EQ1: What are the processes operating within the hydrological cycle from global to local scale?

Question 1

What are systems, and the 2 different types of systems?

Answer 1

SYSTEM
- Any set of interrelated components that are connected together to form a working whole, characterised by inputs, stores, processes (flows) and outputs, there are two types:

1. OPEN SYSTEM
   - Receives inputs from and transfers outputs of energy and matter to other systems.
2. CLOSED SYSTEM
   - Occurs when there is a transfer of energy but not matter between the system and its surroundings (the inputs come from within the system).

Question 2

What is the Global Hydrological Cycle, and what type of system is it?

Answer 2

GLOBAL HYDROLOGICAL CYCLE

1. This cycle is a closed system because all the water is continually circulating through the stores and there is a constant and finite volume of water in the system - no external inputs or outputs.
   a) Fixed volume - 1,385 million km3.
2. It can exist as different states (liquid, vapour, solid) with varying proportions as a result of both physical and human reasons.

Question 3

What drives the Global Hydrological Cycle?

Answer 3

POWERED BY SOLAR ENERGY AND GPE

1. This global circulation of water is driven by solar energy; heated by solar energy (from the Sun heating the water on Earth’s surfaces evaporating into the atmosphere and evapotranspiration. Humid air rises, cools condenses to form clouds).
   a) This water is then returned back to land and oceans as gravitational potential energy is converted to kinetic energy as the water moves through the system, taking a variety of time periods.

SOLAR ENERGY

• Energy from the sun, heating water and causing evaporation and transpiration.
• More evaporation occurs as the global climate warms, which increases moisture levels in the atmosphere, increased condensation as the air cools and therefore greater precipitation.

GRAVITATIONAL POTENTIAL ENERGY
- Ways in which water accelerates under gravity, thus transporting it to rivers and eventually to the sea. Keeps the water moving in a sequence of inputs, outputs, stores and flows.

Question 4

What are the different systems approaches in the Hydrological Cycle?

Answer 4

SYSTEM APPROACHES

1. Stores (Stocks)
   - Reservoirs where water is held (oceans, ice (Cryosphere), rivers, lakes). Stored as either Blue Water or Green Water.
2. Fluxes (Flows)
   - Measurement of the rate of flow between the stores.
3. Processes
   - The physical mechanisms (such as evaporation) that drive the fluxes of water between the stores.

BLUE WATER
- Water that is stored in rivers, streams, lakes and groundwater in liquid forms v (visible part of the hydrological cycle).

GREEN WATER
- Water stored in the soil and vegetation (the invisible part of the hydrological cycle).

CYROSPHERE
- Areas of the Earth where water is frozen into snow or ice.

Question 5

How much of the Earth’s water is freshwater and accessible?

Answer 5

EARTHS FRESHWATER

1. Only 2.5% of Earth’s water is fresh water (not saline) - the amount needed for life to survive.
   a) Majority of freshwater is inaccessible as it is stored in glaciers/ice (68.7%) caps or even groundwater (30.1%) which is deep and hard to access with limited technology.
   - Not all surface water is accessible, such as permafrost.
   b) The primary source for accessible water is found in rivers, which constitutes only 0.007% of total water, which threats and concerns around water security.

25% of global water is freshwater (not saline)
69% of this is locked in cryosphere - largely inaccessible
30% of this is deep groundwater
1% of freshwater is accessible
0.03% of the global total is accessible

Question 6

What are the different water stores and their relative importance?

Answer 6

STORES

1. Oceans
   a) 96.9% of total water.
   b) 0% of freshwater.
   c) 1,335,040 Volume (1000㎦).
   d) 3,600 Years Residence time.
2. Cryosphere
   a) 1.9% of total water.
   b) 68.7% of freshwater.
   c) 26,350 Volume (1000㎦).
   d) 15,000 Years Residence time.
3. Terrestrial
   - Groundwater.
   - Surface (Rivers).
   - Soil Moisture.
   - Biosphere.
   a) 1.1201% of total water.
   - 1.1%
   - 0.01%
   - 0.01%
   - 0.001%
   b) 31.35% of freshwater.
   c) 15,600 Volume (1000㎦).
   d) N/A Years Residence time.
   - 100 to 10,000 years for fossil water.
   - 2 weeks to 10/50 years (rivers).
   - 2 to 50 weeks.
   - 1 week.
4. Atmospheric
   a) 0.01% of total water.
   b) 0.04 of freshwater.
   c) 13 Volume (1000㎦).
   d) 10 days Residence time.

Question 7

What are the annual fluxes of water stores?

