectivity between hillslopes and streams.
Figure 4. An extreme example of poor road building, widespread clearcutting and a large storm yielding numerous debris flows that deposited sediment and organic material into fish bearing streams (in northwest Washington). This highly dissected landscape has great potential for very high connectivity, particularly following the destabilizing effects of road construction and timber harvest.
NetMap contains a tool for predicting debris flows and their potential ecological impacts on streams and rivers.
In this model, there are two types of source areas for large wood to fish bearing streams and rivers:
1.     hillslope areas that trigger debris flows that travel to fish-bearing streams, and
2.     steep headwater channels that are traversed by debris flows prior to depositing in lower gradient, fish bearing channels.
Learn more about NetMap's sediment delivery predictions.
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