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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
The drainage basin hydrological cycle
The drainage basin hydrological system
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Source: http://www.alevelgeography.com
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
• 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.
The drainage basin hydrological cycle
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
• 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
The drainage basin hydrological cycle
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
• 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.
The drainage basin hydrological cycle
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
• 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.
The drainage basin hydrological cycle
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
• 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
The drainage basin hydrological cycle
Rainfall-runoff processExccess precipitation, after all losses flows through surface, subsurface and groundwater pathways into stream network , waterbodies to the watershed outlet
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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,..)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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Land – Atmosphere interactions
• Precipitation
• Evaporation + Transpiration = Evapotranspiration
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𝑷 − 𝑬𝑻 − 𝐺 − 𝑅 = ∆𝑆
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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Precipitation
• Precipitation
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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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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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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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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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Evapotranspiration
Overview of models
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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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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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Infiltration methods
• Horton’s equation ‘moving curve’ method
• Green & Ampt model
• SCS CN method
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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Groundwater flow
• Movement of water between unsaturated and saturated zone
• Water available to plants
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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Groundwater flow
• Movement of water influenced by soil properties and water table differences
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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Runoff
• Total flow in a stream on measuring gage
• Groundwater contribution to a stream is baseflow
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Formation process of surface runoff
• 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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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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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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Erosion – Top ten most used parameter in methods
Source - N. Dragičević, 2014
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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Water, land and anthropogenic influences?
• Pollution…
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Freshwater and pollution - sources and pathways of diffuse water pollutants
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Pathways of diffuse pollutants
Diffuse pollutants move into waters through:
• overland runoff;
• direct access to waters
• leaching to groundwater
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Nutrients - land phase
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Nutrients – sources and pathways
In streamUptake and releaseDepositionTransport
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Pathogens
• animals wastes and agriculture
• e.g. Escherichia coli.
• Pathways:• Surface runoff
• Leaching to groundwater
• Ammonia deposition
• Well casings
• Macropore flow
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Pesticides
• Main source• agriculture
Source: Ritter et all, 2002
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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).
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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).
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Attenuation of diffuse pollutants
• through interception mechanisms and BMPs adjacent to, and in, streams.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Modeling contaminants
• 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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
SWAT Modeling methods for water quality
Modeling contaminants
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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
Thank you
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.
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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