Answer 7

ANNUAL FLUXES IN 1000㎦

1. Ocean to Atmosphere = 413
2. Atmosphere to Ocean = 373
3. Atmosphere to Land = 113
4. Land to Atmosphere = 73
5. Transfer in Atmosphere = 40
6. Land to Oceans = 30

Question 8

What is the global water budget?

Answer 8

GLOBAL WATER BUDGET

• The annual balance of water fluxes (flows) and the size of the water stores.
• Constant circulation at different speeds means generally water is globally considered as a renewable resource although an imbalance across countries is adding pressure to this cycle.

Question 9

What is residence time?

Answer 9

RESIDENCE TIME

- The average time a water molecule will spend in a reservoir or store.

Question 10

What are the Non-renewable stores of Water?

Answer 10

NON-RENEWABLE STORES OF WATER

1. FOSSIL WATER
   - Ancient, deep groundwater from former pluvial (wetter) periods, that have been contained in an undisturbed space, usual groundwater in an aquifer.
   - Stored for over 10,000 years yet new technologies now make it possible to access water stores - allowing it to be extracted, yet it is not renewable nor replenished.
   - Used in Algerian potato farms.
2. CYROSPHERE LOSS
   - In the Cryosphere, seasonal thaws bring increased surface saturation and thinning permafrost. If this thaw becomes continuous, water flows away and is lost.
   - There are freeze/thaw seasonal differences with winter snow insulating the snow and reflecting 85% of solar radiation which maintains the permafrost.
   - However, spring thaw causes rapid runoff and the summer thaw produces surface runoff, increasing evaporation tenfold.
   - This freeze-thaw cycle causes the seasonal release of biogenic gases (caused by plant decomposition) into the atmosphere, as well as carbon and nutrients into rivers and seas.

Question 11

What is the key terminology in a river basin?

Answer 11

DRAINAGE BASIN - A ‘Catchment area’ that is drained by a river and its tributaries and separated by neighbouring drainage basins by a ridge of higher land known as the watershed. It’s an open system so it’s linked to other systems by inputs and outputs and involves linked processes and stores.

PRECIPITATION - Any form of water (Liquid or Solid) that falls from the sky, has four main types; rain, sleet, snow and hail. It is a significant input into any drainage basin system and varies over type and intensity over time and space.

WATERSHED BOUNDARY - A high point of land or ridge (usually mountains and hills) that divides two drainage basins. This defines the boundary of a drainage basin.

SOURCE - The start of the river, usually a spring (furthest point of the river away from the mouth).

HEADWATERS - A tributary stream of a river close to or forming part of its source.

WETLANDS - Land consisting of marshes or swamps; saturated land.

TRIBUTARY - A river or stream flowing into a larger river or lake.

CONFLUENCE - The point at which two rivers meet.

BANKSIDE - The edge of a river; the area of land immediately adjacent to a river.

WATER TABLE - Also called the Ground Water table, it is the upper level of permanently saturated soil and rocks/zone of saturation (the zone where all pores in rocks and soils are full of water). Porous rocks that hold water are aquifers.

GROUNDWATER - Water held underground in the soil or pores and crevices in the rock.

STREAM CHANNEL - The river between river banks.

Question 12

What is precipitation and what conditions are needed for it to form?

Answer 12

PRECIPITATION

1. Four main types of precipitation: Rain, Snow, Hail and Sleet.
2. The conditions needed are:
   a) Air cooled to saturation point with a relative humidity of 100%.
   b) Condensation nuclei.
   c) A temperature below Dew Point.

CONDENSATION NUCLEI - Such as dust particles, to facilitate the growth of droplets in clouds, as water condenses from vapour to a liquid/droplets.

DEW POINT - The atmospheric temperature (varying with pressure and humidity at which water droplets can condense and dew forms, it is a measure of atmospheric moisture.

RAIN SHADOW - A dry area on the leeward (downwind) side of the mountain. It receives little rainfall as the mountains shelter it. As moist air is forced to rise on the windward side of the mountain, rainfall occurs due to ADIABATIC COOLING (When the volume of air increases but there is no addition of heat and condensation to dew point). The air, lacking in water, is then drawn and is adiabatically warmed by compression. This leads to an arid ‘shadow’ area.

Question 13

What are the 3 different types of rainfall?

Answer 13

TYPES OF RAINFALL
1. Orographic - When air is forced to rise over a barrier, such as a mountain, it cools and condensation occurs forming rain. The leeward (downwind) slope receives relatively little rain, which is known as the rain shadow effect. Its concentrated on the windward slopes and summits of mountains. The West of the UK receives the highest rainfall due to warmer moist Atlantic Air rises over the uplands.

