Introduction to hydrology 10.11.2015

H-ESD : Environmental and Sustainable Development

Michael Staudt, GTK

Table of contents

1. Elements of hydrologic cycle, Hydrology vs. Hydrogeology2. Hydrogeology, Origin and occurence of groundwater, water table2.1 Aquifer, aquicludes and aquitards2.2 Porosity and permeability2.3 Flow through soil and rocks3. Groundwater contamination and mining 4. Wells

1. Water

Water (H2O) is extraordinary in that it coexists on Earth in 3 distinct forms or states, 1: dry solid (ice), 2: wet liquid (water) and, 3: dry, invisible gas (vapor).

• Dipol • Van der Waals bonds• strong cohesion

1.1Elements of hydrologic cycle

1.1Elements of hydrologic cycle

All Water on EarthOceans__________________97.24%All ice caps/glaciers________2.14%

Groundwater_______________0.61%Freshwater lakes__________0.009%Inland seas/salt lakes______0.008%Soil Moisture_____________0.005%Atmosphere______________0.001%

All rivers_________________0.0001%Total____________________100%

Useable Freshwater on EarthGroundwater________________0.61%Freshwater lakes___________0.009%Rivers___________________0.0001%Total____________________0.6191%Adding ice caps/glaciers______2.14%Total____________________2.7591%

• Saturated zone is the subsurface zone below the water table where openings are filled with water under pressure greater than that of the atmosphere.

• Unsaturated zone is that part of the geological stratum above the water table where interstices and voids contain a combination of air and water; synonymous with zone of aeration or vadose zone

1.2 Evapo-Transpiration

Evaporation: water molecules exchanged between liquid and vapor state Transpiration: water added to the atmosphere by vegetationTotal water loss: Evapo-Transpiration

Condensation: needs a nucleus or surface to form when relative humidity is reaching 100% and the air is cooled without losing moisture: dew, frost

1.3 Precipitation

Occurs when 1. A humid air mass is cooled to the dew point

temperature2. Condensation or freezing nuclei must be present 3. Droplets must be coalesce to form raindrops4. The raindrops must be of sufficient size when they

leave the clouds

An Introduction to Rivers

Streams and rivers are part of the hydrologic cycle– Evaporation of water from Earth’s surface– Water returns to ocean underground or across the land

Runoff – Surface drainage

• Streams merge into tributaries and then into rivers

Drainage basin, watershed, river basin, or catchment– Area drained by a single stream

An Introduction to Rivers, cont.

Gradient is slope of river – is shown on longitudinal profile

Steep at high elevations– Headwaters

Decreases as river reaches base level– Lowest elevation of river, ultimately the ocean– Floodplain

• Flat surface adjacent to channel

Figure 6.9

Figure 6.11 Figure 6.12

Velocity, Discharge, Erosion and Deposition

Rivers are the primary transportation and erosion agent in the rock cycleAmount of erosion and deposition depends on stream velocity and discharge

– Volume of water flowing through a cross section per unit time (cubic meters per second)

– Discharge is constant along river– Changes in area lead to changes in velocity– Narrow channels have higher velocity than wide ones

Stream flow widens and slows when moving from high to low gradient– Forms an alluvial fan or delta

Materials Transported by Rivers

Rivers transport materials along with waterTotal load consists of:

– Bed load in [kg/s] or [m3/s]• Materials that roll, slide, bounce along bottom

mass of bed load ~ longitudal slope * mass of water (Marx, 2000)

mean grain diameter

– Suspended load in [g/m3]• Silt and clay particles that are carried in the water

– Dissolved load in [mg/L]• Materials carried as chemical solution

Characteristics of river flow

Hydrographs: Flows plotted over time, measured values usually on a daily basis for one year; averaging for monthly or annual meansDuration curves: Discharges of the hydrograph ordered according to magnitude over time. Gives an averaged period of time during which a specific flow rate is not exceeded

Source: Marx, 2000

How to measure water levels?

Balke, 1999

Water levels of a river

Balke, 1999

Stream discharge

How to measure flow velocity?

