1.3 water budgets and river systems

What is a water budget

• annual balance between precipitation, evapotranspiration and runoff (BALANCE BETWEEN OUTPUTS & INPUTS)

• Helps understand when water enters and leaves drainage basin

What is positive and negative water balance in a water budget

• Positive water balance- wet season, precipitation is higher than evapotranspiration creating water surplus, soil fills with water increasing surface runoff, river levels.

• Negative water balance- dry season, evapotranspiration is higher than precipitation creating water deficit.

Soil moisture in the hydrological cycle

• Field capacity is max amount soil can hold. Its reduced during water deficit (evapotranspiration exceeds precipitation)

• Water surplus is soil becoming oversaturated, causing runoff.

• Flash floods occur during heavy rainfall after drought when soils cant absorb water quick enough.

Rainfall effectiveness and water availability in seasons

• In summer, evapotranspiration is higher than precipitation- water levels low in rivers and soil moisture decreases.

• Uk water year is in October where precipitation exceeds evapotranspiration.

What is a river regime and what is it influenced by

• annual variation in discharge (flow) of a river in a specific point.

• levels of discharge are influenced by drainage basin area- larger basin collect more water causing higher discharge.

• temperature- low river flow caused by cold temp- rivers freezing or hot causing evaporation.

• max altitude- rivers from high alt have steeper gradient causing faster flow.

• geology- hard rock slows erosion causing stable flow, soft rock erodes causing variable flow

• mean annual precipitation

What is a simple and complex river regime

• Simple- river has clear period of high then low discharge

• Complex- multiple rivers cross several climate zones so have multiple periods of high and low discharge.

Amazon as a water regime

• High river flow in dec-may and low in June- Nov.

• There’s moderated variability in river flow in seasons

• Human influence increasing through urbanisation/ deforestation which would increase the variability in river flow.

What is a storm hydrograph

• shows changes in a rivers discharge before and after a storm/ rainfall

• theres a flashy or a flat hydrograph

Describe features of a flashy hydrograph

• has high peak discharge (volume of water running through river)

• steep rising limb (how discharge over river is increasing)

• short lag time (time delay between peak rainfall and peak discharge)

This hydrograph appears after a storm

Describe features of a flat hydrograph

• low peak discharge (less water running through river)

• gentler rising limb

• long lag time (takes long between peak rainfall and peak discharge)

This hydrograph appears in a drainage basin with less water

Weather/ climate affecting a flashy and flat hydrograph

• Flashy- intense storms, heavy rainfall exceeds soil capacity causing runoff, low evaporation rates

• Flat- steady rainfall, slow snowmelt dosen’t exceed soil capacity, high evaporation rates

Rocks/soil/relief affecting a flashy and flat hydrograph

• Flashy- impermeable rock not allowing water through, clay soils have low infiltration rates, steep slopes

• Flat- permeable rocks, sandy soils have high infiltration rate and gentler slopes

Drainage basin characteristic affecting flashy and flat hydrograph

• Flashy- small basin, circular shape, more streams flowing to main river.

• Flat- large basin, elongated shape, few streams into main river.

Vegetation affecting a flashy and flat hydrograph

• Flashy- minimal veg causing low interception and infiltration

• Flat- lots of veg causing high interception

Antecedent (pre existing) conditions affecting flashy and flat hydrograph

• Flashy- basin already wet from previous storm, soil is saturated

• Flat- dry basin, low water table (enough capacity to store more water)

Human activity affecting flashy and flat hydrograph

• Flashy- deforestation reducing interception, urbanisation increasing permeable surfaces,

• Flat- rural areas, reforestation