Environmental Engineering Reference
In-Depth Information
2.2.2.3.1 Terrace Formation
Terraces are the lat-topped (benches) remnants of abandoned loodplains, formed through the
interplay of incising and loodplain widening. The Federal Interagency Stream Restoration
Working Group (FISRWG 1998) provided an example of terrace formation by channel incision (see
Figure 2.24):
Cross-section A represents a nonincised channel.
Due to changes in the streamlow or sediment delivery, equilibrium is lost and the channel
degrades and widens.
The original loodplain is abandoned and becomes a terrace (cross-section B).
The widening phase is completed when a loodplain evolves within the widened channel
(cross-section C).
Nonincised stream
Surface 3
Hydrologic
floodplain
Te rrace
Surface
1
Bank-full channel
(a)
Incised stream (early widening phase)
Surface 3
Hydrologic
floodplain
Te rrace
Surface
1
(b)
Incised, widening channel
Incised stream (widening phase complete)
Surface 4
Te rrace
Hydrologic
floodplain
Sur f ace
3
Surface
2
Surface
2
Surface
1
Bank-full channel
(c)
FIGURE 2.24 Terraces in (a) nonincised and (b,c) incised streams. (From FISRWG, Stream Corridor
Restoration: Principles, Processes, and Practices , Federal Interagency Stream Restoration Working Group, 1998.)
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