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Braemar floodplain restoration, River Dee

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Catchment Information

The Dee catchment lies in NE Scotland. The catchment area of the Dee is around 2105km2. The source of the River Dee is the Wells of Dee, a spring high on the slopes of Braeriach in the Cairngorm Mountains. It is 137 km in length and flows from the Cairngorms, through the rolling hills to the largely arable plains before discharging into the sea at Aberdeen. The river is renowned for Salmon fishing and this pursuit contributes significant income to the local economy. The Dee is a designated SAC for Atlantic salmon, freshwater pearl mussels and otter. 

The River Dee has a history of flood rich and flood poor periods interspersed by large flood events.  The greatest recorded historical flood event was the ‘Muckle Spate’, of August 1829.  It destroyed the bridge at Ballater and inundated settlements and large areas of the floodplain.  The December 2015 Storm Frank flood was of a similar magnitude and resulted in extensive damage to property and infrastructure along the whole Dee valley.

The floodplain restoration site, upstream of the village of Braemar lies on the main channel of the River Dee, and has a catchment area of 370km2.  The bedrock geology of this sub-catchment is dominated by Cambro-Ordivician granites and Moinian metamorphic rocks.  These rocks are overlain by fluvio-glacial deposits, glacial till and alluvium.  The mean annual precipitation is approximately 1400 mm. 

Stage of project

Work completed

Monitoring Undertaken

Yes

Modelling Undertaken

Yes

Project Descriptions

 In 1937, a 100+ year recurrence interval flood eroded a ~60 m long section of the 18th Century levee (flood embankment) on the Allanmore floodplain west of Braemar.  This resulted in the cutting of a new channel (avulsion) in the floodplain and deposition of gravel .  To reduce future inundation of rough grazing land on the floodplain, the estate plugged the gap with a substantial new levee (~60 m long by 5 m wide) in 1984.  The levee was built up with concrete and stone rubble, earth, several cars and the river side of the embankment was faced with railway sleepers and corrugated metal.  In effect the ’new’ channel became  sealed off and since the embankment was constructed has functioned as a backwater fed by groundwater, overtopping flows from the Dee and localised surface runoff.

Under the current Dee catchment management plan and with funding from the EU ‘Pearls in Peril’ project, the car barrier was removed in October 2015 to re-connect the river with its floodplain and the backwater. The work was carried out by numerous partners co-ordinated through the Dee Catchment Partnership.  

The potential benefits of reconnecting the backwater and floodplain area (~0.67 km2) on the north bank are: 1. Increased floodwater storage and thus decreased flood risk downstream; 2. Improved riparian habitat diversity; 3. Increased habitat area and diversity if the incipient channel continues to migrate across the floodplain; 4. Demonstration of this style of habitat restoration technique that could inform similar remedial action in other river systems. 5. Increased amenity value. 

Pre- and post-removal monitoring has taken place since June 2013 and is ongoing.  Monitoring includes water level recording in the reconnected backwater and floodplain, vegetation surveys, pebble counts, topographic surveys and time lapse photography with automated cameras.

Partners

SEPA

SNH

Cairngorms National Park Authority

Aberdeenshire Council

Dee Catchment Partnership

Mar Lodge Estate (NTS)

Invercauld Estate

Mar Estate