Natural Flood Management Aerial Survey

Aerial Survey of the Natural Flood Management Scheme at Mill Green Farm, Debenham

CLIENT Water Management Alliance (WMA), East Suffolk IDB
As part of the holistic water management plan for the river Deben catchment, WMA engaged RAS Ltd to provide a full GPS calibrated topographical and video survey of the area around Mill Green Farm.

Debenham is located at the convergence of three tributaries that carry storm water from an extensive catchment to a narrow river running through the village. The EA had previously looked at large engineering projects to alleviate the problem. Flooding in 2012 focused minds on creating a cost-effective solution based around Natural Flood Management (NFM). The aim of the project is to reduce flood risk to properties in Debenham by attenuating flood flows in the upper catchment.

The Mill Green NFM feature is one of four features that work together to alleviate the risk of flooding in Debenham.  WMA proposed an embanked on-stream attenuation pond that could store an additional 7,000+ m3 of storm water.

Remote Aerial Surveys by RAA Ltd was asked to map the site for a topographic survey, and to capture aerial photography and video to report the progress and show the completed scheme.

To develop the scheme and get the required approvals Pete Roberts, WMA’s Operations Engineer, needed to know the lie of the land, opting for a drone survey as; “video surveys give us great visual capture of the works. Pre- and post- footage shows us how the site has changed.”

RAS Ltd was selected from a number of companies who quoted for the work, based on their response and competitiveness.

“RAS helpfully interpreted the specification and came back with exactly what we asked for. They clearly paid attention, and highlighted some additional benefits,” Pete explained.

RAS used an unmanned aerial vehicle (UAV) flying a 20MP camera with stabilised and vibration free mounts to take the high-quality video surveys, and returned a number of key deliverables:
• A detailed Digital Terrain Model <20mm (x,y); <30mm (z)
• Cross Sections spaced 25m from each other
• Long sections
• Orthomosaic
• 4K video footage
• Plus a flight report

Data that would have taken days to manually collect, download, process and draw up, was available far quicker with video footage that Pete Roberts says is “brilliant for taking to public presentations and gaining acceptance for such plans.”

WMA used the footage supplied by RAA Ltd during the planning stage to gain approval for the storage pond. It was also key during construction in Autumn 2018.

The new embanked on-stream attenuation pond has reduced the risk of flooding in Debenham. In normal conditions it occupies an area of 11,164 m2, storing up to an additional 7,027 m3 of water in flood events. When water levels rise by 0.5 m the water body expands to cover 16,947 m2.

Using Natural Flood Management has helped address local issues while protecting the environment. Additional amenity benefits from the new wetland habitat will become a popular amenity feature within a farm trail created by the farmer who donated the land.


When public money is being used, driving the maximum benefit from investment is vital. Communicating the impact and value of NFM schemes to diverse groups of people like residents, farmers, councillors, etc. was faster and more cost-effective using aerial video. It helps to establish how the local area will benefit – gaining buy-in and winning hearts and minds.

“RAA Ltd are very good people to work with. They are professional throughout the whole process. From their response to the spec, the experienced pilot on the day and deliverables that met our quality requirements. Turnaround was very quick and hit the deadlines to put the data into our overall design package. As remote aerial technology races on, it’s great to be part of the technology curve and take advantage of everything it offers.”

Pete Roberts, Operations Engineer for East Suffolk IDB, part of the Water Management Alliance (WMA), Eastern Drainage Boards.

To request a quote or find out more contact us on 01444 401 840 or email