hydrology - theory and general concepts · hydrology - theory and general concepts 1. the...

PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.

Hydrology - theory and general concepts

Dr. Potočki Kristina, CE

University of Zagreb

Faculty of Civil Engineering

Water Research Department


Hydrology - theory and general concepts

1. The hydrological cycle and water budget

2. Land – Atmosphere interactions• Precipitation

• Evapotranspiration

3. Infiltration

4. Groundwater flow

5. Surface flow

6. Open channel flow

7. Erosion


The drainage basin hydrological cycle

The drainage basin hydrological system

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Source: http://www.alevelgeography.com


Drainage Basin Flow Chart

Lakes/ Reservoars

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Source: http://www.alevelgeography.com

• The hydrologic cycle –processes and pathways of the water

• Solar energy


• When atmospheric conditions are suitable, water vapor condenses and forms droplets.

• Precipitation: deposition of moisture from the atmosphere to the surface. Can be: snow, rain, sleet, snow, hail, frost, fog...

• Evapo-transpiration: release of water vapour from the earths surface in the form of evaporation and transpiration.

• Interception: retaining of water by plant leaves, stems and branches. Water is stopped from reaching the soil directly.

• Stem-flow/leaf drip: water that travels through the stem of a plant.

• Surface runoff/overland flow: the flow of water over the surface of the ground.



• Precipitation falling on land surface enters into a number of different pathways of the hydrologic cycle:• some temporarily stored on land surface as ice and snow or

water puddles → depression storage

• some will drain across land to a stream channel → overland flow

• If surface soil is porous, some water will seep into the ground by a infiltration→ recharge to groundwater



• Below land surface soil pores contain both air and water →vadose zone or zone of aeration

• Water stored in vadose zone → soil moisture

• Soil moisture is drawn into rootlets of growing plants

• Water is transpired from plants as vapor to the atmosphere

• Under certain conditions, water can flow laterally in the vadose zone → interflow

• Water vapor in vadose zone can also migrate to land surface, then evaporates

• Excess soil moisture is pulled downward by gravity → gravity drainage

• At some depth, pores of rock are saturated with water →top of the saturated zone.



• Soil moisture storage: moisture held stationary in the soil.

• Through-flow: the movement diagonally downward of water through the soil.

• Percolation: the filtering of water downwards vertically through the joints and pores of permeable rock.

• Groundwater flow: water that flows horizontally underground through rock.

• Soil saturation: when the soil contains a lot of water.

• Field capacity: the volume of water which is the maximum the soil can hold.

• Infiltration rate: the rate at which water infiltrates into the soil.

• Water-table: the level below which the ground is saturated.



• Groundwater contribution to a stream → baseflow

• Total flow in a stream → runoff

• Water stored on the surface of the earth in ponds, lakes, rivers → surface water


Rainfall-runoff processExccess precipitation, after all losses flows through surface, subsurface and groundwater pathways into stream network , waterbodies to the watershed outlet


For any hydrological system, a water budget can be developed to account for various flow pathways and storage components. The hydrological continuity equation for any system is:

Where

Precipitation

SurfaceRunoff

Groundwater flow

Evaporation

Transpiration

Change in storage in specified time period

Water budget

𝐼 − 𝑄 =𝑑𝑆

𝑑𝑡

𝑑𝑆

𝑑𝑡- change in storage per time (L3/t)

I – inflow (L3/t)O – outflow (L3/t)


Watershed – spatial unit

• A watershed is a geographical unit in which the hydrological cycle and its components can be analyzed.

• Usually a watershed is defined as the area that appears, on the basis of topography, to contribute all the water that passes through a given cross section of a stream.

• Watershed - definition• Outlet Point

• Delineation - topography and real (e.g. karst)

• Artificial barriers (e.g. roads, reservoirs,..)