2. Frontal (Cyclonic)- This happens when warm air which is lighter and less dense, is forced to rise over cold, dense air. As it rises, the air cools and its ability to hold water vapour decreases. Condensation occurs and clouds (mainly Cumulus clouds) and rain form.
3. Convectional - Occurs when the land becomes hot, the air above it becomes warmer, expands and rises. As it rises, the air cools and its ability to hold water vapour decreases. Condensation occurs and clouds develop. If the air continues to rise and move from an area of high pressure into an area of low pressure, the rain will fall. This type of rainfall is common in tropical areas and the UK during the Summer.

Question 14

How do inputs affect the drainage basin cycle?

Answer 14

INPUTS (PRECIPITATION)

• The input of water into the drainage basin system. It includes all forms of moisture entering: Hail, Snow, Dew, Frost, Sleet and Rain.
• Precipitation input on the Drainage Basin Depends on:
  1. Amount of Precipitation
• It can have a direct impact on drainage discharge, the higher the amount the less variability in its pattern.

2. Type of Precipitation
   - The formation of snow can act as a temporary store and large fluxes of water can be released after a period of rapid melting resulting from a thaw.
3. Seasonality
   - Strong seasonal patterns of rainfall or snowfall will have a significant impact on the physical processes operating in the drainage basin system.
4. Intensity of Precipitation
   - Significant impact on flows on or below the surface. It is difficult for rainfall to infiltrate if it is very intense, as the soil capacity is exceeded.
5. Distribution of Precipitation within a Basin
   - Particularly noticeable in vast basins, where tributaries start in different climate zones.
6. Variability
   - Secular variability happens long term i.e as a result of climate change trends.
   - Periodic variability happens in an annual, seasonal, monthly context.
   - Stochastic variability results from random factors, for example in the localisation of a thunderstorm within a basin.

Question 15

What are the different stores in the drainage basin cycle?

Answer 15

STORES

1. Interception
   - The temporary storage of water when it lands on vegetation or structure like buildings before it reaches the soil.
2. Vegetation Storage
   - Any moisture is taken up by vegetation and held within plants. Plants and trees take up water through their roots and water are stored here. Dry leaves and stems have the greatest water storage capacity.
3. Surface Storage
   - The storage of water on the surface including puddles, ponds and lakes.
4. Soil water/Moisture Store
   - The storage of water in the soil. Water is held in the small gaps between soil particles.
5. Groundwater Store
   - The storage of water in the ground rocks of permeable rock. The water is held in {Pervious} cracks (limestone) and bedding planes (sedimentary rock) or {Porous} pores (chalk). Rocks with lots of water storage are called aquifers.
6. Channel Store
   - The storage of water in the river channel. As water is being transported to the sea is a store of water.

Question 16

What are the different flows in the drainage basin cycle?

