Flood management

MNV carries out a range of flood management work including catchment management, flood risk assessments, flood monitoring, post flood surveys and the operation of flood warning systems. We work closely with communities, individual landowners and flood prevention authorities.

We take an integrated approach so that the causes and effects of flooding are considered and where possible flood management has wider benefits for communities and landowners. This involves looking more widely than just the flooded site, to investigate where the flood originated, see whether the runoff rates and flows in rivers are un-naturally rapid, whether there are opportunities for natural storage in the catchment and whether there has been inappropriate developments on the floodplain or close to the river.

Catchment management planning
Working with landowners, communities and agencies we develop short term and long term plans for managing flood water in the agricultural, forestry and urbanised areas within a catchment. Flood water is stored in natural systems such as wetlands and released slowly into the rivers. The rivers are then restored with natural features such as meanders to slow down the flow rates in the channels. This approach makes a significant difference to reducing flood risk downstream.

Flood risk assessments
We carry out flood risk assessments for developments close to rivers. This involves a detailed survey of the river channel, the floodplain, development site and any structures such as bridges or roads. The survey data are imported into a hydraulic model which is run with a range of flood flows including the 1 in 2, 1 in 100 and 1 in 200 year flood events. The extent and depth of the flood water is determined and so the risk of flooding is assessed.

Community flood plans
We work closely with rural communities to reduce the risk of flooding and to ensure the community is prepared for flood incidents. This includes the provision of temporary flood defenses, provision of flood warning systems, strategic flood risk assessments and individual property flood risk assessments.

Post flood surveys
We survey areas which have suffered flooding to accurately determine the flood levels and to investigate causes and possible remedies. These surveys can include taking levels of trash marks which can provide evidence of the maximum water levels and depths. They can also be used to estimate the maximum flows in a particular flood event. We work closely with communities to gather evidence from past flood events using simple techniques such as fixed point photography.

Flood warning
We operate flood warning stations which automatically trigger alarms when critical levels are reached. The stations can be installed on big river, small channels, upstream of culverts or in lakes and reservoirs. Water levels can be read at intervals of 1 minute to 1 hour and the data either transmitted at regular intervals or an alarm raised when a certain level is reached.