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Land – Atmosphere interactions

• Precipitation

• Evaporation + Transpiration = Evapotranspiration

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𝑷 − 𝑬𝑻 − 𝐺 − 𝑅 = ∆𝑆


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Precipitation

• Precipitation

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Precipitation

• Measured at points – gaging stations

• Estimated over watershed area –satellite, radar

• Time interval (from 5 min to total daily)

- gaging stations

Source: Ivanković, I. 2012


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Precipitation

• Part of the precipitation is lost through evaporation, with interception of the plants and within small depressions

• How to determine that amount? ET

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Precipitation

• Part of the precipitation is lost through evaporation, with interception of the plants and within small depressions

• How to determine that amount?

• Model of Potential Evapotranspiration (PET)

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Evapotranspiration

Factors affecting Evaporation

• Water temperature

• Air temperature above water layer

• Absolute humidity of air above water surface

• Wind – keeps absolute humidity low

• Solar radiation

Factors affecting transpiration

• A function of

• plant density

• plant size

• limited by soil water.

• Wilting point = surface tension of soil-water interface > Osmotic pressure.


Evapotranspiration

• Evapotranspiration – difficult to measure , a lot of regional variables

• Represents total water loss due to 1) free water evaporation, 2) plant transpiration, 3) soil moisture evaporation

• Potential evapotranspiration model – the water loss (expressed as water depth), which occur if at no time there is a deficiency of water in the soil for the use of vegetation

Models

• Energy based (e.g. Turc)

• Temperature based (Blaney-Criddle)

• Mass transfer methods (Penman)

• Composite (e.g. Penman-Monteith)


Evapotranspiration

Overview of models


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Infiltration

• Part of the precipitation that reaches ground can now start with two processes: surface runoff and infiltration into ground

• The process in which water is absorbed by soil during a rainfall

• The speed of infiltration is measured in the amount of water (mm or cm) absorbed per hour

• The infiltration capacity of a soil is high at the beginning of a storm and has an exponential decay as the time elapses.

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Infiltration

• Physically based models• Water movement in soils

in a simplified manner

• Focusing especially on humidity front level

• Depending on physical parameters

Author Function Legend

Horton f 𝑡 = 𝑓𝑓 + 𝑓0 − 𝑓𝑓 𝑒−γ

f 𝑡 - infiltration capacity during time [cm/s]𝑓0- initial inflitration capacity [cm/s]𝑓𝑓- final infiltration capacity [cm/s]

γ - constant depending on the soil type

Kostiakov f 𝑡 = 𝑓0𝑡−𝛼 α - constant depending on the soil conditions

Dvorak –Mezencev

f 𝑡 = 𝑓0 + 𝑓1 − 𝑓𝑓 𝑡−𝑏𝑓1 - inflitration cpacity time t=qmin [cm/s]t - time [s]b - constant

Holtan f 𝑡 = 𝑓𝑓 + 𝑐𝑤 𝐼𝑀𝐷 − 𝐹 𝑛c - factor variable from 0.25 to 0.8w - Holtan equation flow factorn - experimental constant, approximately = 1.4

Philip f 𝑡 =1

2𝑠𝑡−0.5 + 𝐴

s - sorptivity [cms-0.5]A - gravity component depending on

hydraulic conductivity at saturation [cm/s]

Dooge f 𝑡 = 𝑎 𝐹𝑚𝑎𝑥 − 𝐹𝑡

a - constantFmax - maximal retetion capacityFt - water quantity retained on soil at time t

Green&Ampt f 𝑡 = 𝑘𝑠 1 +ℎ0 − ℎ𝑓

𝑧𝑓 𝑡

𝑘𝑠 - hydraulic conductivity at saturation [mm/h]ℎ0 - surface pressure load [mm]ℎ𝑓 - pressure load at the humidity front [mm]

𝑧𝑓 - humidity front depths [mm]Source -Musy, 2001


Infiltration methods

• Horton’s equation ‘moving curve’ method

• Green & Ampt model

• SCS CN method


Horton Equation

• Empirical formula

• Infiltration tends to decrees exponentially when rainfall supply exceeds the infiltration capacity

