Lecture #1. Introduction into unsaturated zone (UZ) hydrology. Interdependency of terrestrial water resources

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1 Lecture #1. Introduction into unaturated zone (UZ) hydrology 1.1. Migration procee imulation in UZ The earth layer that contain three phae of matter (olid, liquid and ga) ha been termed the unaturated zone (zone of aeration or vadoe zone) The UZ i typically defined to extend from land urface to the underlying ater tale or aturated zone ithin porou media. The UZ ha a ignificant influence migration of both ater and chemical. Variable of tate that affect the unaturated zone include preure, temperature and concentration. Soil phenomena uch a capillary flo, adorption, chemical interaction, matric potential, root uptake etc. are dependent on tate variable. An UZ ytem i governed by thermodynamic principle, and, in mot intance, follo the la of phyical chemitry. Interdependency of terretrial ater reource Pr Ev Pm Precipitation, Irrigation Surface ater Fertilizer, Salt Evaporation, Tranpiration Root uptake Contaminant Unaturated Zone Surface ater zone R Pm Groundater zone Pr ET Soil ater zone (unaturated) Saturated zone Pr - precipitation, Ev -evaporation, Pm - pumping, ET - evapotranpiration, R - recharge Model i a implified verion of the real (e.g. oil) ytem that approximately imulate the excitation-repone relation of the latter. Objective of imulation: Simulation of the procee improve our undertanding of the real ytem behavior. Simulation of the procee in the unaturated zone improve the characterization of infiltration and olute flux. 1

2 1.2. The oil profile Soil formation reult in the natural development of layer ithin a profile. Each of thee layer i compoed of tructural unit coniting of variou fraction of and, ilt, clay and organic matter. When formed in place by pedogenic procee, the layer i called a horizon Repreentation of a complete oil profile (left) ith horizon (right) decription (Hillel, 1982) 1.3. Soil a a multiphae and multi-component ytem Porou medium (PM) olid matrix + void pace Phae - there i an interface beteen them (olid, ater, air, oil, etc) Mineral matter Water Schematic compoition of a oil Air Organic matter Component - there i no interface beteen them. in olid phae: variou mineral; in olution: ion, ion complexe; in air: different gae 2

3 1.4. Volume and ma relationhip of oil contituent indexe: a air, ater, olid, t total REV (Repreentative Elementary Volume) volume the minimal volume of ample needed to obtain a conitent value of meaured parameter Denity of olid Ma of olid in REV M Volume of olid in REV V Dry bulk denity Ma of olid in REV M M b Volume of REV Vt Va + V + V Poroity Volume of void in REV Va + V b n, n Volume of REV Va + V + V Ma ater content Ma of ater in REV M θ m Ma of olid in REV M Volume ater content Volume of ater in REV V θ m b θ ; 0 θ n, θ, Volume of oil ample in REV Vt Water aturation Volume of ater in REV V S ; 0 S 1 θ Sn Volume of void in REV V 1.5. Soil texture, oil clae and oil tructure The texture of oil i determined by the repective proportion of fraction of the and, ilt and clay ized particle. p Conventional cheme for the claification of oil fraction: US Dep. of Agriculture (USDA), Int. Soil Sci. Society (ISSS) US Public Road Admin. (USPRA), Britih Standard Int. (BSI), Maachuett Int. of Technology (MIT), German Standard (DIN) Comparative ize of and, ilt and clay particle The method ued to ort oil eparate i called particle ize analyi or mechanical analyi. Methodologie ued: pipetting, hydrometer, centrifugation, elutriation and ieving. 3

4 The texture cla of a oil i determined by the proportion of the three ize fraction: and, ilt and clay Textural triangle, hoing the percentage of clay (belo mm), ilt ( mm) and and ( mm) in the conventional oil textural clae Particle ize ditribution curve for variou type of oil material (chematic) Soil tructure decribe ho the variou ize fraction are grouped together into table aggregate: Depiction of oil tructure, data from USDA 4

5 Structure of granular oil Packing of polydipere particle Model of packing of equal phere: (a) imple cubic (n0.476) (hypothetical) (b) cubical tetrahedral ((n0.395), (c) tetragonal phenoidal (n0.302) (d) pyramidal (n0.26), and (e) tetrahedral (n0.26) (Dereieicz, Form of ater in oil Range of ater aturation: (a) (b) (c) (d) Solid Water Air Water and air aturation tate: (a) Pendular aturation; (b) Pendular ring beteen to phere (c) Funicular aturation; (d) Inular air aturation 1) Pendular - lo aturation, the ater ring are uually iolated and do not form a continuou ater phae. A very thin film of ater remain on the olid urface, practically no preure can be tranmitted through it from one ring to another. 2) Funicular - continuou ater phae i formed and flo of ater i poible. Air phae i continuou too. 3) Inular - cloe to full aturation. A bubble of air can move only if preure difference, ufficient to queeze through a capillary ize retriction. 4) Irreducible (adorbed tage) - very lo aturation, adheive ater left hich i ometime called hygrocopic moiture. 5

