etude de la qualite des eaux d'un hydrosysteme fluvial ... - LTHE

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The friction factor is calculated from Chezy coefficient:f c = g/C 2where g: gravity force (m/s 2 )C: Chezy coefficient (m 1/2 /s)In most modelling studies, the critical shear stress for deposition is assumed uniform andconstant. Since the experiment on shear stress determination was not carried out, thepublished values relating to critical shear stress in mud bottom were referenced and declaredbetween 0.035 and 0.2 N/m 2 (Winterwerp, 1991).+ ErosionThe erodability of cohesive sediments is driven both by shear and by the rheologicalproperties of the bottom. From the reality of the Nhue river, it is assumed that the availabilityof deposited mud for erosion is always fulfilled. A similar approach has been tested byMulder and Udink (1991) in the case of the Scheldt river (Belgium). The erosion rate ofsediment organic material is calculated according to the formula of Partheniades (1962):τb PE0 (1 − ) SOM, sedif τ b >=τ ce else 0 (2.2.21)τ Acewhere E 0 : erosion coefficient (kg/m 2 /s)τ b : local bed shear (N/m 2 );τ ce : critical shear stress for erosion (N/m 2 )S OM,sed : organic material content in sediment (kg/kg)The erosion coefficient (E 0 ) depends on the physico-chemical characteristics of bottomsediments. Because these properties are poorly know, this parameter can simply be consideredas a calibration parameter of the mud transport model. In this case, again, published data werecollected and declared; 10 -4 - 10 -5 kg/m 2 /s (Mulder and Udink, 1991).110
The critical shear stress for erosion is a function of the degree of compaction of the sediments.This is again an extremely complex parameter to determine. In this case, we selected a valuebetween 0.02 and 0.4 N/m 2 (Mulder and Udink, 1991). It is needed to note that theresuspension of sediment particles only occurs when τ b >=τ ce and from our experience in theNhue river the resuspension rarely occurs.Based on the fact that bacteria tend to associate with suspended particulate material, a portionof bacteria biomass equivalent to the ratio of bacterial biomass/SPM content is modelled todeposit in conjunction with sedimentation of suspended material. Though bacterialsedimentation is associated with sedimentation of SPM (inorganic origin), the sedimentationof particulate organic matter (POM) may not be as fast as SPM because of great difference indensity. Since the model simulates the dynamics of bacteria and POM, different settling ratefor POM and SPM would be appropriate.2.4.2.2.4. Adsorption/Desorption (PO 4 )Adsorption is defined as any type of binding of phosphate on particulate matter. Desorption ofphosphate is release of phosphate previously bound on particulate matter. Equilibriumexpression of the adsorption/desorption process is as follow− k( T −T° )( S+ S) KβHPO4H 2PO4ads SPMads0 e ( −ads,T−61eSPS1)(2.2.22)where K ad : first order equilibrium of adsorption/desorption of PO 4S P : adsorbed PO 4 in particulate phase and can be released easily to dissolved phase butis not readily available for biological uptake and chemical equilibriumIn aerobic condition the K ad is reported as 35 by Garnier et al (2000a). It is necessary tomention that S P is different from particulate phosphorus that includes particulate organicphosphorus and particulate inorganic phosphorus suspended in water column. The sink of S Pis by sedimentation of SPM and desorption to PO 4 . The adsorption of PO 4 is rapid as initial111
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THESISFor obtaining the doctorate d
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3. utilisation de ce modèle pour
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L’ensemble de ces indices permet
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2. Modélisation du système fluvia
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3. Caractéristiques principales de
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ForewordsThis thesis pursues an env
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Principal contentsIntroduction 1Pre
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framework for which it was develope
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PART 1: PRESENTATION OF THE STUDY5
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1. The Nhue-To Lich river basins1.1
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3.77 m for low and high irrigation,
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1.2.2. RainfallFigure 1.1.4: Monthl
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Over the whole year, the monthly av
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Figure 1.1.15: Pie chart of land us
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2. Data base constructionIn order t
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2.2. Organization of the field surv
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confluence point. The other points
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In summary, the frequency of the ex
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Point Time Level Discharge Cross-se
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conducted independently from the sc
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Figure 1.2.7: DO in on-boat surveyF
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Figure 1.2.9 presents the photos of
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degradable organic fraction in tota
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natural products chemistry led by P
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The analysis of chlorophyll-a is ca
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small comparison between DOC, BOD m
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3. Hydrology of the Nhue-To Lich ri
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Figure 1.3.3: Gate structure at the
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The rating curve at Cau Den was als
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counted here is constantly distribu
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4. Water quality of the Nhue-To-Lic
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Figure 1.4.5: DO extracted from mon
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the contrary, the low correlation o
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Figure 1.4.13: PCA of the upstream
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anthropogenic impact is short at th
Page 79 and 80: In conclusion, the seasonal variati
Page 81 and 82: NO3 in nitrification process requir
Page 83 and 84: PART 2: MODELLING OF THE NHUE-TOLIC
Page 85 and 86: IntroductionOne objective of this t
Page 87 and 88: definition of the system identifies
Page 89 and 90: Y = [(Σ((x c - x m ) 2 /x m,a )/n]
