Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal

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wherea t = rainfall erosivity coefficientR t = rainfall on day tThe rainfall erosivity coefficient varies with season and geographic location.In order to determine the transport of sediments in each month, a transport factor isdefined as:d j∑TR j= Q tt=15 / 3(D4)The sediment produced in month j will be allocated to months j, j+1, … 12 in proportionto the transport capacity of each month. The total transport capacity for months j,j+1, … 12 is proportional to the sum of the transport factors during these months,defined as B j .B∑= 12 jTR hh=j(D5)For each month, the fraction of available sediment X j which contributes to Y m , isTR m /B j . The total monthly yield is the sum of all contributions from preceding months:Ym= TRm∑mj=1( X / B )(D6)jjAppendix E. Determination of urban runoff nutrientloadsUrban surfaces are assumed to be impermeable. Nutrients accumulate on urban surfacesover time and are washed off by runoff events. The accumulation rate during dryperiods is:dNdtk= n − β ⋅ N(E1)kkwhereN k (t)= accumulated nutrient load on land use k on day t [kg/ha]n k = constant accumulation rate [kg/(ha*day)] = depletion rate constant [day 1 ]By solving equation E1 we obtain:Nk(k 0−βt−βtt)= N e + ( n / β )(1 − e )(E2)k34
whereN k0 = N k (0)With increasing time, equation E2 approaches an asymptotic value as the depletion rateapproaches the accumulation rate:N = lim N ( t)= nk , maxk kt→∞/ β(E3)Assuming that N k (t) reaches 90 % of its maximum value in 20 days, the equations canbe solved for . The result is = 0.12, which is the value that is used here.Equation E2 can be written for a time interval of one day, which is the form that is usedby the GWLF model:N−0.12= N e + ( n / 0.12)(1 ek , t+ 1 ktk−−0.12)(E4)By adding a negative term to the right hand side of this equation, the effect of wash offis included:N−0.12−0.12k , t+ 1= Nkte+ ( nk/ 0.12)(1 − e ) −Wkt(E5)whereW kt = runoff load from land use k on day t [kg/ha]The runoff nutrient load at a wash off event is a function of the amount of accumulatednutrients at the time and the runoff flow:Wkt.12= w [ N e + ( n / 0.12)(1 − ektkt−0 −0.12k)](E6)where−1.81Q w ktkt= 1 − e(E7)Equation E7 is based on the assumption that 1.27 cm of runoff will wash off 90 % ofaccumulated pollutants.Monthly runoff loads of urban nutrients are thus given by:SUm=∑∑( Wkt⋅ARk)kdmt=1(E8)35
Page 1 and 2: UPTEC W05 009Examensarbete 20 pFebr
Page 3 and 4: Nyckelord: avrinning, näringsämne
Page 6 and 7: APPENDIX C. DETERMINATION OF POTENT
Page 8 and 9: simulation system CatchmentSim. The
Page 10 and 11: Figure 1. The hydrological part of
Page 12 and 13: TemperaturePrecipitation20.00120deg
Page 14 and 15: 3.2 MODEL DESCRIPTION3.2.1 An overv
Page 16 and 17: Groundwater discharge to the river
Page 18 and 19: Groundwater nutrient loadsThe groun
Page 20 and 21: There is therefore no guarantee tha
Page 22 and 23: a) Streamflow, calibration periodb)
Page 24 and 25: 4.2 IMPACT OF THE CURVE NUMBER ON N
Page 26 and 27: the chosen value is a very rough ap
Page 28 and 29: all cultivated land will have winte
Page 30 and 31: HELCOM, 2004a. 30 years of protecti
Page 32 and 33: Appendix A. Input data and paramete
Page 34 and 35: Description of parameter/input Name
Page 36 and 37: Description of parameter/input Name
Page 38 and 39: moisture.Figure B1. Selection of cu
Page 42 and 43: Appendix F. Regression lines of rep

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