Rivers and Streams, Characteristics - Hydro-Environmental Analysis: Freshwater Environments - page 27

To pographic floodplain
Hydrologic floodplain

Bank-full width

Bank-full
elevation

Bank-full depth

FIGURE 2.15 Lateral variations in the channel and loodplain. (From FISRWG, Stream Corridor
Restoration: Principles, Processes, and Practices , Federal Interagency Stream Restoration Working Group,
1998.)

are transported as individual particles and some of the ine materials that may form locs, so their
transport is also determined by the other particles around them.
In rivers with moderate slopes, there are basically two types of transport (MacArthur et al. 2007):

• Bed load plus suspended load

• Bed load plus wash load

In the irst, the suspended load is the particles that are small enough to be kept in suspension by
the turbulence in the river and the bed load is the coarser particles that are transported along the bed
intermittently by rolling, sliding, or saltating (bouncing along the bottom). In the second, the bed-
load material includes all types of solids found in the bed whether they are transported in the bed or
in suspension, and the wash load is the ine particles traveling in suspension that are not commonly
found in the sediments. The suspended load is carried by the low, so it travels at the same velocity,
while the bed-load transport may differ from the dominant low velocity and may only occur during
high-low events.

2.2.1.5 River Continuum Concept
The best-known longitudinal model for rivers is the river continuum concept (RCC) (Figure 2.16),
irst proposed by Vannote et al. (1980), which attempts to generalize and explain the observed lon-
gitudinal changes in stream ecosystems.
The RCC model proposes that (FISRWG 1998):

• Rivers exhibit continuous longitudinal changes in their physical characteristics from their

headwaters to their mouth

• The longitudinal gradient in their physical characteristics controls the biotic response

Therefore, the RCC model identiies relationships between the progressive changes in a stream's
structure, such as the channel size and streamlow, and the distribution of species. So, the biotic
response is then not just a function of some physical characteristic, such as temperature, but the
position (location) along the length of the river.
Longitudinal connectivity refers to physical changes along the entire stream and the chemical
and biological responses to those changes. For example, a headwater woodland stream (Orders I-III)