Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal

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Groundwater nutrient loadsThe groundwater nutrient load to the stream is obtained by multiplying the flow fromeach groundwater box by the groundwater nutrient concentration. The monthlygroundwater nutrient load is thus calculated as follows:dm∑DG = 0.1* AT(C1G1+ C2G2)(11)mgt=1tdm∑gt=1whereC1 g = nutrient concentration in groundwater box 1 [mg/l]C2 g = nutrient concentration in groundwater box 2 [mg/l]AT = watershed area [ha]3.3 AVAILABLE OBSERVATION DATA USED IN THE STUDYg3.3.1 Climate dataClimate data (daily precipitation and mean air temperature) for the years 1980 to 2000were taken from the BALTEX Hydrological Data Centre data base administrated bySMHI. The value of daily temperature and precipitation is a spatial and temporal meanof several measuring points in the basin and several times of measurement during theday (Danielsson, 2005).3.3.2 Streamflow and nutrient load dataThe reported data consist of monthly means of streamflow, total nitrogen load and totalphosphorus load from 19702000 (Wulff and Rahm, 1990; Stålnacke 1996) with somedata gaps during the 90’s. In figure 5 the reported streamflow and the reported loads ofnitrogen and phosphorus from the Daugava are displayed. Data from 19701990 werecompiled by Stålnacke (1996) with help from data obtained from the LatvianHydrometeorological Agency in Riga. Gaps in the data series were filled in by the useof statistical interpolation and extrapolation methods. Different sampling sites wereused and it is not clear where the sampling sites are located, but they are probablysituated a considerable distance from the mouth of the river. Since the areas of differentland uses in the basin have been calculated from the mouth of the river this means thatthe drainage area used as model input is overestimated with respect to the drainage areaof the sample stations. Also, the impact of Riga is not included in reported data, sinceRiga is situated at the mouth of the Daugava. Considering the data from the 90’s, thereis little information on how the data series were compiled and where the sample stationis located.12
10^6 m3ton/monthton/month1000080006000400020000Jan70Jan7125000.0020000.0015000.0010000.005000.000.001000.00800.00600.00400.00200.000.00Jan70Jan71Jan70Jan71Jan72Jan73a) StreamflowJan72Jan73Jan74Jan75Jan76Jan77Jan78Jan79Jan80Jan81Jan82Jan83Jan84Jan85Jan86b) Nitrogen loadJan72Jan73Jan74Jan75Jan76Jan77Jan78Jan79Jan80Jan81Jan82Jan83Jan84Jan85Jan86c) Phosphorus loadJan74Jan75Jan76Jan77Jan78Jan79Jan80Jan81Jan82Jan83Jan84Jan85Jan86Jan87Jan88Jan89Jan90Jan87Jan88Jan89Jan90Jan91Jan92Jan93Jan94Jan95Jan96Jan97Jan98Jan99Jan00Jan87Jan88Jan89Jan90Jan91Jan92Jan93Jan94Jan95Jan96Jan97Jan98Jan99Jan00Jan91Jan92Jan93Jan94Jan95Jan96Jan97Jan98Jan99Jan00Figure 5. Reported monthly streamflow (a) and load of total nitrogen (b)and phosphorus (c) from the Daugava River for the years 19702000.3.4 CALIBRATION AND VALIDATIONThe model was applied to the Daugava drainage basin with the input data and parametervalues presented in Appendix A. In the appendix it is also described which parameterswere calibrated.Climate data were not available for the 1970’s, which is why only the 1980’s and1990’s could be used for calibration and validation. Seven years during the 1990’s(19931999) were used for calibration. They were chosen because they were the mostrecent years and the desire was to achieve a calibration as close to the present situationas possible. As a first step calibration was done for the hydrological part of the model.The evapotranspiration cover coefficients (CV t ), curve numbers (CN2 k ) and coefficientsfor groundwater flow (r1, r2 and gr) were used as calibration parameters. In order toobtain the best fit several aspects were taken into consideration. It was a trade offbetween obtaining an average value over the seven years of the predicted streamflow asclose to the observed average value as possible, minimising the average percentageerror and reaching the observed top flows. The process was iterative and since there isno builtin calibration procedure in CatchmentSim the work had to be done manually.13
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 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 40 and 41: wherea t = rainfall erosivity coeff
Page 42 and 43: Appendix F. Regression lines of rep

Nutrient Transport Modelling in the Daugava River Basin - DiVA Portal

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