Balke, 1999

Channel Patterns and Floodplain Formation

Braided channels– Contain sand and gravel bars that divide and unite a single channel– Tend to be wide and shallow

Meandering channels– Migrate back and forth within a floodplain– Velocity is greater on the outside of curves causing erosion (cut banks)– Rivers slow on the inside of curves causing deposition (point bars)– Floodplains are created during overbank flows– During avulsion streams shift position– Contain pools and riffles

Figure 6.14

Flooding

Natural process of overbank flow

Related to:

– Amount and distribution of precipitation in drainage basin– Rate at which the precipitation soaks into earth– How quickly surface runoff reaches river– Amount of moisture in the soil

Causes of flooding

Source: Smith, 2004

Flood Description

Flood discharge – discharge of the stream at the point where water overflows the channel banksFlood stage – height of water in the riverShown on hydrograph

– Graph of stream discharge or water depth over timeFlood stage

– Elevation of water surface that is likely to cause damage to property

Recurrence interval– Average time between flood events of a certain size

Flash Floods

Typical in upper portion of drainage basin and in small basin of tributaries of larger rivers

Caused by intense rainfall of short duration over a relatively small area

Common in arid environments with steep slopes or little vegetation and following breaks of dams, levees, and ice jams

Most people who die during flash floods are in cars

Downstream Floods

Cover a wide area

Usually produced by storms of long duration that saturate the soil and produce increased runoff

Can be caused by combined runoff from thousands of tributary basins

– Characterized by large rise and fall of discharge at a particular location

Figure 6.20

Geographic Regions at Risk

Any place that receives precipitation has the potential to floodFloods are number-one disaster in the United States in twentieth centuryAll areas of the United States and Canada are vulnerable to floods

– A single flood can cause billions of dollars of property damage and more than 200 deaths

No of major floods in Europe

Flood events in Europe

ESPON 1.3.1Project, 2004

Floods recurrence in Europe

ESPON 1.3.1Project, 2004

Floods from 1950-2005

Source: Barredo, 2007

1 to 23: flash floods, 24 to 44: river floods, 45 to 47 storm surge floods. A triangle feature represents very large regional events. No major flood events were reported during the study period in the EU's regions not included in the map.

Effects of Floods

Primary– Injury and loss of life– Damage caused by currents, debris, and sediment to farms, homes, buildings, railroads, bridges, roads– Erosion and deposition of sediment related to loss of soil and vegetation

Secondary– Short-term river pollution of rivers– Hunger and disease– Homelessness

Factors Affecting Flood Damage

Land use on floodplainDepth and velocity of floodwatersRate of rise and duration of floodingSeasonQuantity and type of sediment depositedEffectiveness of forecasting, warning, and evacuation

Linkages with Other Natural Hazards

Primary effect of hurricanesSecondary effect of earthquakes and landslidesFires

– Produce shorts in electrical circuits and erode and break natural gas mains

Coastal erosion

Human Interaction—Land Use Changes

Rivers generally maintain a dynamic equilibrium– Balance between gradient, cross sectional shape, and flow velocity for

sediment load• That is, increase or decrease in the amount of water or sediment received by a stream changes gradient or

cross-sectional shape, changing the velocity

Land use changes can affect that equilibrium– Forest to farming creates more erosion and sediment– Sediment will build up the gradient of the stream– Stream will flow faster until it can carry greater amount of sediment– Farming to forest sets the opposite into effect

Figure 6.23 Figure 6.24

Human Interaction—Dam Construction

Upstream water slows down, deposits sediment, forming a deltaDownstream water devoid of sediment, will erode sediment to transport

– Slope of the stream will decrease until equilibrium is reached

Figure 6.25

Human Interaction—Urbanization

Increases magnitude and frequency of floods

Urban areas have impervious cover and greater storm sewers– Carries water to stream channels more quickly– Decreases lag time

• Causes flashy discharge – rapid rise and fall of floodwater

Reduces stream flow during dry season– Less groundwater is available

Bridges block debris creating dams and flash flooding

Minimizing the Hazard—Physical Barriers

Include earthen levees, concrete flood walls, reservoirs, and storm water retention basins