Answer 16

FLUXES/FLOWS/PROCESSES/TRANSFERS

1. Interception Loss
   - Water that is retained by plant surfaces and later evaporated or lost by the vegetation and transpired. Can be lost when:
   a) The rain is intense (heavy) or a long duration of time (relentless) instead of light rain (drizzle) over a short duration of time (periodic).
   b) Vegetation cover varies considerably with the type of tree, with dense needles of coniferous forests allowing greater accumulation of water and increased interception storage. Yet there are contrasts between sparser deciduous forests seasonally (winter/summer loss of leaves).
   c) The strength of the wind can also influence this, with strong winds resulting in a lower interception storage.
2. Throughfall
   - Also known as inter-flow, it’s the downward flow of water moving downwards from interception storage to the surface, seeping laterally through soil below the surface, but above the water table.
3. Stem Flow
   - Water flowing down plant stems or drain pipes.
4. Surface Runoff
   - The horizontal flow of water over the surface of the land either in little channels or over the whole surface.
   - Saturated overland flow occurs when water accumulates in the soil until the water table reaches depression storage capacity, forcing further rainwater to run off the surface. It’s familiar with thin soils of moderate permeability. Areas near riverbanks often have high moisture levels and may produce a saturated overland flow.
   - Infiltration-excess overland flow occurs when rainfall intensity exceeds the infiltration capacity, so the excess water flows over the ground surface.
   a) Precipitation intensity must exceed the infiltration rate.
   b) Depression Storage capacity in puddles has been exceeded.
   c) The rapid melting of snow, or frozen surface, reducing soil infiltration.
   d) Soil type such as impermeable clay which reduces.
   e) ‘Baked’ unvegetated surfaces, such as in arid or semi-arid regions, as this type of ground, has minimal infiltration capacity - it can lead to soil erosion as sediment is removed.
5. Infiltration
   - The gradual movement of water entering the topsoil, this is most common during slow or steady rainfall. Infiltration is inversely related to surface runoff. The Infiltration capacity is the maximum rate at which the soil can absorb precipitation in a given condition (mm/hr) The rate of infiltration depends on:
   a) Infiltration capacity decreases with time through a period of rainfall.
   b) The degree of saturation, also known as antecedent conditions/soil moisture, (amount of water already in the soil) within the soil as the Infiltration-excess overland flow will take place if the soil is saturated.
   c) Soil Texture (sand, silt, clay…) influences soil porosity with sand having a higher infiltration capacity. Less permeable clays lead to flooded land.
   d) Amount of seasonal changes in vegetation cover is a crucial factor, with infiltration more significant in land covered by forests/moorland, which has led to campaigns to vegetate upland catchments that flow into areas liable to flooding.
   e) Nature of soil surface and structure. Compacted (grazing fields contains a compacted soil density) surfaces inhibit infiltration.
   f) Soil depth, with shallow soils reaching infiltration capacity faster.
   g) Slope angle/gradient can also be significant, with steeper slopes tend to encourage overland runoff, with shallower slopes promoting infiltration.
6. Soil Throughflow
   - (Inter-flow), The horizontal/lateral flow of water through soil below the surface but above the water table towards the river through natural pipes and percolines (lines of concentrated water flow between soil horizons to the river channel).
7. Percolation
   - The downward seepage of water from the soil into the soil under gravity, especially on permeable rocks - filling the water table up.
   a) Deep transfer of water into permeable rocks either Pervious (has joints) or Porous.
8. Groundwater (Base) Flow
   - The horizontal slow movement of water through the rocks (cracks/bedding planes/pores) towards the river channel. This is the movement of water below the water table sideways to the river. It is a vital regulatory component of maintaining a steady level of channel flow in varying weather conditions.
9. Channel Flow
   - Takes place once water from three transfer processes (overland flow, throughflow or groundwater flow) reaches into a rivulet, stream or river. Direct channel precipitation is added to the channel store. The discharge of the river is the volume of water passing a specific gauging station per unit of time and is measured in cubic meters per second (cumecs).

Question 17

What are the different outputs in the drainage basin cycle?

Answer 17

OUTPUTS -
1. Evaporation - The output of water when water is heated and converted into vapour.

2. Transpiration - The biological output of water where moisture is taken into plants through their roots, moved to the leaves by capillary action and then transpired onto the leaves stomata (pores).
3. Evapotranspiration - The combined output of water from evaporation and transpiration. The total amount of moisture removed from a drainage basin. Can be understood through potential evapotranspiration and actual evapotranspiration.
4. River Channel Flow Out to Basin’s Exit - The output of water from a river channel out to sea.

Question 18

What are the different types of transpiration?

Answer 18

POTENTIAL EVAPOTRANSPIRATION (PEVT)
- The amount of water that could be lost by evapotranspiration if there were sufficient moisture provisions for use by vegetation.

ACTUAL TRANSPIRATION (EVT) 
- The combined amount of water is lost through transpiration and evaporation to the atmosphere.

Question 19

What is the impact of physical factors on the drainage basin?

Answer 19

PHYSICAL FACTORS IMPACT
1. Climate
a) The temperature will alter the rate of evapotranspiration
Impacts the amount of precipitation input and evapotranspiration output.
b) Precipitation with a heavy intensity over a long duration of time can increase input and saturated soils, while light rain, periodically is opposite.
c) Rapid thawing/melting of snow/ice can increase drainage discharge, delayed flow.
d) Has an impact on the vegetation type.
e) Hours of sunshine will increase evaporation.
f) Wind Speed can decrease interception loss as intercepted rain is dislodged. It can also increase evaporation rates, by reducing relative humidity.

