Abstract

Following the February 2004 flood the Otorohanga District Council (ODC) has commissioned Environment Waikato to undertake investigation of the flooding risk at the primary school, which experienced flooding during the event and recommend measures to reduce the risks.

A report on the causes of the flooding at the primary school has been carried out for Trevor Skilton of ODC. This report was based on local knowledge and indicated the existence of overland flows from the Waipa River over the right bank some 5.0km upstream of the primary school. These overflows plus the local runoff flowed through internal drains (Waipa and Rangiatea drains) and over farmland, have caused flooding of the primary school before discharging into the Waipa River.

Following the preliminary investigation, it was agreed that further investigation including hydraulic modelling was required. In order to develop the hydraulic model ODC undertook a survey for the Rangiatea Rd including ground levels at the overflow location, flood levels along Rangiatea Rd and cross sections of the local drains.

This report provides the findings of the hydraulic model which has been developed and calibrated using the information provided by ODC, existing river cross sections and gauge data. It also investigates the effectiveness of different flood relief measures, which need to be considered by the District Council.

Waipa River - Otorohanga Primary School Modelling Report [PDF, 136 KB]