𝑓𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 = 𝑓𝑐 + 𝑓0 − 𝑓𝑐 𝑒ൗ−𝑡𝐾

fcapacity = maximum infiltration capacity of the soilf0 = initial infiltration capacityfc = final (constant) infiltration capacityt = elapsed time from start of rainfallK = decay time constant

The actual infiltration rate must be equal to the smaller of the rainfall intensity i(t) and the infiltration capacity fcapac

𝑓 = 𝑓𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 for 𝑖 > 𝑓𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦𝑓 = 𝑖 for 𝑖 ≤ 𝑓𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦

f = actual infiltration rate (mm/hr or inches/hr)i = rainfall intensity (mm/hr or inches/hr).

Rainfallf, i

time

Infiltration curve


Green – Ampt infiltration model

• Green and Ampt method assumes:

- Homogenous soil (wetting at constant rate)

- Water content remains volumetric constant above and below wetting front

(completely saturated)

𝑓 = 𝐾 1 +𝑀𝑆

𝐾

M = moisture deficitS = suction headK = Hydraulic Conductivity

𝑀 = 𝜗𝑆 − 𝜗𝐼

𝜗𝐼 = Initial Moisture Content

𝜗𝑆 = Saturated Moisture Content

TransmissionZone

Saturated Zone

WettingZone Wetting

Front

Dep

th

Dep

th

SaturatedZone

Wetting Front

Moisture Content Moisture Content0 0

Actual infiltration Green & Ampt infiltration

𝜗𝑆

𝜗𝐼 𝑀

𝐿 SaturatedLength

𝜗𝜗

Green-Ampt model idealization of wetting front penetration into a soil profile


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Effective precipitation

• What is the amount of the precipitation, after all losses that will be part of surface runoff?

• SCS CN method

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Qef

t

Peff x A

Peff

A


SCS CN

• Soil Conservation Service (SCS) Curve Number (CN) method

• Very simple, represented as function of precipitation, soil’s permeability, water content of the soil

𝑸(𝑷𝒆𝒇𝒇) =𝑷 𝒕 − 𝑰𝒂

𝟐

𝑷 𝒕 + 𝑺 − 𝑰𝒂

𝑄 − depth of runoff – is equal Peff𝑃 − depth of rainfall𝐼𝑎 − initial abstraction𝑆 − potential storageCN − curve number for the day ≤ 100

𝑆 =25400

𝐶𝑁− 254 𝑚𝑚

The CN can be obtained from tables – soil type and moisture correlations

• The CN (Curve Number) method does not consider intensity and duration of rainfall, only total rainfall volume


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Groundwater flow

• Movement of water between unsaturated and saturated zone

• Water available to plants

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Groundwater flow

Groundwater Infiltration: Infiltration delivers water from

the surface into the soil and plant rooting zone. Occurs closer to the surface of the soil.

• Percolation: The flow of water from unsaturated zone to the saturated zone. Percolation moves it through the soil profile to replenish ground water supplies or become part of sub-surface run-off process

• Seepage: Seepage is the flow of water under gravitational forces in a permeable medium. Flow of water takes place from a point of high head to a point of low head. The flow is generally laminar.

• For example, water enters the ground surface at the upstream side of a retaining structure like a dam and comes out at the downstream side.


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Groundwater flow

• Movement of water influenced by soil properties and water table differences

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Water Table

Flow distance (l)

B

A

Elevation B:Water table =Y [m] above see level

Elevation A:Water table =X [m] above see level

DARCY’s LAW

𝑸 = 𝑨 𝑲𝒉

𝒍

K = Permeability(hydraulic conductivity)l = flow distanceh = vertical drop A = cross sectional area of flow

𝒉 = 𝑿 − 𝒀 A [m2]

Darcy’s Law

• Henri Darcy established empirically that the energy lost ∆h in water flowing through a permeable formation is proportional to the length of the sediment column ∆L.

