Ch 07 - Rivers and Flooding
Answers to Review Questions and Critical Thinking Questions
1. The drainage basin is the area drained by a single stream or stream
2. Total load includes bed load, suspended load, and dissolved load
3. The continuity equation, Q=WxDxV, governs the accommodation of water
flow in stream channels.
4. The principal lessons learned from the Ventura River flood are that
it is important to assess the historical behavior of a river and to adjust
engineering models accordingly.
5. Competency is the largest particle a stream can transport, while capacity
is the total mass of sediment a stream can transport.
6. Braided channels are multiple, relatively straight, channels separated
by bars and islands, while meandering channels are single, winding channels
with diverse habitats.
7. The riverine environment includes the channel and adjacent floodplain,
both of which are utilized by the river.
8. Pools are deep, slow-moving parts of the channels, while the riffles
that join them are shallow and relatively fast moving.
9. Upstream floods affect the upper portions of drainage basins and typically
result from intense storms of short duration. Downstream floods affect
broad portions of the lower portions of drainage basins, are typically
of longer duration, and result from widespread storms of lesser intensity.
10. The 10-year flood has a 1/10 chance of occurring each year. On average,
the 10-year flood should occur once in 10 years.
11. Urbanization affects the flood hazard by increasing impermeable surfaces
and serving greater areas by storm sewers; these factors increase the
severity of low and intermediate frequency floods.
12. The major factors that control flood damage area land use on the floodplain,
the magnitude and frequency of flooding, the rate of rise and duration
of flooding, the season in which flooding occurs, the sediment deposited,
and the effectiveness of forecasting, warning and emergency systems.
13. Primary effects of flooding include injury, death, and damage to farms,
buildings, railroads, etc. Secondary effects include short-term river
pollution, hunger and disease, displacement of populace, and fires.
14. Floodplain regulation strives to obtain the most beneficial uses of
floodplains while minimizing flood damage and the cost of protection.
Methods include zoning, flood hazard mapping, and, in some cases, construction
of modest flood prevention structures.
15. Channelization is the engineering of a channel to minimize flood hazards
for an area, using methods of structural flood controls, wetland draining,
erosion control, and improvement of navigation.
16. Channel restoration includes a series of techniques to reestablish
natural processes in stream channels that have been degraded.
Critical Thinking Questions
1. The plan of action should include assessment of the permeability of
existing surfaces in the basin, an assessment of the impacts of development
density on permeability, a determination of the likely increase of flood
hazards, and a set of strategies for minimizing the impacts of the urbanization
on the stream.
2. The plan should include an assessment of the physical condition and
processes of the existing stream, and strategies that work with natural
river processes to restore stream features that are aesthetically pleasing
and help reduce the hazards of flooding.