U.S. cities with com­bined sew­er sys­tems risk hav­ing those sys­tems over­whelmed dur­ing flood­ing, lead­ing to the release of untreat­ed sewage, accord­ing to an arti­cle in Eura­sia Review.

Com­bined sew­er sys­tems col­lect stormwa­ter and sewage using the same pipes, dis­charg­ing their con­tents at waste­water treat­ment plants. “But the pipes can only con­vey a cer­tain amount of flow. Dur­ing wet weath­er events, to avoid inun­dat­ing the waste­water treat­ment plants some por­tion of the flow still over­flows into the nat­ur­al water bod­ies through fea­tures known as com­bined sew­er over­flows – or CSOs.”

While cities are work­ing to upgrade their infra­struc­ture and lim­it CSOs, “As cli­mate change brings more heavy rain and high­er riv­er lev­els, the prob­lem wors­ens and can­not be mit­i­gat­ed with con­ven­tion­al approach­es to stormwa­ter man­age­ment.”

A group of researchers from Drex­el Uni­ver­si­ty study­ing Cam­den, New Jer­sey cre­at­ed cli­mate mod­els to sim­u­late future flood­ing and CSOs in the city and eval­u­ate the effec­tive­ness of poten­tial inter­ven­tions. Using the mod­el, researchers found that a pro­pos­al to divert upstream stormwa­ter away from its sew­er sys­tem could help reduce CSOs. “Over­all, the results sug­gest that increased pre­cip­i­ta­tion events due to cli­mate change will cause more com­bined sew­er over­flows. And sea lev­el rise will make it more dif­fi­cult for these sys­tems to dis­charge into near­by bod­ies of water.”