Antti Taskinen

Generation of two-dimensionally variable saturated hydraulic conductivity fields: Model theory, verification and computer program

The theory for the generation method of spatially variable Ks fields, using a set of scaling factors of log-normally distributed random field with two-dimensional correlation structure, is compiled from different sources. It is developed further by derivation of computational formulas of model parameters for a general case. The user of the method needs to define the mean, coefficient of variation and correlation length of the Ks fields. Both isotropic and anisotropic fields can be generated. The method and the computer program, which is provided for readers, are verified by analyzing example generations carried out by set of different parameter values. Since the materializations of the set values in generated fields were found satisfactorily accurate and their distributions cohered the model structure, the method and the computer program can be considered a useful and reliable tool for simulation of spatially variable hydraulic conductivity fields. However, the way of the method treating the covariance structure of the random vector limits the field size or the number of nodes where the Ks values are to be generated.

Phosphorus and nitrogen fluxes carried by 21 Finnish agricultural rivers in 1985–2006

The Finnish Agri-Environmental Programme aims to reduce nutrient load to waters. Using national monitoring data, we estimated the agricultural load (incl. natural background) of total phosphorus (TP) and total nitrogen (TN) transported by 21 Finnish rivers to the northern Baltic Sea and analysed the flow-adjusted trends in the loads and concentrations from 1985 to 2006. We also related the loads to spatial and temporal patterns in catchment and agricultural characteristics. Agricultural load of TN increased, especially in the rivers discharging into the Bothnian Bay, while the load of TP decreased in most of the rivers, except those discharging into the Archipelago Sea. The trends may partly be related to a decrease in grassed area (TP, TN) and increased mineralisation (TN), but the available data on catchment and agricultural characteristics did not fully explain the observed pattern. Our study showed that data arising from relatively infrequent monitoring may prove useful for analysing long-term trend. The mutual correlation among the explaining variables hampered the analysis of the load generating factors.

Statistical Dimensioning of Nutrient Loading Reduction: LLR Assessment Tool for Lake Managers

Abstract Implementation of the EU Water Framework Directive (WFD) has set a great challenge on river basin management planning. Assessing the water quality of lakes and coastal waters as well as setting the accepted nutrient loading levels requires appropriate decision supporting tools and models. Uncertainty that is inevitably related to the assessment results and rises from several sources calls for more precise quantification and consideration. In this study, we present a modeling tool, called lake load response (LLR), which can be used for statistical dimensioning of the nutrient loading reduction. LLR calculates the reduction that is needed to achieve good ecological status in a lake in terms of total nutrients and chlorophyll a (chl-a) concentration. We show that by combining an empirical nutrient retention model with a hierarchical chl-a model, the national lake monitoring data can be used more efficiently for predictions to a single lake. To estimate the uncertainties, we separate the residual variability and the parameter uncertainty of the modeling results with the probabilistic Bayesian modeling framework. LLR has been developed to answer the urgent need for fast and simple assessment methods, especially when implementing WFD at such an extensive scale as in Finland. With a case study for an eutrophic Finnish lake, we demonstrate how the model can be utilized to set the target loadings and to see how the uncertainties are quantified and how they are accumulating within the modeling chain.

Statistical analysis of the effects on overland flow of spatial variability in soil hydraulic conductivity / Analyse statistique des effets de la variabilité spatiale de la conductivité hydraulique du sol sur l'écoulement de surface

Abstract The effects of spatial variation of the saturated hydraulic conductivity (K s ) of the soil on the variation of overland flow were tested by analysing 2000 synthetic rainfall—runoff events, all generated from real, observed rainfall events but with runoff modelled by a two-dimensional distributed model using different spatially variable K s fields in a small (12 ha) agricultural catchment. The purpose is to determine the influence of spatial variation in K s on runoff generation. The statistical measures used to describe the variation in the generated K s were its coefficient of variation and correlation length. Both of these had two levels of typical values obtained from field measurements in other studies. The storms were analysed at a general event level, first using simple graphical and statistical methods and then using analysis of variance (ANOVA). The observed scale of the spatial variation of K s does cause statistically significant variation in overland flow. The graphical analysis showed that the first flow peak in a multi-event storm had the largest variation and that differences were greater in the rising part of the hydrograph than in its recession. The greatest variation in overland flow was produced by the combination of the greater coefficient of variation and the longer correlation lengths. The smallest variation in overland flow was produced by the combination of the smaller coefficient of variation and the shorter correlation lengths. ANOVA showed that the coefficient of variation and correlation length alone did not explain all the variation of the total flow. ANOVA was not very useful due to the many restrictive assumptions that were not satisfied by the nature of the data and therefore analysis methods with less restrictive assumptions need to be tested.

Participatory operations model for cost-efficient monitoring and modeling of river basins — A systematic approach

The worldwide economic downturn and the climate change in the beginning of 21st century have stressed the need for cost efficient and systematic operations model for the monitoring and management of surface waters. However, these processes are still all too fragmented and incapable to respond these challenges. For example in Finland, the estimation of the costs and benefits of planned management measures is insufficient. On this account, we present a new operations model to streamline these processes and to ensure the lucid decision making and the coherent implementation which facilitate the participation of public and all the involved stakeholders. The model was demonstrated in the real world management of a lake. The benefits, pitfalls and development needs were identified. After the demonstration, the operations model was put into operation and has been actively used in several other management projects throughout Finland.

Assimilation of satellite data to 3D hydrodynamic model of Lake Säkylän Pyhäjärvi

To analyze the applicability of direct insertion of total suspended matter (TSM) concentration field based on turbidity derived from satellite data to numerical simulation, dispersion studies of suspended matter in Lake Säkylän Pyhäjärvi (lake area 154 km²; mean depth 5.4 m) were conducted using the 3D COHERENS simulation model. To evaluate the practicality of direct insertion, five cases with different initialization frequencies were conducted: (1) every time, when satellite data were available; (2) every 10 days; (3) 20 days; (4) 30 days; and (5) control run without repeated initialization. To determine the effectiveness of initialization frequency, three methods of comparison were used: simple spatial differences of TSM concentration without biomass in the lake surface layer; averaged spatial differences between initialization data and the forecasts; and time series of TSM concentration and observation data at 1 m depth at the deepest point of the lake. Results showed that direct insertion improves the forecast significantly, even if it is applied less often.

Probabilistic Evaluation of Ecological and Economic Objectives of River Basin Management Reveals a Potential Flaw in the Goal Setting of the EU Water Framework Directive

The biological status of European lakes has not improved as expected despite up-to-date legislation and ecological standards. As a result, the realism of objectives and the attainment of related ecological standards are under doubt. This paper gets to the bottom of a river basin management plan of a eutrophic lake in Finland and presents the ecological and economic impacts of environmental and societal drivers and planned management measures. For these purposes, we performed a Monte Carlo simulation of a diffuse nutrient load, lake water quality and cost-benefit models. Simulations were integrated into a Bayesian influence diagram that revealed the basic uncertainties. It turned out that the attainment of good ecological status as qualified in the Water Framework Directive of the European Union is unlikely within given socio–economic constraints. Therefore, management objectives and ecological and economic standards need to be reassessed and reset to provide a realistic goal setting for management. More effort should be put into the evaluation of the total monetary benefits and on the monitoring of lake phosphorus balances to reduce the uncertainties, and the resulting margin of safety and costs and risks of planned management measures.