THE LAPSE RATE

The Lapse Rate

ELR Is The Decrease In Temperature With An Increase In High.

ELR Is 6.5◦C Per 1000m. (According To Air Conditions)

It Is Vary Due To Such Factors

Height, ELR Is Lower Near the Ground-Level; (Over Continental Areas; And Between Air Masses; Albedo Moisture).

When Water Vapor Raises, The Temperature Decreases, Air Is Much Cooler And The Ground Level Is Hotter. As The More Air Rises Cooler Sinks. During The Rainy Season/Lower in Winter Water Vapor Cannot Raises There Will Be No Air And the Wind Is Cooler.

ADIABATIC LAPSE RATE:

Parcel Of Air Rises During The Day, As It Heats Up Land; The Air Is Evaporated, So Water Vapor Rises.

Decrease In Pressure – As The Hot Air Raises, Pressure Will Be Dropped.

Increasing Volume (Air) & Increases in Temperature Making It Cools.

Ground Layer Is Heated By Insolation Land, Plant Is Heated Up.

As Warm Air Rises By An Increasing Energy, They Give Out Heat, So The Warm Air Is Converted To Cool.

Ground Layer Trapped Heat, Then Evaporates, Creating Parcel Of Air And So, Pressure Force To Rise, And Goes Low As It Reach Higher Level.

ADIABATIC LAPSE RATE

When The Dry Air Is Not Saturated, the Humidity Is Low, Meaning Less Water Vapor

At 1000 M, The Temperature Decrease, The Warm Air Raising So, There Is Moisture At The Point Of Condensation. At The Point Of Condensation. As It Reaching Dew Point, The SALR Occurs.

DALR It does not condenses DALR contains latent heat, as so the heat is not release. As the heat is not heated up, the air , day & temperature cools down at 0 DC As more energy to rise, there will be dry air. DALR is much cooler than SALR due to its less moisture. At ground-level, the air is heated up and until it reaches at 500m, it condense.

SALR 100% RH lots of moisture has to be released. The air is saturated after it condenses. How are the air changes to SALR? As the air pass through the condensation level, the latent heat release and the temperature is dropped, so the air is cool at 3 DC, it saturated. *DC (Degree Celsius).

DALR, As The Air Isn’t Condense, Latent Heat Is Not Release So, And The Higher The Parcel Of Air There Is Decrease In Temperature.

DALR Is Stay Unsaturated; It Force To Rise Or Warm Up At The Higher-Level, It Still Cool But, As If The Cooler Decrease To Its Lower Level It Will Be Warmer.

When The Parcel Of Air Rises, The Temperature Will Drop And The Energy Is Used Up, The Air Will Be Cooler.

As There Is No Heat To Be Release Due To Shortage Of Energy, The Air Started To Saturate. Warm Air Absorbs More Water Vapors/Moisture.

It Must Be Condensed Before Heat Release, If It Isn’t Condensed, There Will Be No Heat To Release.

DALR Decrease at the Lowest 9.8 DC.

If The Temperature Falls Below 0’c, The Air Is Cool, And As Called As Freezing Rate.

 DRY ADIABATIC LAPSE RATE

THE STATE OF STABILITY

When Rising Parcel Of Unsaturated Air Cools More Rapidly Than The Surrounding Air.

The Higher In Temperature Forcing The Parcel Of Air To Rise. The Cooler It Gets, It Will Sinks Because It Is Heavy And It Has No Saturated Air And No Condensation: Meaning No Release Of Latent Heat, The Air Is Dry, No Warm Air At Higher Altitude And So Parcel Of Air Raises As DALR Of 9.8’C Per 1000m. By The Time As The Rising Air Has Reached 1000m, It Has Cooled To 10.2’C Leaving It Cooler And Denser Than The Surrounding Air Which Has Cooled To Only 14’C.

At The Right Side, Shows The Rising Of Parcel Air Which Is Cooler. At 1000m, The Rising Air Of DALR Is Colder Than ELR (High Of 1000m, Temperature Is Low). As If There Is Nothing To Force The Parcel Of Air E.G. Mountains Or Fronts, It Will Sinks Back To Its Starting Point. This Air Is Described As Stable Air Because There Is No Condensation, But Only Shallow Flat-Top Cumulus Cloud, No Rainfall, And The Cooler Air Has To Move Back And Cooler Air Sink During Dry Sunny Weather Condition.

