Modelling of hydrologic processes and potential response to climate change through the use of a multisite SWAT

Hydrologic models that use components for integrated modelling of surface water and groundwater systems help conveniently simulate the dynamically linked hydrologic and hydraulic processes that govern flow conditions in watersheds. The Soil and Water Assessment Tool (SWAT) is one such model that allows continuous simulations over long time periods in the land phase of the hydrologic cycle by incorporating surface water and groundwater interactions. This study provides a verified structure for the SWAT to evaluate existing flow regimes in a small-sized catchment in Denmark and examines a simple simulation to help quantify the effects of climate change on regional water quantities. SWAT can be regarded among the alternative hydrologic simulation tools applicable for catchments with similar characteristics and of similar sizes in Denmark. However, the modellers would be required to determine a proper set of effective model parameters and agree on a proper balancing among different calibration sites during all parameter optimization trials.     

Landscape planning to reduce coastal eutrophication: agricultural practices and constructed wetlands

Southern Sweden suffers from coastal eutrophication and one reason is the high nitrogen load through rivers. The major part of this load originates from diffuse land-based sources, e.g. arable soil leaching. Effective reduction of load from such sources demand careful landscape analysis, combined with changed behaviour of the stakeholders. This study describes a chain of methods to achieve trustworthy management plans that are based on numerical modelling and stakeholders participation and acceptance. The effect of some measures was unexpected when modelling their impact on the catchment scale.Management scenarios to reduce riverine nitrogen load were constructed in an actor game (i.e. role-play) for the Genevadsån catchment in southern Sweden. The game included stakeholders for implementation of a loading standard for maximum nitrogen transport at the river mouth. Scenarios were defined after negotiation among involved actors and included changes in agricultural practices, improved wastewater treatment, and establishment of wetlands. Numerical models were used to calculate the nitrogen reduction for different measures in each scenario. An index model (STANK) calculated the root zone leaching of nitrogen from crops at four type farms. This generated input to a catchment scale model (HBV-N) and farm economics. The economic impact of different sets of remedial measures was evaluated for each type farm and then extrapolated to the catchment.The results from scenario modelling show that possible changes in agricultural practices (such as tuning, timing of fertilisation and ploughing, changed crop cultivation) could reduce the nitrogen load to the sea by some 30%, while wetland construction only reduced the original load by some 5%. In the most cost-effective scenario agricultural practices could reduce the riverine load by 86 t per year at a cost of 1.0 million SEK, while constructed wetlands only reduced the load by 14 t per year at a cost of 1.7 million SEK. Thus, changed agricultural practices can be the most effective and less expensive way to reduce nitrogen transport from land to the sea, while constructed wetlands with realistic allocations and sizes may only have small impact on riverine nitrogen transport from land to sea. The overall experience is that actor games and numerical modelling are useful tools in landscape planning for analysing stakeholders’ behaviour and the impact of measures to reduce coastal eutrophication.     

Impacts of climate change on phosphorus loading from a grassland catchment: Implications for future management

Dynamic modelling was used to quantify the impact of projected climate change, and potential changes in population and land use, on phosphorus (P) export from a sub-catchment in SW Ireland using the Generalised Watershed Loading Functions (GWLF) model. Overall the results indicated that the increase in annual total phosphorus loads attributable to climate change was greater than that from either population or land use change, and therefore that future climate variability will pose an increasingly significant threat to the successful long-term implementation of catchment management initiatives. The seasonal pattern in projected P export mirrored changes in streamflow, with higher rates between January and April and lower rates in summer. The potential reduction in export in summer was, however, negated when increases in population were included in simulations. A change in the slurry spreading period from that stipulated in national regulations to the months between April and September could potentially mitigate against future increases in dissolved P export in spring. The results indicate that projected changes in climate should be included when undertaking modelling exercises in support of decision making for catchment management plans.     

Towards quantification of uncertainty in predicting water quality failures in integrated catchment model studies

This paper describes the development and application of a method for estimating uncertainty in the prediction of sewer flow quantity and quality and how this may impact on the prediction of water quality failures in integrated catchment modelling (ICM) studies. The method is generic and readily adaptable for use with different flow quality prediction models that are used in ICM studies. Use is made of the elicitation concept, whereby expert knowledge combined with a limited amount of data are translated into probability distributions describing the level of uncertainty of various input and model variables. This type of approach can be used even if little or no site specific data is available. Integrated catchment modelling studies often use complex deterministic models. To apply the results of elicitation in a case study, a computational reduction method has been developed in order to determine levels of uncertainty in model outputs with a reasonably practical level of computational effort. This approach was applied to determine the level of uncertainty in the number of water quality failures predicted by an ICM study, due to uncertainty associated with input and model parameters of the urban drainage model component of the ICM. For a small case study catchment in the UK, it was shown that the predicted number of water quality failures in the receiving water could vary by around 45% of the number predicted without consideration of model uncertainty for dissolved oxygen and around 32% for unionised ammonia. It was concluded that the potential overall levels of uncertainty in the ICM outputs could be significant. Any solutions designed using modelling approaches that do not consider uncertainty associated with model input and model parameters may be significantly over-dimensioned or under-dimensioned. With changing external inputs, such as rainfall and river flows due to climate change, better accounting for uncertainty is required.     

