Environmental Engineering Reference
In-Depth Information
The increase in paved surfaces has been spurred on not only by urban and suburban
development, but also by a steady increase in the use of automobiles, the primary mode
of daily transportation. According to a 1999 study, motor vehicle infrastructure, such as
roads and parking lots, accounts for close to half of the land area in U.S urban cities
(GAO 2001). There have been numerous studies completed since 1994 on the issue of
watershed protection techniques, examining the relationship between stream quality and
watershed urbanization. In general, these studies point to a deterioration of steam quality
with increasing urbanization, e.g. it has been estimated (Paul & Meyer 2002) that a
threshold exists at about 10% impervious cover, after which sensitive elements are lost
from the aquatic system. As presented in the previous chapter, a well-defined trend of
increased nutrient loading with the increased level of urbanization was established in the
Lake Chivero basin as well. The increase in impervious surfaces alters the hydrology and
geomorphology of streams and results in predictable changes in stream habitat. Common
effects
are: decline in biodiversity, reduced DO concentrations and increase in invasive
species (Paul & Meyer 2002, Gromaire-Mertz et al. 1999). Below is a summary of the
most common impacts of impervious covers.
• Hydrologic impacts
Increased runoff;
Increased peak flow, due to increased velocities in hydraulically more efficient
drainage channels;
Increased bank full flow;
Decreased base flow;
• Physical impacts
Changes in stream geometry (channel enlargement);
Increased stream meandering;
Alteration of stream channel networks (through channel modification) and barriers
to fish migration;
• Biological impacts
Effects on aquatic insect diversity, wetland diversity and fresh water aquatic
ecosystem diversity asa whole.
In many countries of the region, the storm drainage system is treated like the commons,
free for anyone to pollute with little risk of being caught and little awareness by the
general public that they may be polluting. Niemczynowicz (1999) points out that the
long-term cumulative effect of storm water runoff on our fragile urban water environment
and the catchment water resources is severe and cannot be ignored. In order to provide
for a safe beneficial use (potable, recreational, agriculture, etc), a proper management
approach of the catchment area, based on the characterization and quantification of water
needs and pollution fluxes, is necessary. Pollution prevention, impact minimization,
assessment of assimilation capacity and management of the symptoms of pollution are
required for catchment storm water quality planning. The possible effects of increased
storm water pollution should be considered at the planning stage of urban development
