DETERMINING REHABILITATED SEWER FLOW CAPACITY

The flow capacity of existing sanitary and storm. sewers is a signific ant issue when making decisions on the optimal method of rehabilitatio n. At times the resulting flow capacity is an important factor during the design of a sewer rehabilitation program. Tn the United States, th e flow capacity is usually determined using the Manning formula, which includes the empirical parameter n. This committee report discusses t he principal elements of the Manning formula, coefficient and field va riables that contribute to the selection of values for n, and provides typical values for n for mature sewers in need of rehabilitation and for mature sewers rehabilitated with many currently available rehabili tation materials. The report then discusses a rationale for selecting a design n within a range of values and predicting the resulting chang e in dow capacity of the sewer. A field example is given where n value s were measured. The report is intended to provide guidance to enginee rs making decisions related to rehabilitation of gravity flow sewers.