• The constant of proportionality K is called the hydraulic conductivity. The Darcy Velocity VD:

VD = – K (∆h/∆L) and since Q = VD A (where A = total area)

Q = – KA (dh/dL)


Range of values of K

Medium K in m/s

Gravel 10-3 to 2

Sand 3x10-6 to 10-2

Typical Forest soil 10-7 to 10-5

Bog soils 10-9 to 10-7

Marine clay 10-12 to 10-9

Basal till 10-12 to 10-10

Igneous rock, shale 10-13 to 10-10

Sandstone 10-10 to 10-6

DARCY’s LAW

𝑸 = 𝑨 𝑲𝒉

𝒍


Porosity and Permeability

Porosity: Percent of volume that is void space.

• Sediment: Determined by how tightly packed and how clean (silt and clay), (usually between 20 and 40%)

• Rock: Determined by size and number of fractures (most often very low, <5%)

• Permeability is not proportional to porosity.

Sediment0 Porosity (%) Permeability

Gravel 25 to 40 Excellent

Sand (clean) 30 to 50 Good to Excellent

Silt 35 to 50 Moderate

Clay 35 to 80 Poor

Glacial till 10 to 20 Poor to Moderate


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Runoff

• Total flow in a stream on measuring gage

• Groundwater contribution to a stream is baseflow

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Runoff Hydrograph

• Graph of stream discharge as a function of time at a given location on the stream

Perennial river Ephemeral river Snow-fed River


Formation process of surface runoff

• Groundwater flow

• Subsurface flow (interflow)

• Overland flow

Runoff pathways

• Surface runoff

• overland flow (sheet flow)

• shallow concentrated flow

• open channel flow



• Total streamflow during a precipitation event includes the baseflow existing in the basin prior to the storm and the runoff due to the given storm precipitation. Total streamflow hydrographs are usually conceptualized as being composed of:

• DIRECT RUNOFF which is composed of contributions from surface runoff and quick interflow.

• BASEFLOW which is composed of contributions from delayed interflow and groundwater runoff.

• SURFACE RUNOFF includes all overland flow as well as all precipitation falling directly onto stream channels. Surface runoff is the main contributor to the peak discharge.


Formation process of subsurface and groundwater runoff

• Interflow is the portion of the streamflow contributed by infiltrated water that moves laterally in the subsurface until it reaches a channel. Interflow is a slower process than surface runoff. Components of interflow are:

• QUICK INTERFLOW, which contributes to direct runoff, and

• DEAYED INTERFLOW, which contributes to baseflow.

• Groundwater runoff is extremely slow process as compared to surface runoff.

• Basins with a lot of storage have a large recessional limb.

• Recession occurs exponentially for baseflow


Rational Formula / Method

• Widely used to estimate peak surface runoff rate for variety of drainage structures

• Mostly suitable for small urban watersheds without natural water storages such as swamps and pounds.

𝑄𝑝 = 𝑘 𝐶 𝑖 𝐴

k = unit conversion factor (1.008 for English unit; 0.27 for metric unit)Qp = peak discharge (ft3/s or m3/s)i = rainfall intensity (in/hr or mm/hr)A = drainage area (acres or km2)

i = average intensity of rainfall corresponding tothe duration of time-of-concentration

C= runoff coefficient is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received(0-1 values, Tables)


Time of Concentration

• Concept to measure the response of a watershed

• After precipitation begins, different areas of watersheds affect runoff at different times.

• Time of Concentration represents time at which all watersheds begin to contribute runoff

• Function of length and velocity

A

B

TCt2

t1

c = Rational method runoff coefficientG = Constant. FAA: G=1.8, Kirpich: G=0.0078, Kerby: G=0.8268k = Kirpich adjustment factorL = Longest watercourse length in the watershed [m]r = Kerby retardance roughness coefficient.S = Average slope of the watercourse [m/m].t = Time of concentration, [min].V = Average velocity in watercourse, m/min. V=L/t.

