River Tweed and it's Drainage basin

How long is the River Tweed?

97 Miles (156 kilometers)

Where is the source?

Tweedsmuir Hills in the southern Scottish Uplands

Where is the mouth?

Berwick upon Tweed into the North Sea

How large is the river catchment area?

approximately 5000 km^2

Precipitation at the river Tweed

- High rainfall totals in upland areas due to relief and rainfall (1,000-2,000 mm/year)

- Higher in winter, lower in summer

- Snowfall in extreme upland areas contributes to spring snowmelt, affecting discharge

Soil and Geology at the River Tweed

- Impermeable bedrock in some upland areas (silurian and ordovician rock) increases surface runoff

- Peaty soils in upland areas store water but become saturated quickly, causing surface runoff to increase

- Sandy soils in lowland areas have some infiltration and percolation, but no particularly high levels of this.

Vegetation and Land cover at the river tweed

- Forest cover (20% of drainage basin) in upper basin enhances the interception, increases evapotranspiration and reduces surface runoff

- Grassland and farmland dominate lower basin which have less interception than the forested areas

- Ploughed fields can increase surface runoff

- Moorlands in uplands (Lammermuir hills) have thin solid and low infiltration which causes high surface runoff

Human activity/ land use at the river tweed

- Sheep grazing and arabke farming cause compaction of soils, which reduces infiltration

- Use of drainage ditches in agricultural fields cause runoff to flow into rivers quickly

- Urbanisation (Peebles, Berwick) creates more impermeable surfaces which causes a larger surface runoff and a reduced lag time

- Afforestation is undertaken in some areas to reduce flood risk

- Megget and Talla reservoirs in the upper basin regulate discharge, store water and alter the natural flow regime, reducing the peak river flow during storms and other weather events.

River Regime at the river tweed

- Simple regime with fairly predictable patterns

- High river flow in winter, lower in summer

- Influences by seasonal precipitation, temperature variation, snowmelt and reservoir management

Storm hydrograph at the river tweed

- Steep hydrographs at the upland areas due to steep slopes, impermeable geology and thin soils

- Flashy hydrographs after intense rainfall or snowmelt

- Longer lagtime in lowland areas due to flatter land and permeable soils

Management strategies undertaken at the river tweed

- Soft engineering eg floodplain zoning, riverbank planting and afforestation in the local area

- Flood warning systems have been established in towns like Peebles and Kelso

- River tweed catchment partnership promotes sustainable land and water management eg wetland restoration and reducing agricultural runoff

Impacts of climate change on the river tweed

- Increased rainfall intensity may lead to flash flooding

- Warmer winters lead to less snow, more rain, changing the spring flow

- Longer dry periods in summer lead to increased water stress and reduced base flow

- Potential for increased soil erosion and sedimentation due to intense rainfall

River tweed as a system

- Inputs - high precipitation

- Storage - Interception (moderate in forested areas), soil moisture, groundwater (in permeable areas)

- Flows - Surface runoff, throughflow, groundwater flow

- Outputs - River discharge into the North sea, Evapotranspiration.