A comparison of SWAT, HSPF and SHETRAN/GOPC for modelling phosphorus export from three catchments in Ireland

Recent extensive water quality surveys in Ireland revealed that diffuse phosphorus (P) pollution originating from agricultural land and transported by runoff and subsurface flows is the primary cause of the deterioration of surface water quality. P transport from land to water can be described by mathematical models that vary in modelling approach, complexity and scale (plot, field and catchment). Here, three mathematical models (soil water and analysis tools (SWAT), hydrological simulation program-FORTRAN (HSPF) and système hydrologique Européen TRANsport (SHETRAN)/grid oriented phosphorus component (GOPC)) of diffuse P pollution have been tested in three Irish catchments to explore their suitability in Irish conditions for future use in implementing the European Water Framework Directive. After calibrating the models, their daily flows and total phosphorus (TP) exports are compared and assessed. The HSPF model was the best at simulating the mean daily discharge while SWAT gave the best calibration results for daily TP loads. Annual TP exports for the three models and for two empirical models were compared with measured data. No single model is consistently better in estimating the annual TP export for all three catchments.     

Photogrammetric 3D modelling and mechanical analysis of masonry arches: An approach based on a discontinuous model of voussoirs

This article shows the application of close range photogrammetry to the generation of accurate 3D geometric models for the subsequent evaluation of the condition state of historical masonry bridge arches by means of numerical analysis. The arch geometry in the model was obtained from each individual voussoir or ashlar with its own contour geometry, which was obtained by close range photogrammetry. From this precise geometrical model, mechanical modelling tools and finite elements analysis were applied to accomplish two main goals: to estimate the failure load considering the arch stability using a discontinuous model of voussoirs assembled without tension at the interfaces, and to obtain the distribution of stresses into each voussoir. The obtained results by means of this procedure are compared with those obtained by rigid blocks limit analysis with regular geometry.     

Quantifying costs and lengths of urban drainage systems with a simple static sewer infrastructure model

A generic model is introduced that is capable of quantitatively representing the combined sewer infrastructure of a settlement. It consists of a catchment area module, which calculates the length and size distribution of the needed sewer pipes on the basis of rain, housing densities and area size. These results are fed into the sewer construction costs module in order to estimate the combined sewer costs of the entire catchment area.

The model could be successfully fitted to existing Swiss sewer systems, indicating that it can emulate their principal characteristics. It could also identify fundamental differences in sewer designs in cities with historic roots. The results confirm that there are economies of scale for combined sewer systems in Switzerland. The modelling approach proved to be an effective tool for understanding the factors underlying the cost structure for water network infrastructures.     

A cross analysis of existing methods for modelling household appliance use

This paper presents a cross-analysis of the existing methods for modelling the use of household appliances and aims to provide insights into modelling approaches for researchers and designers. Five factors regarding appliance use modelling that have a significant impact on the modelling performance are defined: consideration of the intra/inter-household variation, consideration of the influence of socio-demographic conditions, time resolution of the data, quantification of model calibration parameters and applicability to a variety of modelling contexts. Four existing modelling methods commonly used in literature for modelling appliance use are studied to address these factors. Monitored data of 333 multi-family buildings in Japan and a Japanese time use survey are used in the cross-analysis to simulate the switch-on time profiles for the case of washing machines. The design of future research studies (including monitoring strategies, modelling and sample sizes) are discussed to further improve the ability to model home appliance use.     

Flood Generation Modelling

This paper summarizes recent research and development of a particular process-based runoff generation model, the Institute of Hydrology Distributed Model. Surface and subsurface flow equations are linked in a hydrologically appropriate system to allow simulation of catchment runoff processes. Predictions can be made of channel flow, surface runoff and subsurface flow, pressure potentials and water contents. The structure and methods of the model are described and its data and computing requirements are outlined. Field and systematic applications are discussed, together with the work carried out on providing guidelines for use for the wider hydrological community.     