100%

% A

rea

time



• Groundwater flow

• Subsurface flow (interflow)

• Overland flow

Runoff pathways

• Surface runoff

• overland flow (sheet flow)

• shallow concentrated flow

• open channel flow


𝑸 = 𝒗𝑨

Area of the cross-section (m2)

Avg. velocity of flow at a cross-section (m/s)

Flow rate (m3/s)

Av

General Flow Equation

Open channel flow


Classification of Open-Channel Flows

Flow in open channels is also classified as being uniform or non-uniform, depending upon the depth y.

Uniform flow (UF) encountered in long straight sections where head loss due to friction is balanced by elevation drop.

Depth in UF is called normal depth yn


Manning Equation

▪ for open channels flow

𝑉 =1

𝑛𝑅ℎ

2/3𝑆01/2

Image Credits: http://www.geograph.org.uk/photo/5898965

Open channel flow example- River Avon, City of Bristol

In addition to being empirical, the Manning Equation is a dimensional equation, so the units must be specified for a given constant in the equation.

V = cross-sectional mean velocity (m/s)n = Manning coefficient of roughness - ranging from (Tables)Rh = hydraulic radius (m)S = slope - or gradient - of stream bed (m/m)Q = volume flow (m3/s)A = cross-sectional area of flow (m2)

𝑄 = 𝑉𝐴 𝑄 =1

𝑛𝐴𝑅ℎ

2/3𝑆01/2

Very sensitive to n


Manning roughness coefficient, n

Lined Canals n

Cement plaster 0.011

Untreated gunite 0.016

Wood, planed 0.012

Wood, unplanned 0.013

Concrete, troweled 0.012

Concrete, wood forms, unfinished 0.015

Rubble in cement 0.020

Asphalt, smooth 0.013

Asphalt, rough 0.016

Natural Channels n

Gravel beds, straight 0.025

Gravel beds plus large boulders 0.040

Earth, straight, with some grass 0.026

Earth, winding, no vegetation 0.030

Earth, winding with vegetation 0.050

n = f (surface roughness, channel irregularity, stage…)

There are numerous factors that affect n-values, including:

▪ Surface roughness ▪ Seasonal change

▪ Vegetation ▪ Suspended material

▪ Silting / scouring ▪ Bed load

▪ Obstruction ▪ Stage (depth of flow)

▪ Size / shape of channel ▪ Discharge


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Movement of water and land mass

• Erosion and land mass movement also present in watershed

• Production and transport of sediment

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Erosion

• EROSION is the wearing down of a landscape over time. It includes the detachment, transport, and deposition of soil particles by the erosive force of raindrops and surface flow of water.

Types of water erosion

• sheet erosion

• rill erosion

• gully erosion

• tunnel erosion

Source: https://www.agric.wa.gov.au/water-erosion/water-erosion-agricultural-region-western-australia


Erosion

Sheet erosion

• removal of a uniform layer of soil from the soil surface by shallow 'sheet’ surface flow over the ground surface

• small sediment deposits behind tufts of grass.

Rill erosion

• caused by soil detachment from concentrated run-off.

• numerous small channels of less than 30cm depth.