2. Soils
   a) Antecedent conditions, amount of water already in the soil.
   b) Soil texture can influence soil porosity with soil having an infiltration capacity of 3-12mm/hr with less permeable clays 0.4mm/hr.
   c) Seasonal changes in vegetation cover, infiltration more prominent in forests (50mm/hr) hence the recent drive to vegetate upland catchments that are liable to flooding. Permanent pasture has infiltration rates of 13-23 mm/hr.
   d) Nature of soil surface and structure, compacted surfaces inhibit infiltration 10mm/hr. Vegetation alters soil formation.
   e) Soil depth with thin soils reaching infiltration capacity faster. Deep soils increase soil capacity.
3. Vegetation
   a) Dense needles of coniferous forests allowing greater accumulation of water and increased interception storage.
   b) Sparser deciduous forests seasonally contrast with the loss of leaves in winter.
   c) Arable crops have a low interception rate.
   d) As more tree canopies become saturated, so more excess water will reach the ground.
4. Geology
   a) Can impact subsurface processes, such as percolation and groundwater flow, permeable rocks allow more percolation which can provide greater recharge of groundwater.
   b) Indirectly alters soil formation.
   c) Large, circular drainage basins collect more precipitation, as well as more tributaries increasing the discharge.
   d) Higher drainage density encourages fast movement across the basin.
   e) Can determine how high the water tables are.
   f) {Pervious} cracks (limestone) and bedding planes (sedimentary rock) or {Porous} pores (chalk). Rocks with lots of water storage are called aquifers.
5. Relief
   a) Slope angles can be very significant with steep slopes promote faster movement and shorter storage times than gentle slopes.
6. Water (Evaporation)
   a) Size of the water body.
   b) Depth of water.
   c) Water quality (impurities will increase evaporation point).
   d) Vegetation cover.
   e) Colour of the surface (Albedo - A measure of the proportion of incoming solar radiation that is reflected by the surface back into the atmosphere). Low albedo will absorb more solar radiation, increasing evaporation.

Question 20

How can humans impact on the inputs of the drainage basin cycle?

Answer 20

HUMAN IMPACTS ON INPUTS

1. Cloud Seeding
   - Attempt to change the amount or type of precipitation by dispersing substances (Silver Iodide pellets or Ammonium Nitrate) into the air that serve as cloud condensation nuclei.
   - Becoming more dependable and affordable water-supply practice, in China they used it to clear the air of pollution.

Question 21

How can humans impact on the Stores/Flows of the drainage basin cycle?

Answer 21

HUMAN IMPACT ON STORES/FLOWS

1. Arable (Crops) and Pastoral (Animal) Farming
   - Animals compacting soils as well as consuming vegetation through grazing, which reduces infiltration. Meanwhile farming down contours/furrows can increases surface runoff. Yet Ploughing can increase infiltration by loosening and aerating the soil.
2. Groundwater Over Abstraction
   - Some places the groundwater is abstracted from aquifers faster than it is being replaced, causing reduced groundwater flow and a lower water table. With many abstracting for irrigation and drinking water.
   - The Aral Sea is shrinking due to Soviet irrigation schemes in the 1960s. By 1994 volume had reduced by 75%.
3. Industrial decline
   - Increased groundwater storage, increasing the risk of groundwater flooding if the water table reaches the land surface.
4. Changing land use (Urbanisation)
   - Creates impermeable surfaces that reduce infiltration and increase surface runoff. Can also increase throughflow through artificial drains - increasing river discharge
   - Impermeable areas allow only 5% deep infiltration (compared to 25% in natural areas), 55% runoff (compared to 10% in natural areas).
5. Deforestation - Leads to a reduction in evapotranspiration and an increase in surface runoff. Increasing flooding potential leads to a decline of surface storage and a decrease in the lag time between peak rainfall and peak discharge, as well as increasing sediment load downstream. Accelerating the natural processes.

Question 22

How can humans impact on the Outputs of the drainage basin cycle?

Answer 22

HUMAN IMPACT ON OUTPUTS

1. Dam/Reservoir Construction
   - Dams increase water stores and evaporation and reduce downstream river discharge, potentially leading to loss of vegetation downstream.
   - 7% more water is evaporated from the world’s reservoirs than is used by people. Salinity levels within the reservoir can also rise as its water evaporates.

Question 23

How has deforestation in a named location impacted the local drainage basin cycle?

Answer 23

AMAZONIA CASE STUDY
1. Deforestation of 20% of the entire forest, at an accelerating rate, through cattle ranching, large-scale commercial agriculture for biofuels…

2. Amazon contains 60% of the World’s rainforests, trees acting as ‘green lungs’ by removing CO₂ as they photosynthesise acting as carbon sinks. Slash and Burn farming releases this Carbon back into the atmosphere.
3. The enormous impact of water cycling as it is an example of a self-sustaining cycle where water is effectively recycled within the system, with 75% of intercepted water returned by EVT to the atmosphere, but only 25% returned when the forest is cleared. The drier climate can lead to desiccation and further rainforest degradation.
   a) A vulnerable area due to El Nino and the occurrence of droughts.
4. The sheer scale can have a very significant impact on the water cycle, as more water runs off into the Amazon drainage system, increasing possibilities of severe flooding and mudslides, but also aquifer depletion, as less water infiltrates to recharge them.
   a) Overland flow will increase soil erosion and degradation as nutrients are washed away.

