Selected Water Quality Processes in Rivers and Streams - Hydro-Environmental Analysis: Freshwater Environments - page 142

Headwaters Tr ansfer

Deposition

Mean flow velocity

Drainage area (~downstream distance 2 )

FIGURE 5.15 Longitudinal changes in river characteristics. (From FISRWG, Stream Corridor Restoration:
Principles, Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)

departments, conservation districts, and many state water quality and forest management
agencies.
Another devastating type of sediment low is debris low. Generally with sediment transport,
the concentrations of the sediment are low enough that they do not dramatically alter the char-
acteristics of the low. In particular, sediments do not impact the Newtonian luid properties. For
Newtonian luids, the relationship between stress and strain is linear, where the proportionality
constant is the viscosity or “thickness” of the water. For a non-Newtonian luid, the thickness
varies with the applied stress. Another result is that water will continue to low, while if a non-
Newtonian material moves it may leave a hole behind. In hyperconcentrated low, such as when
large volumes of sand are transported in suspension, the amount of suspended sediment is suf-
icient to change the luid properties and sediment transport mechanisms. Hyperconcentrated
low can be highly erosive. In debris low, the sediments and water form a slurry capable of
holding large particles and even boulders in suspension (Figure 5.16), and the impacts of these
mud slides may be catastrophic (Costa 1988; Jakob and Hungr 2005), destroying bridges, cul-
verts, roads, and aquatic habitats. Debris lows can occur, for example, from a rainfall event on a
burned area, following liquefaction of hillsides, or volcanic eruptions such as Mount St. Helens
(see Figure 5.17).