ELR At The Right Side, Air Goes Up In Temperature So There Is Increase In Temperature And Giving Its Cooler. ELR Is 6’C, And Does Not Sink To Much.

THE STATE OF INSTABILITY

ELR /DALR/ SALR

Green Line Shows ELR (Surrounding Area) For E.G. In Hot Summer Day 11’c Per 1000m.

DALR Is Warmer Than ELR For About 1.2’C (Warmer Air Force To Rise)

SALR At 5’C Per 1000m Had Reached Condensation Level At 15.1’C (Decrease In Temperature), The Air Is Cooler And It Release Latent Heat At 100% Of Relative Humidity.

As Dew Point Has Reached, The Cumulonimbus Cloud Is Formed At Instability Conditions.(500m Condensation Level)

Red Line Shows DALR, The Air Are Coming From The Ground, Bringing Warmer Air Reaching The Higher Latitude At 1000m, Giving It Cooler Air. DALR Is Still Rising As There Is Yet No Condensation. As The Dew Point Reached At 1000m, Temperature Started To Decrease.

ELR Always Present, When ELR Is Higher, Temperature Became Decrease.

From 20 Is Decrease To Its Final Temperature, Meaning The Air Is Become Cooler As It Temperature Decreases.

The Left Side Is Much Cooler Than The Right Side.

INSTABILITY AND STABLE CONDITION

At The Ground Level, The Temperature Is High About 20’C DALR (Warm Water Is Rising), As It Goes Up The Temperature Become Lower, DALR Is Cooler, ELR Is Unstable And No SALR Yet. Both DALR & ELR Are Cooler Especially At Higher Latitude, Where The Temperature Drops.

Since There Is Not Enough Air Moisture To Condense, No DALR, So It Is Saturated. DALR Has Moved To Right Side.

SALR Is Warmer Due To The Release Of Latent Heat. For Example In Britain. After Condensation Taking Place, There Will Be Cloudy Conditions And Heavy (Shallow)

DALR Is Cooler Than ELR (Stable Air)

Left DALR Is Constant At Right Much Cooler Than Surrounding Air And So, The Air Is Forced To Rise At Condensation Level, But There Is Still No SALR Yet, Temperature Decrease And ELR Also, It Is Cooler Than Before.

At 7.5’C, Condensation Taking Places, SALR Has Occurred. There Is A Change ELR Moved To The Left (Cooler) And SALR Is Warmer, So The Air Is Unstable. 

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RIVER PROFILES

The Hydrological Cycle

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This describes the process whereby water in its various forms is continually cycled between the land, sea and atmosphere. It also makes its way into the biosphere to influence animal and plant ecosystems around the globe.

A systems approach

This is a common approach in geography and the two main examples in this topic are:

The hydrological cycle: a closed system.

The drainage basin system: an open system.

Both consist of transfers, stores, inputs of water but the hydrological cycle is a closed system as no gains or losses from outside are added to the system.

The drainage basin system is said to be open as both inputs and outputs of energy and material occur. All systems in their natural state aim to be in a state of balance (dynamic equilibrium) as this is when they function best. Heavy rainfall, drought and human activity such as deforestation can easily upset the balance.

Within the hydrological cycle, four main processes operate:

1. Interception

This is when plants prevent some rainfall from directly reaching the ground, for example, water on leaves or foliage. It may later reach the floor via stem flow (water flows down the stem to the ground) or through-fall, where water drips to the ground. Secondary interception occurs at ground level where water hits undergrowth. Some water returns to the atmosphere via evapotranspiration.

2. Evapotranspiration

Water lost from vegetation via both evaporation and transpiration. Click on the boxes below to reveal definitions of both terms:

Potential Evapotranspiration:

The amount of water that could be lost by evapotranspiration. For example, this is potentially high in deserts, but the amount that can take place is limited due to the minimal moisture available. Actual evapotranspiration is what actually occurs. In the UK there is more water available for evapotranspiration than takes place.

3. Infiltration

Where water slowly soaks into the soil from the ground. The maximum rate at which this can occur is known asinfiltration capacity (mm/hour) and it is dependent on the amount of water already present in soil structure and vegetation.