6 1.6. The concept of field capacity and ilting point Field capacity i the amount of ater held in oil after exce ater ha drained aay and the rate of donard movement ha materially decreaed, hich uually take place ithin 2-3 day after rain or irrigation in perviou oil of uniform texture and tructure (Veihmeier and Hendricon, 1952). The changing moiture profile in medium-textured oil during reditribution folloing irrigation The monotonic decreae of oil ater content ith time in the initially etted zone of a clayey and a andy oil during reditribution ( field capacity i ater content remaining in oil after 2 day) Wilting point i the root zone oil etne at hich the ilted plant can no longer recover turgidity even hen placed in a aturated atmophere for 12 h (Briggz and Shantz, 1912) The concept of oil-ater availability to plant The bucket model : a implitic repreentation of oil moiture availability beteen field capacity and ilting point Three claical hypothee regarding the availability of oil ater to plant: (a) equal availability from field capacity to ilting point, (b) equal availability from field capacity to a critical moiture beyond hich availability decreae, and (c) availability decreae gradually a ater content decreae Modern concept: the amount and rate of ater uptake depend on the ever varying ability of root ytem to aborb ater from the oil in hich it i embedded, a ell a on the capacity of the oil to upply the root at a rate ufficient tranpiration requirement. 6

7 Volumetric (%) oil ater content at field capacity, ilting point and available for variou oil texture: Soil texture Field capacity (%) Wilting point (%) Available ater content (%) Sand Loamy Sand Sandy Loam Loam Silt Loam Silty Clay Loam Clay loam Sandy Clay Loam Sandy Clay Silty Clay Clay Ratlif et al. 1983, SSSAJ, 47:

8 1.8. Meauring oil ater content. Sampling and drying Drying ample of oil in an oven at 105 o C for 24 h (et eigth) - (dry eight) θ m dry eight Advantage: direct meaurement of ater content. Diadvantage: ome clay may till contain appreciable amount of aborbed ater even at 105 o C, ome organic matter may oxidize and decompoe at thi temperature. Extraction of ample may diturb obervation and ditort the reult. Electrical reitance Meauring electrical reitance of a porou block (uually made from gypum, porou fibergla or nylon), hich i in equilibrium ith the matric olution. Calibration againt oil ater content i needed. Advantage: Connected to a recorder allo to obtain a continuou indication of ater content Diadvantage: effect of hyterei, time-lag, effect of alinity and temperature. Neutron cattering Fat neutron (alpha particle) are emitted by a Ra-Be ource into oil, lo don by looing their energy. Slo neutron are counted by detector. A linear relation beteen count rate and ater content i ued. Advantage: allo le laboriou; more rapid, nondetructive (after intallation) and periodically repeatable meaurement. Diadvantage: high initial cot of the intrument, lo degree of patial correlation, difficulty of meauring ater content in the oil urface zone, health hazard aociated ith expoure to neutron and radiation. 8

9 Gamma-Ray adorption. A 137 C emitting gamma radiation detected by a cintillation counter. An exponential relation beteen count rate and ater content i ued to find ater content. The gamma-ray adorption method ued motly in lab, here dimenion and denity of oil ample, a ell a the ambient temperature, can be controlled. Advantage: high degree of patial reolution (e.g. 2 mm). Diadvantage: health hazard aociated ith expoure to radiation. Time-Domain Reflectometry Device meaure time beteen ending pule ignal and receiving the reflected ignal. Velocity propagation of electromagnetic ave and the dielectric contant of media are found. A polynomial relation beteen the dielectric contant and ater content i ued to find ater content. v c ε v 2L t ε r r ( ct 2L) 2 θ ε r ε r ε r 9

10 Problem 1. A et oil ample from a field ha ater content on a ma bai of 0.1 g/g a. If you require ufficient oil to pack a 100,000 cm 3 column to a dry bulk denity of 1.4 g/cm3, hat ma of moit oil mut you collect from the field? b. Calculate the poroity of thi ample, auming a oil particle denity of 2.65 g cm -3. c. Ho much ater mut be added (cm 3 ) to bring thi oil ample to full aturation. 2. A ample of moit oil having a et ma of 1000 g and a volume of 640 cm 3 a dried in the oven and found to have a dry ma of 800 g. Auming the typical value of mineral denity of 2.65g cm -3, calculate a. the dry bulk denity b. the poroity c. the ater content by ma, d. the volumetric ater content, e. the degree of aturation, S 3. The ater content of a ample of moit oil i determined to be 0.05 g/g on a ma bai (gravimetric ater content). a. If a ample of 60 g i taken, ho much oven-dry oil i preent? b. Ho much ater (cm 3 ) i preent in thi 60 g oil ample. c. If thi ample of 60 g ha a bulk oil volume of 40 cm3, and the oil particle denity i 2.60 g/cm, compute the oil poroity of thi ample. d. Ho much ater mut be added to bring the ample to a ater content of 0.2 cm3/cm3? e. What i the air-filled poroity of thi oil ample ith a gravimetric ater content of 0.20 g/g? 10