Question 24

What is the water budget and how do you calculate it?

Answer 24

WATER BUDGET

• The natural annual balance between inputs (precipitation) and outputs (evapotranspiration and channel flow) in a given river area (Whatever falls as precipitation should be balanced out by other components).
  1. The formula is:
  a) P = Q + E +/- store change.
  b) Precipitation (P) = Channel discharge (Q) + Evapotranspiration (E) +/- Change in soil moisture or groundwater store.
  c) Can identify where:
• P>ET = Positive Balance (Flood) - Jan / Nov.
• P

Question 25

What is the various terminology associated with a water budget diagram?

Answer 25

WATER BUDGET
1. Soil Moisture Surplus - Precipitation is greater than potential evapotranspiration and the soil water store is full, so there is a surplus/excess of soil moisture for plant use, runoff into streams and recharging groundwater supplies.

2. Soil Moisture Utilisation - Potential evapotranspiration increases and exceeds precipitation, so there is more water evaporating from the ground surface and being transpired by plants than is falling as rain. Water is also drawn up from the soil by capillary action. The water is gradually used up faster than it is replenished.
3. Maximum Annual Temperatures - High temperatures cause maximum evapotranspiration, precipitation is at a minimum and therefore plants use up the soil moisture store. River levels will fall and crops will need irrigation.
4. Soil Moisture Deficit/Defiancy - The soil water store has been used up by high rates of evapotranspiration and low precipitation. Rivers run dry and drought ensues. Plants can only survive if they are adapted to periods of drought or are irrigated.
5. Soil Moisture Recharge - Occurs when moisture from precipitation infiltrates and percolates in the stores to repay the soil moisture utilisation/deficit.
6. Field Capacity - The normal amount of water that can be held in the soil. At this point, the soil is full of water and cannot hold any more.
7. Potential Evapotranspiration - An estimate of the amount of water that could be lost by evapotranspiration, in a given period, if there was sufficient moisture available (depending on temperature and air humidity).
8. Actual Evapotranspiration - The amount of water that is lost through transpiration (release from leaves) and evaporation (heating of water on surfaces) to the atmosphere.

Question 26

How are water budgets influenced by climates?

Answer 26

WATER BUDGETS AFFECTED BY CLIMATE

1. Water Budgets vary with climate type and acts as a useful indication of available water supplies.
   a) Places of higher latitude being more familiar with precipitation in the form of snow or sleet, which is stored in the colder months (Winter/Spring) due to the colder temperatures. This store is then released as meltwater under a warmer climate (Summer).
   b) Temperate locations will see more consistent precipitation, yet temperatures are seasonal, with summer seeing soil moisture utilisation and deficit.
   c) Places closer to the equator will expect warmer climates throughout the year as well as lower rates of precipitation (other than the rainforested areas), this means that for the majority of the year there is soil moisture deficit.
   - Flash flooding is common in drylands, where sun-baked soils cannot absorb intense storm rains fast enough. The surface soil becomes saturated, causing rapid surface runoff.
2. Barrow, Alaska (Polar Example)
3. Cairo, Eygpt (Tropical Example)

Question 27

What is a river regime and the 2 different types?

Answer 27

RIVER REGIMES
- Indicates the annual variation in the discharge of a river at a particular point/gauging station and is measured in cumecs. Much of this river flow is not from immediate precipitation or run-off but supplied from groundwater between periods of rain, which feeds steadily into the river system from base water flow. This is influenced by climate, geology, soils and human activity (land-use changes).

1. Simple Regime
   a) Rivers experience a period of seasonally high discharge, followed by a low discharge.
   b) Often rivers when inputs depend on glacial meltwater, snowmelt or seasonally storms.
   c) Rivers within temperate climates, which rise in mountainous regions where summer snowmelt occurs tends to be like this.
2. Complex Regime
   a) Larger rivers cross several different relief and climate zones and therefore experience the effects of different seasonal climatic events.
   b) True of rivers such as the Mississippi (covers 40% of the continental United States) or the Ganges influenced by numerous tributaries from different altitudes/climates.
   c) Influences diminish extreme discharges and increase the regularity of the mean monthly discharge from upstream to downstream.
   d) Human factors also contribute to their complexity, such as damming a river for energy or irrigation.