4. Precipitation

The most important input into the system forms includes snow, hail, rain, and fog.

Percolation:

Water in the soil does not remain there but moves down slowly into the lower layers of soil and rock. It creates groundwater storage found in rocks and this may later be moved sideways through the rock via groundwater flow.

Flow:

Water flows through the hydrological cycle in various ways:

Throughflow: where water moves downwards through layers of soil.

Channel flow: downhill movement of water in rivers.

Groundwater flow: Lateral movement of water from the water table.

Drainage basins

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The drainage basin - as stated earlier - is an example of an open system, and many of the terms above are central to it. Below is a flow diagram of the drainage basin system:

All rivers receive a water supply and the area of land this comes from is known as a drainage basin. The boundaries of the basin are known as the watershed and will usually be marked by areas of higher land.

Drainage basins have many different characteristics that influence how quickly or slowly the main river within them responds to a period of intense rainfall, these are outlined in more detail in the section relating to storm hydrographs.

Drainage patterns

Land is drained by rivers in a variety of ways these are exhibited as drainage patterns.

This is shown in the diagram below:

Drainage density

This relates to the number of streams in a particular drainage basin and can be measured by dividing total length of all streams in a basin (L) by its area (A). As a rule, the higher the drainage density (D) the more quickly water drains to a river.

D = total L/A

Characteristics of high and low-density drainage basins:

High density (+2km per km2)	Impermeable land surface, steep slopes, limited vegetation cover, limited rainfall, gentle slopes, large channel frequency (tributaries).
Low density (-2km per km)	Permeable rock, for example, chalk, much vegetation cover, limited rainfall, gentle sloes, lower channel frequency.

Storm hydrographs and river discharge

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Storm hydrographs are graphs that show how a drainage basin responds to a period of rainfall. They are useful in planning for flood situations and times of drought as they show the discharge (amount of water reaching channel via surface run-off, throughflow, and base flow) that originated as precipitation.

Reading the hydrograph

A great deal of information can be gleaned from a hydrograph and the interpretation of them is often tested in exam questions. The diagram below shows the main points:

Influences on the hydrographs and drainage basin

Drainage basins all have a variety of characteristics in terms of vegetation, geology, soil type and so on, all of which interact to influence how quickly or slowly river discharge increases after a storm. The table below outlines the major influences on hydrographs and drainage basins:

A	Size of basin, shape and relief	Size - the smaller the basin the less time it takes for water to drain to the river, resulting in a shorter lag time. Shape - the shape of basin that lends itself to most rapid drainage is circular. In a long, narrow basin water takes longer to reach the river. Relief - the steeper the basin the more quickly it drains.
B	Forms of precipitation	Heavy Storms - in such a situation, rainfall is often far in excess of the infiltration capacity of the soil leading to much overland flow, and rapid rises in river levels. Lengthy rainfall - leads to the ground being saturated and overland flow. Snowfall - until snow melts, potential discharge for a river is held in storage. Rapid melting can lead to flooding.
C	Temperature	High rates of evapotranspiration reduce amounts of discharge, and low temperatures can store water in the form of ice and snow.
D	Land Use	Vegetation - Important in reducing discharge as it intercepts precipitation and adds to rates of evapotranspiration. Roots of plants take up water reducing throughflow. Interception is less in winter in the UK due the shedding of leaves from deciduous trees. Flooding is more likely in deforested areas.
E	Geology	Rock type varies within drainage basins and can be permeable (allowing water through) orimpermeable (not allowing water through). Permeable rocks can be porous such as chalk that store water within them or pervious, such as limestone where water flows along bedding plains. Impermeable rocks encourage grater amounts of surface run-off and a more rapid increase in discharge than permeable rocks.
F	Soil	A control on the rate of infiltration, amount of soil moisture storage and rate of throughflow. Larger pore spaces as found in sand, allow for greater water storage and limit the risk of flooding.
G	Drainage density	As stated earlier, the higher the density the greater the risk of flooding.
H	Tides and storms	High spring tides (illustrated by the Severn Bore) prevent water from entering the sea and increase the risk of flooding.
I	Urbanisation	A major impact because of its alteration on the hydrological process. The main affects are shown on the diagram below. Click on the magnifying glass to see the graph in more detail.