Erosion

Gully erosion - severe form of land degradation, affecting infrastructure, paddock management and property access

• Gullies - deep (>30cm), open, incised and unstable channels

• Tunnel erosion - Surface water flows into a dispersive subsoil through surface cracks, rabbit burrows, or old tree root holes


Erosion

• Methods:• Erosion Potential (Gavrilović) Method

• Factorial Scouring Model (FSM)

• Erosion hazard units (EHU)

• Soil Loss Estimation Model for Southern Africa (SLEMSA)

• CORINE erosion risk maps

• Coleman and Scatena scoring model (CSSM)

• Fleming and Kadhimi scoring model (FKSM)

• Wallingford scoring model (WSM)

• Universal Soil Loss Equation (USLE)

• Revised Universal Soil Loss Equation (RUSLE)

• RIVM Model

• INRA Model

• SCALES Model

• Fournier

• Water Erossion Prediction Model (WEPP)

• Soil and Water Assessment Tool (SWAT)

• Morgan Morgan Finney (MMF)

• Annualized Agricultural Non-Point Source Pollution (AGNPS)

• Modified Universal Soil Loss Equation (MUSLE)


Erosion – Top ten most used parameter in methods

Source - N. Dragičević, 2014


Erosion - MUSLE method (modified version of well known USLE)

• The modified universal soil loss equation (Williams, 1995) is:

𝒔𝒆𝒅 = 𝟏𝟏. 𝟖 𝑸𝒔𝒖𝒓𝒇𝒒𝒑𝒆𝒂𝒌𝒂𝒓𝒆𝒂𝒉𝒓𝒖𝟎.𝟓𝟔

𝑲𝑼𝑺𝑳𝑬𝑪𝑼𝑺𝑳𝑬𝑷𝑼𝑺𝑳𝑬𝑳𝑺𝑼𝑺𝑳𝑬𝑪𝑭𝑹𝑮

sed = sediment yield on a given day (metric tons)

Qsurf = surface runoff volume (mmH2O/ha)

qpeak = runoff rate (m3/s)

Areahru = area of the watershed or HRU (hydrological response unit) (ha)

KUSLE = USLE soil erodibility factor = 0.013 metric ton m2 hr/(m3-metric ton cm)

CUSLE = USLE cover and management factor

PUSLE = USLE support practice factor

LSUSLE = USLE topographic factor

CFRG = coarse fragment factor

The main difference compared to the USLE is the replacement of the rainfall factor with a direct estimate of surface runoff and peak runoff rate


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Water, land and anthropogenic influences?

• Pollution…

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Freshwater and pollution - sources and pathways of diffuse water pollutants


Sources of diffuse water pollutants

• Anthropogenic and natural contaminants occur in surface waters, groundwater, sediments, and ultimately in drinking water

• Two primary source categories:

(1) point-source pollution

(2) non-point-source (diffuse)pollution

NONPOINT SOURCES

Urban streets

Suburban development

Wastewater treatment plant

Rural homes

Cropland

Factory

Animal feedlot

POINT SOURCES


Sources of diffuse water pollutants

• Agriculture

• Pathogens

• Sediment

• Pesticides

• Atmosphere

NONPOINT SOURCES

Urban streets

Suburban development

Wastewater treatment plant

Rural homes

Cropland

Factory

Animal feedlot

POINT SOURCES


Pathways of diffuse pollutants

Diffuse pollutants move into waters through:

• overland runoff;

• direct access to waters

• leaching to groundwater


Agriculture

• Agriculture → Nutrients (N, P)

• The two predominant sources of nutrients in agriculture are animal wastes and fertilizers applied to crops.

• When fertilizers are applied to soil, the nutrients contained within them will either be taken up by the crop, remain in the soil, or be lost from the soil of the crop systems by one of several possible mechanisms (Marschner,1986)

• Leaching, runoff, and atmospheric transport are the primary mechanisms by which nutrients enter aquatic environments.

• Leaching is the most significant source of nitrates in groundwater

• Nitrogen leaching in soil depends on soil structure and porosity, water supply from precipitation and irrigation, evaporation from the soil surface, and the degree of drainage


Nutrients - land phase


Nutrients - land phase

Factor Less leaching More leaching

Crop Vigorous cropEstablished crop

Poor cropSeedbed application

Soil Heavy soilPoor drainage

Light soilGood drainage

Time of application(fertilizer)

At the beginning of the main growing period or during active crop growth

At the end of growing season or out of season

Climate Low rainfall High or irregularly distributed rainfall


Nutrients – sources and pathways

In streamUptake and releaseDepositionTransport


Pathogens

• animals wastes and agriculture

• e.g. Escherichia coli.

