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
Source: http://www.alevelgeography.com
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. 3 Drainage Basin Flow Chart
• The hydrologic cycle – processes and pathways of the water
Lakes/ Reservoars • Solar energy
Source: http://www.alevelgeography.com PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. 4 The drainage basin hydrological cycle
• 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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. The drainage basin hydrological cycle
• 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
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. The drainage basin hydrological cycle
• 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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. The drainage basin hydrological cycle
• 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.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. The drainage basin hydrological cycle
• 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 process Exccess 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. Water budget
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: 푑푆 퐼 − 푄 = 푑푡 Where 푑푆 - change in storage per time (L3/t) 푑푡 Evaporation I – inflow (L3/t) 3 O – outflow (L /t) Precipitation Change in storage in specified Transpiration time period Surface Groundwater Runoff flow
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. Land – Atmosphere interactions
• Precipitation • Evaporation + Transpiration = Evapotranspiration
P 푷 − 푬푻 − 퐺 − 푅 = ∆푆 ET
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. 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. Precipitation
• Part of the precipitation is lost through evaporation, with interception of the plants and within small depressions P • How to determine that amount? ET
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Precipitation
• Part of the precipitation is lost through evaporation, with interception of the plants and within small depressions P • How to determine that amount? ET • Model of Potential Evapotranspiration (PET)
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PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Evapotranspiration
Factors affecting Evaporation Factors affecting transpiration • Water temperature • A function of • Air temperature above water layer • plant density • Absolute humidity of air above • plant size water surface • limited by soil water. • Wind – keeps absolute humidity • Wilting point = surface tension of soil- low water interface > Osmotic pressure. • Solar radiation
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. Infiltration
• Part of the precipitation that reaches ground can now start with two processes: surface runoff and infiltration into ground
P • The process in which water is absorbed by soil during a rainfall ET • 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. G R
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Author Function Legend Infiltration f 푡 - infiltration capacity during time [cm/s] −γ 푓0- initial inflitration capacity [cm/s] Horton f 푡 = 푓푓 + 푓0 − 푓푓 푒 푓푓- final infiltration capacity [cm/s] • Physically based models γ - constant depending on the soil type −훼 • Water movement in soils Kostiakov f 푡 = 푓0푡 α - constant depending on the soil conditions in a simplified manner 푓 - inflitration cpacity time t=qmin [cm/s] Dvorak – 1 f 푡 = 푓 + 푓 − 푓 푡−푏 t - time [s] • Focusing especially on Mezencev 0 1 푓 humidity front level b - constant c - factor variable from 0.25 to 0.8 • Depending on physical 푛 Holtan f 푡 = 푓푓 + 푐푤 퐼푀퐷 − 퐹 w - Holtan equation flow factor parameters n - experimental constant, approximately = 1.4
s - sorptivity [cms-0.5] 1 Philip f 푡 = 푠푡−0.5 + 퐴 A - gravity component depending on 2 hydraulic conductivity at saturation [cm/s]
a - constant
Dooge f 푡 = 푎 퐹푚푎푥 − 퐹푡 Fmax - maximal retetion capacity Ft - water quantity retained on soil at time t
푘푠 - hydraulic conductivity at saturation [mm/h] ℎ0 − ℎ푓 ℎ0 - surface pressure load [mm] Green&Ampt f 푡 = 푘푠 1 + 푧푓 푡 ℎ푓 - pressure load at the humidity front [mm] Source -Musy, 2001 푧푓 - humidity front depths [mm]
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 Rainfall −푡ൗ f, i 푓푐푎푝푎푐𝑖푡푦 = 푓푐 + 푓0 − 푓푐 푒 퐾
fcapacity = maximum infiltration capacity of the soil f0 = initial infiltration capacity Infiltration curve fc = final (constant) infiltration capacity t = elapsed time from start of rainfall K = decay time constant The actual infiltration rate must be equal to the smaller of the rainfall intensity i(t) and the infiltration capacity fcapac
푓 = 푓푐푎푝푎푐𝑖푡푦 for 𝑖 > 푓푐푎푝푎푐𝑖푡푦 time 푓 = 𝑖 for 𝑖 ≤ 푓푐푎푝푎푐𝑖푡푦 f = actual infiltration rate (mm/hr or inches/hr) i = rainfall intensity (mm/hr or inches/hr).
