Environmental Engineering Reference
In-Depth Information
TABLE 8.1
Project Intent Information for All NRRSS Nodes
Expenditure
(millions of
dollars)
Number of
Projects
Project Intent
Water quality management
4816
2374
Floodplain reconnection
323
1984
Flow modiication
476
1645
Riparian management
5141
1468
Aesthetics/recreation/education
1131
1463
Channel reconiguration
557
1358
Bank stabilization
2546
925
Instream habitat improvement
2292
922
Stormwater management
536
727
Dam removal/retroit
468
549
Land acquisition
247
541
Instream species management
369
449
Other
759
292
Fish passage
859
122
Source: National River Restoration Science Synthesis Database,
from March 28, 2006.
Central United States, Chesapeake Bay, Paciic Northwest, Southeast, Southwest, and Upper
Midwest. The goals of the NRRSS were to summarize restoration trends and assess project effec-
tiveness. The most common types of projects and costs (for those projects where the intent and costs
were speciied) are illustrated in Table 8.1. One result of this compilation and analysis was that only
10% of the projects that were reviewed had documented any form of project monitoring, and little if
any of that information was either appropriate or available for assessing the ecological effectiveness
of the restoration activities (Bernhardt et al. 2005). The lack of monitoring often precludes deter-
mining whether restoration projects actually achieve their design goals.
8.2 ANTHROPOGENIC IMPACTS
Historically, much of river management was based on the alteration and control of rivers and streams
for human beneit, rather than maintaining their ecological integrity. For example, the traditional
management paradigm for lows was based on how much water could be taken out of a river, rather
than how much should be left in (Hirsch 2006). Rivers were controlled to reduce looding and were
altered for some speciic purpose, such as channelization for navigation, agricultural abstractions, etc.
As stated by Boon (1992): “rivers have been abstracted from, ished in, boated on, discharged into;
their headwaters have been diverted; their middle reaches dammed; their loodplains developed.”
Examples of common engineering modiications (Soar and Thorne 2001) include:
Resectioning: Designed to alter the cross section to increase the in-bank discharge capac-
ity. This is usually accomplished by enlarging the cross-sectional area and/or elevating the
slope, usually by dredging and widening. Resectioned rivers are commonly trapezoidal
and wider and deeper than natural rivers. Resectioned rivers also usually require mainte-
nance, such as dredging, and stabilization of their banks, such as by using riprap.
Realignment: Usually included in resectioning, realignment involves straightening riv-
ers and increasing the slope of the bed, or bottom, in order to increase the low velocity.
 
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