Environmental Engineering Reference
In-Depth Information
reservoirs, are applied. Greentree reservoirs are shallow, forested flood-plain impoundments usually
created by building low levees and installing outlet structures. They are usually flooded in early fall and
drained during late March to mid-April. Draining prevents damage to over-story hardwoods (Rudolph
and Hunter, 1964). Most existing green tree reservoirs are in the southwestern U.S. The green tree
reservoirs provide habitat for many animal species. The flooding of green tree reservoirs differs from the
natural flood regime. Green tree reservoirs are typically flooded earlier and at depths greater than would
normally occur under natural conditions. Over time, modifications of natural flood conditions can result
in vegetation changes, lack of regeneration, decreased mast production, tree mortality, and disease.
Proper management of Green tree reservoirs requires knowledge of the local system-especially the
natural flood regime and sediment transport and deposition.
Figure 10.55 shows an artificial wetland in the suburbs of Seoul, South Korea. Many birds have colonized
the new habitat just a few years after the artificial wetland was created. In the meantime the wetland also
attracts tourists.
Fig. 10.55
An artificial wetland in the suburbs of Seoul, South Korea
Is it certain that the species richness, number density, and other biodiversity indices of benthic
invertebrates and fish will increase if river-linked riparian lakes or wetlands are created? A comparative
study was performed to answer these questions with samples taken from a river-lined lake—Zengjiang
Bay, a low flow area of the Zengjiang River channel at Zhengguo, and an isolated riparian lake—
Xizhijiang Oxbow Lake in the East River basin (Wang et al., 2008). Figure 10.56 shows the geographical
locations of Zengjiang Bay, Zhengguo, and Xizhijiang Oxbow Lake. The Zengjiang River is a tributary
of the lower reaches of the East River. Substrate in the main channel of the Zengjiang River consists of
sand. No benthic invertebrates were found in the sample from the river at Zhengguo.
Zengjiang Bay is like a riparian lake with a 100 m wide outlet connecting the river. The river carries
fine suspended sediment into the bay which is deposited there. A mud layer covers most of the bay, and
some hydrophytes have colonized parts of the bay. The flow velocity and water depth in the bay vary in
the range of 0-0.5 m/s and 0-3 m, respectively. Zengjiang Bay provides multiple habitats for benthic
invertebrates. The species richness of samples taken from the bay is 31, and the abundance of individual
invertebrates is 343 ind/m 2 . The calculated Shannon-Weaver index and bio-community index are H =
2.58 and B 15.05, both the highest value in the East River. There are many fish species in the bay.
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