Drainage Basins Flashcards
Inputs in the drainage basin
Precipitation - mostly rain but also included snow, hail, dew and frost
Storage in the drainage basin
Interception - water lands on vegetation or other structures before reaching soil. Only temp
Vegetation storage - taken up by plants
Surface storage - includes ponds puddles and lakes
Soil storage
Groundwater storage
Channel storage
Flows in the drainage basin
Infiltration - water soaks into soil
Overland flow
Through fall - water dripping from one leaf to another
Stem flow
Through flow - water slowly moves downhill through the soil
Percolation - water seeps through soil down to water table
Groundwater flow - water slowly below water table through permeable rock
Base flow- groundwater flow feeds into rivers through river banks
Interflow - water flow downhill through permeable rock above water table
Channel flow - water flowing in river
Outputs in the drainage basin
Evaporation
Transpiration
Evapotranspiration ( potential and actual)
River discharge
The water balance
Water balance is worked out from inputs and outputs and affects how much water is stored in the basin. The general water balance in rhe UK shows a seasonal pattern.
In wet seasons, precipitation exceeds evapotranspiration creating water surplus. The groundwater stores fill with water so there’s more surface run off as if is fully saturated and there is high discharge and river levels rise
In drier seasons precipitation is lower than evapotranspiration. Ground water stores are depleted as some water is used and some flows to river channel but isn’t replaced by precipitation. At the end of a dry season there is a deficit of water in the ground. The ground stores are recharged in the next wet season
Where is the Eden basin located
North - West England
Flows through Cumbria
Between mountains of the Lake District and the Pennies
Largely rural although it does flow through the city of Carlisle
How do the characteristics of River Eden Basin affect the water cycle
Rainfall is higher than the national average in the Eden Basin because of the mountains encouraging orographic rainfall. This means lots of water enters the river channel
Eden basin is long and narrow which increases lag time
The slopes in the basin are steep which reduces lag time and increases peak discharge
Made up of both igneous rock (impermeable) and limestone and sandstone (permeable)
Land use changes in the Eden basin has increased flood risk - FARMING
More intense farming has caused soils to become compacted eg by heavy machinery or trampling by livestock. Between 2000 and 2009 there was a 30% increase in the number of cattle in the Eden valley meaning more land likely to be trampled. This reduces infiltration so surface run off is higher. This means water levels rise quickly during heavy rainfall increasing flood risk. Grazing also reduces vegetation that can intercept rainfall resulting in more water reaching river.
Land use changes in the Eden basin have increased flood risk - CONSTRUCTION
Although majority of the Eden basin is rural, built up areas have increased. Many new housing estates have been built in and around Carlisle in recent years eg the Eden Gate development including garden village and up to 1000 homes. Surfaces here tend to be impermeable which reduces infiltration and increases run off.
Some developments particularly near Carlisle have been built on floodplains which has created flood risk and has required construction of flood defences to protect homes. Building here can cause flooding downstream as water would naturally infiltrate on the floodplain flows downstream instead
Land use change in the Eden basin has caused flooding - DEFORESTATION
Much of the original forest cover in the Eden basin has now been removed, giving way to large areas of open grassland. Trees increase infiltration and decrease runoff so fewer trees means more runoff, flashier hydrographs and more flood risk
Storm Desmond causing severe floods in the Eden Basin
December 2015
Devastating floods in Cumbria some of the worst in the Eden Basin
Record rainfall in some areas - Shap a village in the Eden Basin 262.6mm of rain fell in. 48 hours
Carsile was badly affected with more than 2000 properties flooded