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The water balance

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Introduction

This is the balance between inputs into a drainage basin and outputs. It is important for understanding the processes operating in a drainage basin and water balances throughout the year.

It is expressed as follows:

P = Q + E (+/- change in storage)

P = precipitation

Q = run-off

E = evapotranspiration

The diagram below illustrates the main features of the water balance:

Here are some questions and answers that will help you to learn to read the graph accurately:

In which months is there a water surplus?

Jan, Feb, Mar, Apr, Nov, Dec.

Why is there soil moisture recharge in October?

Due to the excess of evapotranspiration over precipitation in May - Sept.

When is field capacity attained?

November.

Why is a water deficit not shown on the graph?

Precipitation always far exceeds evapotranspiration.

Soil moisture

Surplus: If precipitation exceeds evapotranspiration and the excess is not been used by plants.

Deficiency: Evapotranspiration exceeds precipitation.

Recharge: Replacement of water lost during drier periods.

Field capacity

The maximum amount of water soil can hold.

A water surplus can result in wet soils, high river levels and run-off whereas a deficit leads to dry soil, falling river levels and possibly drought. Management is shown in the example at the end of this topic.

Water Deficit

Evapotranspiration is in excess of precipitation and any previously available moisture has been used, in soil moisture utilisation.

Variations in a river flow (regimes)

The regime of a river is expected to have a seasonal pattern of discharge during the year. This is due to factors such as climate, local geology and human interaction. Equatorial rivers have regular regimes but in the UK where seasons exist one or two peaks may be recognisable.

Simple regimes

These show times of high water levels followed by lower levels. They exist as a result of a glacier melt, Snowmelt, or seasonal rainfalls such as monsoons.

Complex regimes

If a river has more than one period of high water levels and/or low water levels, a more complex regime results. It is more common on large rivers that flow through a variety of relief and receive their water supply from large tributaries, for example, The Rhine.

A river has two main functions: one, to transport water and two, to transport sediment. The type of flow that occurs depends on factors such as gradient, volume of water, channel shape, and friction.

There are two types of flow:

Laminar Flow: This rarely occurs, water flows smoothly in a straight channel. It is most common in the lower parts of a river. It is shown in the diagram below:

Turbulent flow: This is far more common, it occurs where the shape of the rivers channel is varied with pools, meanders, and rapids. A great deal of turbulence results in sediment being disturbed. The greater the velocity the larger the quantity and size of particles that can be transported. Turbulent flow is illustrated in the diagram below:

  

Channels

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Channel roughness

It is often thought that the velocity of a river is greatest near its start. This is not the case, as large angular boulders create a rough channel shape and therefore, a large amount of its bed friction. This creates more resistance to flow than a river with smooth clays and silt forming its banks. The roughness coefficient is measured using Manning's 'n', which shows the relationship between channel roughness and velocity. The equation is as follows:

v = velocity

R = hydraulic radius

S = slope

n = roughness

A high-value indicates a rough bed.

Channel shape

The efficiency of a rivers channel is measured by finding its Hydraulic radius. It is the ratio between the length of wetted perimeter and cross section of a river channel.

Wetted perimeter: the entire length of the riverbed bank and sides in contact with water.

The examples below show the difference between an efficient river channel and an inefficient river channel:

Cross-section area:	Wetted perimeters:	Hydraulic radius:
Stream A = 400m2	Stream A = 18m	Stream A 40 / 18 = 2.22m
Stream B = 40m2	Stream B = 24m	Stream B 40 /24 = 1.66m

Channel slope

Steeper gradients usually lead to greater velocities, because of the influence of gravity.

The long profile

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Upper course

The characteristics of a river and its valley found in this course include vertical erosion, lakes, waterfalls, potholes, rapids and gorges. Overland flow is found in depressions making lakes. Eventually, the channel gets deeper and waterfalls become rapids.

Middle course

Characteristics include, lateral erosion, transportation, floodplain, meanders, truncated spurs, and river cliffs. The gradient of the river is increasingly even and smooth, and the flood plain begins to develop.

Lower course

Here, transportation and deposition are found. The channel is large and features such as Deltas, levees, bluffs and meanders are found. The flood plain increases in size as meanders migrate downstream.

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