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) Green-Ampt model idealization of wetting front penetration into a soil profile Actual infiltration Green & Ampt infiltration 푀푆 0 Moisture Content 휗 0 Moisture Content 휗 푓 = 퐾 1 + 퐾 Saturated Zone 휗푆
M = moisture deficit 푀 = 휗푆 − 휗퐼 Transmission Saturated Saturated 퐿
S = suction head Zone Zone Length Depth K = Hydraulic Conductivity Depth Wetting Front 휗 = Initial Moisture Content 퐼 Wetting 휗푆 = Saturated Moisture Content Zone Wetting Front 휗퐼 푀
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Effective precipitation
• What is the amount of the precipitation, after all losses that will be part of surface runoff? • SCS CN method P ET
A Peff Qef Peff x A G R t
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 • The CN (Curve Number) method 푷 풕 − 푰 ퟐ 푸(푷풆풇풇) = 풂 does not consider intensity and 푷 풕 + 푺 − 푰풂 duration of rainfall, only total rainfall 푄 − depth of runoff – is equal Peff volume 푃 − depth of rainfall 퐼 − 푎 initial abstraction 25400 푆 − potential storage 푆 = − 254 푚푚 CN − curve number for the day ≤ 100 퐶푁
The CN can be obtained from tables – soil type and moisture correlations
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Groundwater flow
• Movement of water between unsaturated and saturated zone • Water available to plants P ET
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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. 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. Darcy’s Law
• Henri Darcy established Elevation B: empirically that the energy lost Flow distance (l) Water table = ∆h in water flowing through a Elevation A: Y [m] above permeable formation is Water table see level = proportional to the length of the A sediment column ∆L. X [m] above see level Water Table B • The constant of proportionality DARCY’s LAW K is called the hydraulic 풉 = 푿 − 풀 2 풉 A [m ] conductivity. The Darcy Velocity 푸 = 푨 푲 풍 VD: K = Permeability VD = – K (∆h/∆L) and since Q = VD A (hydraulic conductivity) (where A = total area) l = flow distance h = vertical drop Q = – KA (dh/dL) A = cross sectional area of flow
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. DARCY’s LAW 풉 Range of values of K 푸 = 푨 푲 풍
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
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 Sediment0 Porosity (%) Permeability number of fractures (most often Gravel 25 to 40 Excellent very low, <5%) Sand (clean) 30 to 50 Good to Excellent • Permeability is not proportional to Silt 35 to 50 Moderate porosity. Clay 35 to 80 Poor Glacial till 10 to 20 Poor to Moderate PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Runoff
• Total flow in a stream on measuring gage • Groundwater contribution to a stream is baseflow P ET
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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. Runoff pathways • Groundwater flow • Subsurface flow (interflow) • Overland flow
Formation process of surface runoff • 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.
푄푝 = 푘 퐶 𝑖 퐴 k = unit conversion factor (1.008 for English unit; 0.27 for metric unit) 3 3 Qp = peak discharge (ft /s or m /s) i = rainfall intensity (in/hr or mm/hr) C= runoff coefficient is a 2 A = drainage area (acres or km ) dimensionless coefficient relating i = average intensity of rainfall corresponding to the amount of runoff to the the duration of time-of-concentration 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 t2
TC 100% % % Area c = Rational method runoff coefficient G = Constant. FAA: G=1.8, Kirpich: G=0.0078, Kerby: G=0.8268 k = Kirpich adjustment factor time L = Longest watercourse length in the watershed [m] r = Kerby retardance roughness coefficient. t1 S = Average slope of the watercourse [m/m]. B t = Time of concentration, [min]. V = Average velocity in watercourse, m/min. V=L/t.
