RFP2773 - Stage 2 - Jonas Street Stormwater Upgrade

Timaru District Council completed a stormwater assessment of the Jonas Street / Grasmere Street catchment to address flooding at 41 Grasmere Street. The assessment identified pipe capacity constraints, network surcharging, and inadequate inlet performance, resulting in significant overland flow during storm events. Option 1 from the pipe performance assessment has been adopted, involving a new stormwater pipeline along Grasmere Street and upstream network upgrades to reduce surcharging. However, flooding is primarily driven by insufficient inlet and sump capacity, with flows exceeding 300 L/s, making inlet capacity the critical design constraint.