• Pathways:• Surface runoff

• Leaching to groundwater

• Ammonia deposition

• Well casings

• Macropore flow


Pesticides

• Main source• agriculture

Source: Ritter et all, 2002


Sediment

• Acting as both a source and a sink for many natural and anthropogenic contaminants.

• As sink - contaminants from point and nonpoint sources become entrained in sediments, either by partitioning out of the water or via deposition of suspended solids to which they are adsorbed.

• As a source - contaminated sediments may release chemicals to water via desorption from organic ligands into surrounding interstitial water.


Athmosphere

• Pollutant emissions to the atmosphere

• anthropogenic (released by human activities)• industrial stacks, municipal waste incinerators, agricultural activities (e.g., pesticide

applications) and vehicle exhaust

• natural (e.g., releases of geologically-bound pollutants by natural processes)• those associated with volcanic eruptions, windblown gases and particles from forest fires,

windblown dust and soil particles, and sea spray

• reemitted (e.g., mass transfer of previously deposited pollutants to the atmosphere by biologic/ geologic processes).


Athmosphere

• Pollutant loading to water bodies from the atmosphere primarily occurs through wet or dry deposition.

• wet deposition - removal of air pollutants from the air by a precipitation event, such as rain or snow.

• dry deposition - removal of aerosol pollutants through eddy diffusion and impaction, large particles through gravitational settling, and gaseous pollutants through direct transfer from the air to the water (i.e., gas exchange).


Attenuation of diffuse pollutants

• through interception mechanisms and BMPs adjacent to, and in, streams.


Modeling contaminants

Statistical approach

• USGS-SPARROW

• SPARROW (SPAtially Referenced Regressions On Watershed attributes) models estimate the amount of a contaminant transported from inland watersheds to larger water bodies by linking monitoring data with information on watershed characteristics and contaminant sources. Explore relations between human activities, natural processes, and contaminant transport using interactive Mappers.



• STEPL - USEPA

• Spreadsheet tool for estimating pollutant load (STEPL) - simple watershed and landscape model that requires minimal data preparation and no calibration.

• It is good for long averaging periods and it can be tested or validated.

• supported by United States environmental protection agency (USEPA)

• simple algorithms to calculate nutrient and sediment loads from different land uses and the load reductions that would result from the implementation of various best management practices (BMPs).

• STEPL computes watershed surface runoff, nutrient loads (nitrogen-N and phosphorus-P), 5-day biological oxygen demand (BOD5), and sediment delivery based on various land uses and management practices.


SWAT Modeling methods for water quality


Sediment routingControlled by deposition and degradation processesMax. amount transported - Function of maximum flow velocity

Nutrient routingMETHOD: In stream kinetics with QUALE 2 method (Brown and Barnwell, 1986)Nutrients dissolved in the stream – transported with the waterNutrients adsorbed to the sediment – transported/ deposited within channel

Channel pesticide routingSediment transformation in dissolved and sediment-attached METHOD: First-order decay relationshipModeled in stream processes: settling, burial, resuspension, volatilization, diffusion, transformation


Thank you


References

• Ritter, Keith Solomon, Paul Sibley, Ken Hall, Patricia Keen, Gevan Mattu, Beth Linton, L. (2002). Sources, pathways, and relative risks of contaminants in surface water and groundwater: a perspective prepared for the Walkerton inquiry. Journal of Toxicology and Environmental Health Part A, 65(1), 1-142.

• Dragičević, N. (2016). Model for erosion intensity and sediment production assessment based on Erosion Potential Method modification (Doctoral dissertation, Građevinski fakultet, Sveučilište u Rijeci).

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