Levee breaks cause higher energy flows and bottlenecks in upstream areas

All physical barriers need to be maintained

Minimizing the Hazard—Channelization

Straightening, deepening, widening, clearing, or lining existing stream channels

– Can improve navigation and decrease flooding

Some drawbacks:– Drainage adversely affects plants and animals– Cutting trees eliminates shading and cover for fish and wildlife– Cutting trees eliminates many habitats– Changing the streambed destroys both the diversity of flow patterns and

feeding and breeding areas for aquatic life– Degrades the aesthetic

Figure 6.33

Minimizing the Hazard—Channel Restoration

Create a natural channel by allowing the stream to meander and reconstruct variable water flow conditions by:

– Cleaning urban waste to allow channel to flow freely– Protecting existing channel banks by not removing trees– Planting additional trees or vegetation where necessary

Perception of Flood Hazard

Most individuals have inadequate perception of flood problem

Local governments have prepared maps of flood prone areas

Federal government encourages local governments to adopt floodplain management plans

Public safety campaigns have been created to educate public about flash flooding

Adjustments to the Hazard—Flood Insurance

Maps of 100 year floodplain created to determine risk– Areas where there is a 1 percent chance of floods in any given year

New property owners required to purchase flood insurance

Building codes limit new construction on floodplain in some countries

– Codes prohibit building on 20 year floodplain

Figure 6.40

Flood recurrence calculation

Source: Keller

Recurrence Calculation

R = N+1/M

R: Recurrence interval in yearsN: Magnitude where M=1(ranking) is the highest discharge on recordM: Total number of records

Flood hazard zone I

Active floodplain areaProhibit development (business and residential) within floodplainMaintain area in a natural state as an open area or for recreational uses only

Flood hazard zone II

Alluvial fans and plains with channels less than a metre deep, bifurcating, and intricately interconnected systems subject to inundation from overbank flooding

Residential densities should be lowFlood proofing to reduce loss to structuresDry stream channels should be maintained in a natural stateInstallation of upstream water retention basins

Flood hazard zone III

Disected upland and lowland slopes, drainage channels where both erosional and depositional processes are operative along gradients less than 5%Similar to Flood hazard zone 2Roadways should be reenforced to withstand the erosive power of a channeled stream flow

Flood hazard zone IV

Steep gradient drainages consisting of incised channels adjacent to outcrops and mountain frontsBridges, roads and culverts should be designed to allow unrestricted flow of boulders and debrisAbandon roadways which are presently occupy the wash flood plainsRestrict residential dwelling to relatively level building sitesProvisions for subsurface and surface drainage on residential sitesStormwater retention basins in upstream channels

After Kenny (1990) in Bell ( 1993)

Adjustment to the Hazard—Flood Proofing

Raising foundation of buildings above the flood hazard

Constructing flood walls or mounds

Using waterproofing construction

Installing improved drains and pumps

Adjustment to the Hazard—Flood Plain Regulation

Obtain the most beneficial use of floodplains while minimizing flood damage and cost of flood protection

– Structural controls may be necessary on heavily used floodplains– Less physical modification of river is ideal

Flood hazard mapping– Shows location of previous flooding– Helpful in land use planning

Relocation– Government purchasing and removing homes damaged by

floodwaters

Table 6.2

References – Hydrology

Barredo, J: Major flood disasters in Europe: 1950–2005, Nat Hazards (2007) 42:125–148, SpingerBell, F. : Engineering Geology, 1993Keller, E. & DeVecchio , D. : Natural Hazards, Earth’s Processes as Hazards, Disasters, and Catastrophes, 2nd & 3rd ed., Chapter 6, Lecture presentation, Pearson Education Inc, 2008 & 2012Balke, K.-D.: Regional Hydrogeology,Lecture notes, 1999Marx, W.: Introduction to Hydraulic Engineering,Lecture notes, 2000ESPON 1.3.1 project, GTK, 2004JRC website: http://floods.jrc.ec.europa.eu/flood-risk/flood-disasters.htmlSmith, K: Environmnetal Hazards- Assessing Risk and Reducing Disaster, 4th edition, 2007

References – Hydrogeology

Bell, F.G.: Engineering Geology, Chapter 4, Blackwell Scientific Publications, 1993

Hölting, B.: Hydrogeologie, 4. Auflage, Enke, 1996

Fetter, C.W: Applied Hydrogeology, Fourth edition, Prentice Hall, 2001

Younger, P.L et al : Mine Water: Hydrogeology, Pollution, Remediation, Kluwer Academic Publishers, 2002