Modelling long-term stream acidification in the chemically heterogeneous Upper Severn catchment, Mid-Wales

A two-box version of the long-term acidification model MAGIC is applied to the Upper Severn catchment, Mid-Wales. Comparison between modelled output and the observed stream- and groundwater chemistry points to the limitations of modelling, due to the inherent complexity and variability in the catchment hydrology, soils, geology and chemistry. The MAGIC model is used to produce long-term hind- and forecast predictions of average stream-, soil- and groundwater chemistry, and to simulate long-term changes in sulfate and nitrate deposition, in line with current proposals of reduction. Changes in flow-routing pathways between soil- and groundwater are simulated and the long-term effects on streamwater quality noted. The use of a long-term acidification model enabled the simulation of streamwater quality under these different case scenarios. However, the modelled output is insensitive to depositional and flow routing changes, indicating that catchment processes are not being represented to a sufficient degree. Changes in simulated output as a result of increased acidic deposition are not statistically significant, lying within the variance of long-term observed data. Simulated changes in flow routing suggest a lack of model sensitivity, in terms of the effect on stream chemistry. The need for large amounts of measured data to ensure correct model representation of the hydrology, chemistry and the heterogeneous/variable nature of upland catchments is outlined. It is vital that these long-term data are available to ensure that problems do not arise due to over-reliance by catchment managers on potentially unreliable modelled output.     

Modelling on-site detention on a catchment-wide basis

Many countries are either currently using or considering the use of on-site detention (OSD) as a structural flood mitigation method. On-site detention is a structural element of a property drainage system that limits the site discharge of stormwater using outlet restriction devices. The excess stormwater runoff is temporarily stored on site in underground tanks or above-ground storage areas until the storm event recedes.

Sydney, Australia, has a stormwater system that is completely separate from the sewerage system. The stormwater systems are mainly managed by the 43 local councils and most of these use OSD as a means of reducing site discharge of stormwater, thereby relieving catchment flooding. Sheas Creek is an urbanized catchment that lies within the South Sydney City Council Local Government Area. Since 1984 an OSD policy has been implemented in the Sheas Creek catchment. The associated design code, like most others in Sydney, is based on discharge from individual properties without consideration of runoff from other parts of the catchment. This design code is therefore not based on a total catchment approach.

The objective of this study is to assess the effectiveness of OSD in a catchment-wide manner. More specifically, to see how existing and planned OSD affects flooding in the Sheas Creek catchment, and to test the effectiveness of the current rate of permissible site discharge (PSD). The study also looks at the effectiveness of OSD when different spatial distributions are used across a catchment. The methodology involved using a computer rainfall–runoff model, OSDSAX, which is based on the ILLUDAS model. This was configured for the Sheas Creek catchment and was calibrated to match flood level data recorded during four large storm events. The model was then adopted to investigate the impact of OSD. Various scenarios were tested to satisfy the objectives of the study. Some of the results challenge conventional wisdom and these arise from catchment-specific characteristics. The analysis shows that the perceived beneficial effects of OSD are in some cases unrealistic and that catchment modelling is required to test and quantify the actual impacts for specific catchments.     

GIS-MODFLOW: Ein kleines OpenSource-Werkzeug zur Anbindung von GIS-Daten an MODFLOW

The numerical model MODFLOW (Harbaugh 2005) is an efficient and up-to-date tool for groundwater flow modelling. On the other hand, Geo-Information-Systems (GIS) provide useful tools for data preparation and visualization that can also be incorporated in numerical groundwater modelling. An interface between both would therefore be useful for many hydrogeological investigations. To date, several integrated stand-alone tools have been developed that rely on MODFLOW, MODPATH and transport modelling tools. Simultaneously, several open source-GIS codes were developed to improve functionality and ease of use. These GIS tools can be used as pre- and post-processors of the numerical model MODFLOW via a suitable interface. Here we present GIS-MODFLOW as an open-source tool that provides a new universal interface by using the ESRI ASCII GRID data format that can be converted into MODFLOW input data. This tool can also treat MODFLOW results. Such a combination of MODFLOW and open-source GIS opens new possibilities to render groundwater flow modelling, and simulation results, available to larger circles of hydrogeologists.     

Integrated river flow modelling: A case study

The paper presents a holistic approach to river flow modelling in which catchment rainfall-runoff, sewer hydrodynamic and river hydrodynamic models are linked together and applied to the Bradford catchment (UK). The catchment features steep gradients, flashy supercritical flow in combination with dry bed condition and is highly urbanised. Given this complexity and the paucity of data, a holistic approach was found essential, although its application proved challenging.

Most important uncertainties inherent in each sub-model were assessed individually as well as propagation effects through the integrated model. The relative contribution of uncertainty sources to the total uncertainty in river flow predictions was quantified using the concept of variance decomposition. The results show that uncertainties in model structure and rainfall input in the rainfall-runoff model were significant. However, within the river hydrodynamic model, uncertainties propagated from the rainfall-runoff model were less apparent due to additional uncertainty arising from the urban drainage system.     

