Effectiveness of Wastewater Collection System Rehabilitation to Reduce Infilration and Inflow Feb 2004

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rehabilitation and nine for the post rehabilitation for comparison. Criteria for storm selection included: 1. No wastewater collection system overflows. Overflows would corrupt the volume and peak response to rainfall comparison. 2. Storms occurred between November and April during winter, relatively wet soil conditions. 3. If possible, storm was preceded by one to two dry days to reduce the influence of previous storm events on the data . 4. Only smaller storms of less than two-year events (2.9 Inches of rain in a 24-hour time period) were selected. Overflows or basement backups could potentially have occurred in response to larger storms potentially affecting the data validity. In addition, the flow monitoring equipment was generally less reliable during large events. Figures 8 through 11 present the results of the event effectiveness assessment for the Amazon Basin. The event analysis includes a comparison of event, 7-day, and 3-day volume as well as a peak event flow rate versus maximum event rainfall intensity. The event volume analysis shows an RDII reduction effectiveness of 40%, 39%, and 29%, for the comparison with event, event plus 7-day, and event plus 30-day rainfall, respectively. This is logical because longer antecedent periods include larger periods of "normal" (non- RDII dominated periods) that tend to reduce the overall percent difference. It could also indicate that the RDII due to previous (8-30 days) rainfall has not been reduced as much as the RDII from the immediate rainfall and from rainfall during the previous 7 days. The event peak analysis shows a reduction of 35%, indicating a significant reduction in inflow or fast response sources. Although, there is a very low correlation between peak flowrate and event peak intensity of rainfall in the pre-rehabilitation basin, visual inspection of shows a marked decrease in peak flow rate across the range of peak rainfall intensity.