Question 28

What factors affect River Regimes?

Answer 28

RIVER REGIME INFLUENCES

1. Climate Zones
   a) The longer the river, the more complex its variables tend to be.
   b) As the river may cross several climatic zones and encounter very different land uses and population densities along their length.
   c) Mountain climate zones have a high river flow in Spring caused by melting snow and ice.
   d) Tropical/Mediterranean climate zones have distinct wet and dry seasons, desert zones have dried river systems.
2. Size of the River
   a) Large rivers can have complex regimes from varied catchments.
3. Precipitation
   a) The amount, type, pattern and intensity.
   b) Regimes often reflect rainfall seasonal maxima or when snowfields or glaciers melt (Late spring/ Early Summer).
4. Temperature
   a) Evaporation is marked in summer with higher temperatures.
   b) Climate change will mold annual river regimes.
   c) River regimes are annual so large fluctuations will be due to seasonal change.
5. Geology and overlying soils
   a) Permeability and porosity as water can be stored as groundwater in permeable rocks and is released to the river through base flow with a regulated flow during dry periods.
6. Amount and type of vegetation cover
   a) Wetlands can hold water and release it very slowly into the system.
7. Human influences
   a) Dams building can regulate the flow.

Question 29

What is the river regime of the River Nile?

Answer 29

RIVER NILE REGIME

1. Shaped by the interaction between climate and geography across the basin.
   a) Drainage basin cover 10% of Africa and stretches across 35 degrees latitude, crosses climate zones ranging from high rainfall of tropical grasslands (extensive wetlands) to arid desert (barren desert) conditions.
   b) Hydrological characteristics of the River Nile at any location are affected by upstream geographical and climatic conditions.
2. The water of the River Nile originates from two major sources both within humid regions, rainfall averages 1,000 mm per year. Only covering a mere 20% of the basin.
   a) The mean water discharge is 2,800m^3/s.
   - The Equatorial Lakes Plateau, White Nile (30%).
   - Highlands of Ethiopia and Eritrea, Blue Nile (56%) and Atbara (14%).
   b) Yet in some parts of Egypt rainfall drops to less than 20 mm per year.
   - Nearly 50% of the river Nile flows through areas with low to no rainfall.
   - Discharge of the Blue Nile and Atbara exhibits high seasonal variation due to the seasonal rains over the Ethiopian highlands, which ultimately leads to annual Nile flooding.
   - And most precipitation falling in the Nile basin is lost to evaporation, seepage and overflow into wetlands each year.
   - So discharge of the River Nile is low compared to other large rivers even though it is the world’s longest river

Question 30

What is a storm hydrograph and the 2 different types?

Answer 30

STORM HYDROGRAPH

• Shows variation in a river’s discharge at a given point over a short period of time (usually before, during and after a storm).
• The shape of the storm hydrograph changes as a result of physical and human factors and can be described as either flashy or subdued.
• Can show how a river responds to a particular storm and is useful for predicting flood risk and comparing drainage basins responses to a heavy precipitation event.
• Climate change is likely to change hydrographs by making precipitation more intense in the Northern Hemisphere and drier in tropical areas.

1. Flashy Hydrograph - Indicate that there is a rapid increase in discharge, and perhaps a high risk of a sudden flood.
2. Subdued/Attenuated Hydrograph - Indicates that there is a limited increase in discharge following a weather event.

Question 31

What is the various terminology associated with a storm hydrograph diagram?

Answer 31

STORM HYDROGRAPH TERMINOLOGY
1. Normal (Base) Flow - The normal, day to day discharge of a river.

2. Storm Runoff - The part of the river flow derived from the immediate rainfall event. The most rapid transfer of water occurs overland and via throughflow.
3. Rising Limb - The increase in discharge in response to surface runoff and throughflow from a rainfall event, until peak flow is reached. When the storm begins, the river’s initial response is negligible as the precipitation takes time to reach the channel.
4. Falling (Recessional) Limb - The decline in discharge that occurs after peak flow. This segment is usually less steep than the rising limb because throughflow is being released relatively slowly into the channel.
5. Lag Time - The difference in hours and minutes between the time of maximum precipitation and the time of peak discharge. The lag time varies according to drainage basin conditions. Rivers with a short lag time tend to experience a higher peak discharge and they are more prone to flooding than rivers with a long lag time.
6. Approach Segment - The discharge of the river before the storm (the antecedent flow rate).
7. Peak Discharge - The maximum discharge by a stream or river in response to a rainfall event.
8. Bankfull Discharge - Occurs when a river’s water level reaches the top of its channel. Any further increase will result in flooding of the surrounding land.

