Principal Investigator: James R. Wallace (Georgia Institute of Technology)
Sponsor: GWRI
Start Date: 1969-10-01; Completion Date: 1971-09-30;
Keywords:
Description:
A complete analysis of the relative potential utility of alternative flood plain management techniques must include an examination of many interrelated aspects of urban flooding. For example, the hydrologic aspects of the flood problem are influenced by the land-use pattern that develops with urbanization, and the land-use patterns are a reflection of the social values and economic needs of the community.
In order to examine the relationship between the pattern of land use and storm runoff, the development of the Peachtree Creek watershed in metropolitan Atlanta, Georgia, was traced for a period of ten years and the influence of the development on streamflow was analyzed. During the period of analysis (1949-1968), the percentage of the watershed surface covered by impervious area increased from 17.13 to 31.21, an increase of about 12,000 acres. During the period 1949-1955 dense development occurred primarily along the rail lines and principal city thoroughfares. The rail lines and thoroughfares are predominantly located on ridge lines, and the earlier development was concentrated at the extremities of the watershed. During the period 1955-1968 the most significant changes were located in the vicinity of the newly constructed interstate highway system which paralleled the entire length of one of the major forks of the creek. Hence, the most recent development has been located very near the creek, and in some cases within the flood plain.
The affect of this development on the hydrology of Peachtree Creek was determined by comparing runoff from Peachtree Creek with that of an adjacent control watershed and by analysis of storm hydrographs. It was found that the average storm runoff per square mile from the major storms during the months of August and September for the period of 1963-1969 was approximately three times that which occurred during the same months for the period 1959-1963. On the other hand, the wet season base flow from the non-urbanized control watershed has been about 1.46 times as great as the base flow from Peachtree Creek. Thus, it seems clear that urbanization has affected the seasonal
distribution runoff. However, the hydrograph analysis showed no systematic trend in unit hydrographs derived from winter (wet season) storms during the period of record. This is consistant with the fact that no significant increase in the volume of direct runoff, as compared to the control watershed, occurred during the period of record. The overall implication of the study is that the development of the watershed has increased storm runoff in the dry months, decreased base flow in the wet months, and significantly increased the peak runoff from summer storms. Such a trend, if continued, could result in an extended “flood season” in which large flood peaks could become as common in the summer months as they have historically been in the winter and spring.