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Runoff pathways • Groundwater flow • Subsurface flow (interflow) • Overland flow
Formation process of surface runoff • Surface runoff • overland flow (sheet flow) • shallow concentrated flow • open channel flow
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Open channel flow
General Flow Equation 푸 = 풗푨
A Area of the cross-section (m2) v Avg. velocity of flow at a cross-section (m/s) Flow rate (m3/s)
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 Very sensitive to n Open channel flow example - River Avon, City of Bristol 1 2/3 1/2 1 2/3 1/2 푉 = 푅ℎ 푆0 푄 = 푉퐴 푄 = 퐴푅 푆 푛 푛 ℎ 0 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) Image Credits: http://www.geograph.org.uk/photo/5898965 Q = volume flow (m3/s) A = cross-sectional area of flow (m2)
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Manning roughness coefficient, n
Lined Canals n Natural Channels n Cement plaster 0.011 Gravel beds, straight 0.025 Untreated gunite 0.016 Gravel beds plus large boulders 0.040 Wood, planed 0.012 Earth, straight, with some grass 0.026 Wood, unplanned 0.013 Earth, winding, no vegetation 0.030 Concrete, troweled 0.012 Earth, winding with vegetation 0.050
Concrete, wood forms, unfinished 0.015 n = f (surface roughness, channel irregularity, stage…) Rubble in cement 0.020 There are numerous factors that affect n-values, including: Asphalt, smooth 0.013 ▪ Surface roughness ▪ Seasonal change Asphalt, rough 0.016 ▪ 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. Movement of water and land mass
• Erosion and land mass movement also present in watershed • Production and transport of sediment P ET
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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: • INRA Model • Erosion Potential (Gavrilović) Method • SCALES Model • Factorial Scouring Model (FSM) • Fournier • Erosion hazard units (EHU) • Water Erossion Prediction Model (WEPP) • Soil Loss Estimation Model for Southern Africa (SLEMSA) • Soil and Water Assessment Tool (SWAT) • CORINE erosion risk maps • Morgan Morgan Finney (MMF) • Coleman and Scatena scoring model • Annualized Agricultural Non-Point (CSSM) Source Pollution (AGNPS) • Fleming and Kadhimi scoring model • Modified Universal Soil Loss Equation (FKSM) (MUSLE) • Wallingford scoring model (WSM) • Universal Soil Loss Equation (USLE) • Revised Universal Soil Loss Equation (RUSLE) • RIVM Model
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:
ퟎ.ퟓퟔ 풔풆풅 = ퟏퟏ. ퟖ 푸풔풖풓풇풒풑풆풂풌풂풓풆풂풉풓풖 푲푼푺푳푬푪푼푺푳푬푷푼푺푳푬푳푺푼푺푳푬푪푭푹푮 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) 2 3 KUSLE = USLE soil erodibility factor = 0.013 metric ton m hr/(m -metric ton cm) CUSLE = USLE cover and management factor The main difference compared to the USLE is P = USLE support practice factor USLE the replacement of the rainfall factor with a LSUSLE = USLE topographic factor CFRG = coarse fragment factor direct estimate of surface runoff and peak runoff rate
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. 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 NONPOINT SOURCES waters, groundwater, sediments, and ultimately in drinking water Rural homes • Two primary source categories: Urban streets Cropland (1) point-source pollution Animal feedlot (2) non-point-source (diffuse) Suburban POINT pollution developm SOURC Factory ent ES Wastewat er treatment plant
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Sources of diffuse water pollutants
• Agriculture NONPOINT SOURCES • Pathogens
• Sediment Rural homes • Pesticides • Atmosphere Urban streets Cropland Animal feedlot
Suburban POINT developm SOURC Factory ent ES Wastewat er treatment plant
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 crop Poor crop Established crop Seedbed application Soil Heavy soil Light soil Poor drainage Good drainage Time of application At the beginning of At the end of (fertilizer) the main growing growing season or period or during out of season active crop growth Climate Low rainfall High or irregularly distributed rainfall
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018. Nutrients – sources and pathways
In stream Uptake and release Deposition Transport
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. Modeling contaminants
SWAT Modeling methods for water quality Sediment routing Controlled by deposition and degradation processes Max. amount transported - Function of maximum flow velocity Nutrient routing METHOD: In stream kinetics with QUALE 2 method (Brown and Barnwell, 1986) Nutrients dissolved in the stream – transported with the water Nutrients adsorbed to the sediment – transported/ deposited within channel Channel pesticide routing Sediment transformation in dissolved and sediment- attached METHOD: First-order decay relationship Modeled 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).
PESFOR-W Training School - Porto, Portugal – 23.-26. October 2018.