Question 32

What factors determine the shape of a storm hydrograph?

Answer 32

STORM HYDROGRAPH FACTORS

1. Drainage Basin Size.
   a) Small basin size: water will reach the channel rapidly.
   b) Large basin size: water has a further distance to travel, longer for peak flow to occur.
2. Drainage Basin Shape.
   a) Circular basins: it will take less time for the water to reach the channel as all the extremities are equidistant from the channel.
   b) Elongated basins: it will take longer for the extremities to reach the channel.
3. Drainage Basin Relief
   a) Steep slopes: water flows rapidly downhill, reaching the channel faster.
   b) Gentle slopes/flat terrain: water can infiltrate into the ground and travel slowly through soil and rock.
4. Soil Type
   a) Low infiltration: clay and thin soils have low porosity and the grains swell when they absorb water, so water infiltrates slowly. And thin soil becomes saturated quickly.
   b) High infiltration: sandy and thick soils have a higher porosity, so the water can infiltrate. Deep soils allow more infiltration.
5. Geology Type
   a) Impermeable rocks: (granite) water cannot percolate into the rock, increasing surface runoff to the rivers.
   b) Permeable rocks: (limestone) water percolates through pore spaces and fissures into the groundwater store.
6. Drainage Density
   a) High drainage density: a large number of surface streams per km² means the stormwater will reach the channel rapidly.
   b) Low drainage density: a small number of surface streams per km² means the water travels slowly through the soil and rock to the river.
7. Natural Vegetation
   a) A low density/sparse vegetation: such as thin grass means low levels of interception and rapid movement of water.
   b) Densely forested woodland: deciduous in summer means more interception with more water lost to evapotranspiration from the surface of vegetation and slower movement of water.
8. Land Use
   a) Heavily urban and deforested: Concrete surfaces and roads have a lower permeability, and drains often carry water directly to the river. Ploughing furrows up/downslope increases runoff.
   b) Rural and reforested: Vegetated surfaces intercept water and allow infiltration so water travels slowly to the river channel.
9. Water Management
   a) No Intervention: Unregulated flow means shorter lag time as rainfall will reach the river faster.
   b) Intervention: Dams regulates flows downstream and abstraction lowers groundwater levels, increasing percolation.
10. Precipitation Intensity
    a) High Intensity: when precipitation exceeds the infiltration capacity of the soil, surface runoff occurs and transports river rapidly to the channel.
    b) Low Intensity: steady precipitation can infiltrate into the soil and then travel slowly through the soil to the river channel.
11. Precipitation Duration
    a) Prolonged: the water table rises and the soils become saturated, causing surface runoff.
    b) Short duration: most of the water infiltrates into the soil and travels at a slower pace.
12. Snowfall
    a) Rapid snowmelt: meltwater can not infiltrate into the frozen ground, so it flows rapidly over the surface into the channel.
    b) Gradual snowmelt: the ground thaws with the snow, so the meltwater can infiltrate into the soil and rocks before reaching the channel.
13. Evapotranspiration
    a) Lower rates/temperatures: fewer losses from the drainage basin system will increase the discharge.
    b) Higher rates/temperatures: high evapotranspiration losses will reduce discharge into the river channel.

Question 33

What is the role of planners in managing land use?

Answer 33

PLANNERS IN LAND USE

1. UK planners are required to determine whether any proposed development will influence flood risk with the change in land use, the National Planning Policy Framework (NPPF) sets out strict guidelines.
   a) Decisions vary depending on how much weight is given to environmental factors versus economic development (as it’ll increase the likelihood of higher flow and faster response time).
2. Building activity leads to the clearing of vegetation, which exposes soil and increases overland flow.
   a) Drains and sewers are built, which reduce the distance that stormwater must travel before reaching the channel.
   b) Urban rivers tend to be channelised with embankments to guard against flooding, yet can often be more devastating as the river overtops defences in a very confined space.
   c) Bridges can restrain the free discharge of floodwaters and act as local dams for upstream floods.
3. SuDS (Sustainable Drainage Systems) have been introduced to reduce runoff produced from rainfall such as:
   a) Green roofs - vegetation planted on a waterproof membrane to absorb and store rainfall.
   b) Permeable pavements - infiltrate rainwater.
   c) Filter drains - trenches filled with gravel, runoff storage and delay runoff time.
   d) Detention basins - depression in the land which delays storm runoff.