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Chapter 2 Literature Review
Thermal Pollution Due to Urbanization
Urbanization is the product of a growing and developing population. An alteration of land cover is inevitable with this new development. The natural cover of watersheds is replaced with expanses of impervious surface. Klein (1979) discovered a trend where observed water temperatures rise in watersheds with increasing impervious cover. These impervious surfaces, especially without canopy cover, absorb heat much faster than any natural cover. While experimenting with thermal characteristics of stormwater runoff, Thompson et al. (2008) found asphalt to be particularly good at absorbing and storing thermal energy. An average temperature of 43.6°C for asphalt was reported versus an average temperature of only 23.3°C for turfgrass sod under the same conditions. Thompson and Wilson et al. (2008) reported an average runoff temperature from an asphalt parking lot for 15 events to be 29.8°C. A hydro-thermal model to quantify the impact that urban development in cold water stream watersheds has on stream temperature was created by Janke et al. (2009). It was stated that the runoff from a 0.58 acre parking lot during a mid-August rainfall event of only 0.33 cm produced a heat export of more than 250 MJ when related to a temperature of 20°C. That heat energy would be the equivalent received by a stream with a normal temperature of 20°C if the runoff was totally unmitigated. It has been determined that high initial pavement temperatures pose the greatest risk of thermal impact on the receiving stream. This scenario is most likely to occur during late summer and early fall when afternoon or early evening rainfalls occur after hot, dry days. Altering the slope or dimensions of parking lots is not enough to remedy the thermally charged runoff because it has been found by Herb et al. (2009) that altering these parameters by ±20% produced less than 1°C change in runoff temperature.
Impacts on Cold Water Streams
Coldwater streams are a unique habitat that are being encroached upon and degraded by increasing urbanization. A coldwater stream is defined as a stream that supports trout and other coldwater fish species according to Eaton et al. (1995). These ecosystems support a range of thermally sensitive organisms. Wang and Kanehl (2003) found that the most important environmental factor that affects assemblages of cold water macroinvertebrates in urbanizing watersheds is the percentage of urban land use in the watershed. Macroinvertebrate populations suffer greatly once impervious levels in a watershed exceed 10 percent. The impervious threshold decreases 1-2 percent for cold water streams compared to warm water streams, meaning that cold water streams are more prone to damage by low level urban development. It was also stated that water temperature is at least
as important as urban land use when looking at the effects of urbanization on assemblages of macroinvertebrates in cold water streams. Trout are native to cold water streams throughout the United States. They are very sensitive to abrupt temperature changes. Coutant (1977) found that trout prefer to avoid water
temperatures exceeding 21°C. Once temperatures rise above that level, mortality rates begin to increase according to Lee (1980). A study by Matthews et al. (1994) showed that trout tend to occupy a temperature range between 12.8°C and 19.1°C. Edwards et al. (1979) stated that temperature not only influences mortality in trout species, but it also affects feeding, spawning, overall health, and growth. It has been observed by Matthews et al. (1997) that
trout will actually select cool water, even if it is low in oxygen. This suggests that thermal pollution remediation in developing cold water stream watersheds is significant to protecting sustainable trout fisheries. The Commonwealth of Virginia regulates water temperature based on seven water types.The maximum allowable temperature listed for trout sensitive waters is 21°C, and limited to only 20°C in natural trout waters. In addition, the Virginia Code regulates a maximum rise above the natural temperature and a maximum hourly temperature change for point sources. The maximum rise above the natural temperature in not permitted to exceed 3°C, and for Class VI waters (natural trout waters) it cannot exceed 1°C. The maximum hourly temperature change is not permitted to exceed 2°C, and for Class VI waters (natural trout waters) cannot exceed 0.5°C. Table 2.1 is taken from 9VAC25-260 Virginia Water Quality Standards, Statutory Authority: § 62.1-44.15 3a of the Code of Virginia.
List of Figures
List of Tables
1 Introduction
1.1 Background
1.2 Problem Statement
1.3 Objectives
2 Literature Review
2.1 Thermal Pollution Due to Urbanization
2.2 Impacts on Cold Water Streams
2.3 BMPs
2.4 Summary
3 Methods
3.1 Site Selection
3.2 Bioretention Site Specifications
3.3 Materials and Methods
4 Results and Discussion
5 Conclusions
5.1 Conclusions
5.2 Future Work
5.3 Final Words
Bibliography
Appendices
Appendix A: Temperature and Flow Data
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Thermal Pollution Mitigation in Cold Water Stream Watersheds Using Bioretention