Page 91 and 92: 3. The validation criteria are form
Page 93 and 94: 1.2.2. Hydrodynamics and hydraulics
Page 95 and 96: AQUASIM's second task is to perform
Page 97 and 98: QUAL2 was specifically designed to
Page 99 and 100: UK; Wallingford Software 1994); 8 =
Page 101 and 102: system will be declared in the next
Page 103 and 104: The performance of parameter estima
Page 105 and 106: Based on these 3 factors, we have c
Page 107 and 108: The lengths of the first, the secon
Page 109 and 110: Figure 2.2.2: Rear Thuy Phuong dam
Page 111 and 112: 2.3.3. Biochemical conceptual schem
Page 113 and 114: 1973; Yen, 1979; French, 1985). The
Page 115 and 116: + Heterotrophic growth on dissolved
Page 117 and 118: The loss of heterotrophic biomass i
Page 119 and 120: O 2 /l)P/l)S NH4 : concentration of
Page 121 and 122: In contrast, the Nhue river is ofte
Page 123 and 124: 2.4.2.1.4. Estimation of the kineti
Page 125 and 126: In fresh water environment, the equ
Page 127 and 128: + NH 4 exchangeIn this equation, th
Page 129: τ cd : critical shear stress for d
Page 133 and 134: 2.4.2.2.6. Precipitation/dissolutio
Page 135 and 136: The table 2.2.9 represents complete
Page 137 and 138: 3.2. Initial and boundary condition
Page 139 and 140: N1TLSpecies Prior simulation After
Page 141 and 142: 3.3. Simulation prior to calibratio
Page 143 and 144: adsorption in our river. The decrea
Page 145 and 146: and an intermediate class 2 with
Page 147 and 148: 3. The half-saturation coefficients
Page 149 and 150: negligible factor in the polluted a
Page 151 and 152: 3.5. Results of the post-calibratio
Page 153 and 154: conceptual scheme and in providing
Page 155 and 156: case of inundation. We suppose that
Page 157 and 158: the inconsistence data employed in
Page 159 and 160: 4. Simulation of the transient stat
Page 161 and 162: water discharge can dilute the diss
Page 163 and 164: this modelling period with previous
Page 165 and 166: 4.4.1.3. Estimation of accumulative
Page 167 and 168: 4.4.2.2. Boundary conditions for un
Page 169 and 170: Figure 2.4.19: Initial condition of
Page 171 and 172: The diurnal variation is another tr
Page 173 and 174: Figure 2.4.29: Simulated and measur
Page 175 and 176: August 1 st to 4 th 2003. Of which
Page 177 and 178: The wind speed was predicted from t
Page 179 and 180: occurrence is regular whenever rain
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Figure 2.4.47: Boundary condition o
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Figure 2.4.55: Simulated and measur
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Figure 2.4.59: Turbidity at NT1 in
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PART 3: DISCUSSION167
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IntroductionIn the previous parts,
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Figure 3.1.1: Average chlorophyll-a
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In conclusion, with high nutrient l
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Dissolved oxygen (g O 2 /m 2 /d) NH
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- DO balanceFigure 3.1.9: Dissolved
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- NH 4 balanceFigure 3.1.11: NH 4 b
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Figure 3.1.14: NH 4 balance in summ
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Figure 3.1.15: Exponential relation
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2. Investigations toward restoratio
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Figure 3.2.3: Simulation based on d
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The distance of recovery is hardly
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upstream inflow. It also implies th
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So far, the wastewater of the Hanoi
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The simulation results of two varia
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Figure 3.2.17: DO at NT2 in differe
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Figure 3.2.21: Evolution of DO at d
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As shown in simulation results, the
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Conclusion and perspectivesConclusi
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processes which were not measured.
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1. Annex 1: Experimental protocols
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PO 4P totalRange Method Standardsol
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- Analytical methods+ BOD: Water sa
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MgClSO 4HCO 3TraceelementsRange Met
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2. Annex 2: Estimation of organic m
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Ratios between heterotrophic bacter
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- To assess the individual local pa
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δmabsj=1n∑n i=1sijParameter rank
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The above definition has a simple i
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4. Annex 4: Mathematical formulas i
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⎛∧ ⎜j = ⎜QC⎜⎝iQ ⎞∂C
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6. Annex 6: Stoichiometric coeffici
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Subs. ValueUnitaerobic sediment exc
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kwind⎛= ⎜⎝ 3.6e1−1 225 10
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DO evolution in Bell Jar experiment
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Firstly of all, NH 4 and DO behave
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Results of Bell Jar experiment at T
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As clearly observed in the figure a
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10. Annex 10: Parameter estimation
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and parameter estimation. It is exp
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First of all, an experimental layou
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ate of phytoplankton also ranks low
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ReferencesAalderink R.H., Klaver N.
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Brown L.C. and Barnwell T.O. (1987)
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Henze M., Grady C.P.L., Gujer W., M
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Liss, P.S. and Slater, P.G. (1974)
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Prieur N. (2001) Dynamique des cont
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Smith, V. H., Tilman G. D., and Nek
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Zonneveld C. (1998) A cell-based mo
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