Linking catchment characteristics and water chemistry with the ecological status of Irish rivers

Requirements of the EU Water Framework Directive for the introduction of ecological quality objectives for surface waters and the stipulation that all surface waters in the EU must be of 'good' ecological status by 2015 necessitate a quantitative understanding of the linkages among catchment attributes, water chemistry and the ecological status of aquatic ecosystems. Analysis of lotic ecological status, as indicated by an established biotic index based primarily on benthic macroinvertebrate community structure, of 797 hydrologically independent river sites located throughout Ireland showed highly significant inverse associations between the ecological status of rivers and measures of catchment urbanisation and agricultural intensity, densities of humans and cattle and chemical indicators of water quality. Stepwise logistic regression suggested that urbanisation, arable farming and extent of pasturelands are the principal factors impacting on the ecological status of streams and rivers in Ireland and that the likelihood of a river site complying with the demands of the EU Water Framework Directive, and be of 'good' ecological status, can be predicted with reasonable accuracy using simple models that utilise either widely available landcover data or chemical monitoring data. Non-linear landcover and chemical 'thresholds' derived from these models provide a useful tool in the management of risk in catchments, and suggest strongly that more careful planning of land use in Ireland is essential in order to restore and maintain water quality as required by the Directive.     

Peak Demands from Spray Irrigation

Although irrigation accounts for less than 2% of water use in the UK, direct abstraction for spray irrigation can be a significant user in certain catchments in dry summers. Peak demand is expected to grow nationally by 1–2% per annum on average, but this growth varies locally. Water resource planners need to know the peak demands and how they are likely to grow within each catchment or aquifer, and the likely local annual variation and timing of demand. This paper discusses how recent developments in irrigation modelling combined with the application of a 'geographic information system'can produce such forecasts, taking into account spatial variation in soils, climate, cropping and irrigation practice.     

Modelling Cryptosporidium oocysts transport in small ungauged agricultural catchments

Cryptosporidium is an environmentally robust pathogen that has caused severe waterborne disease outbreaks worldwide. The main source of zoonotic Cryptosporidium parvum oocysts in human drinking water is likely to be from farm animals via catchment pathways with water as the main transport vector. The vast majority of small agricultural catchments are ungauged therefore it is difficult to use a process model to predict and understand the mechanisms and activities that regulate the risk of surface water contamination from agricultural areas. For this study, two ungauged agricultural catchments in Ireland were used to model Cryptosporidium oocyst transport using SWAT2005 on a daily basis with reference data from adjacent catchment gauging stations. The results indicated that SWAT2005 could simulate stream flow with good agreement between prediction and observation on a monthly basis (R² from 0.94 to 0.83 and E (efficiency) from 0.92 to 0.66), but Cryptosporidium oocyst concentration results were less reliable (R² from 0.20 to 0.37, P < 0.05; with poor E −0.37 to −2.57). A sensitivity analysis using independent parameter perturbation indicated that temperature was the most important parameter regulating oocyst transport in the study catchments and that the timing of manure application relative to the occurrence of water runoff event was critical. The results also showed that grazing management had little influence on predicted oocyst transport while fields fertilized with manure were the key critical source areas for microbial contaminations in the study catchments. It was concluded that the approach presented could be used to assist with understanding the epidemiology of waterborne cryptosporidiosis outbreaks and to improve catchment management for the safety of the general public health.     

Building response to tunnelling

Understanding how buildings respond to tunnelling-induced ground movements is an area of great importance for urban tunnelling projects, particularly for risk management. In this paper, observations of building response to tunnelling, from both centrifuge modelling and a field study in Bologna, are used to identify mechanisms governing the soil–structure interaction. Centrifuge modelling was carried out on an 8-m-diameter beam centrifuge at Cambridge University, with buildings being modelled as highly simplified elastic and inelastic beams of varying stiffness and geometry. The Bologna case study presents the response of two different buildings to the construction of a sprayed concrete lining (SCL) tunnel, 12 m in diameter, with jet grouting and face reinforcement.In both studies, a comparison of the building settlement and horizontal displacement profiles, with the greenfield ground movements, enables the soil structure interaction to be quantified. Encouraging agreement between the modification to the greenfield settlement profile, displayed by the buildings, and estimates made from existing predictive tools is observed. Similarly, both studies indicate that the horizontal strains, induced in the buildings, are typically at least an order of magnitude smaller than the greenfield values. This is consistent with observations in the literature. The potential modification to the settlement distortions is shown to have significant implications on the estimated level of damage. Potential issues for infrastructures connected to buildings, arising from the embedment of rigid buildings into the soil, are also highlighted.     

空间索杆式展开结构的动力学研究与分析

本文针对空间索杆式展开结构的特点,利用多刚体动力学的研究成果建立展开过程分析的动力学模型,分析了约束方程及其雅可比矩阵的形成,结合系统的约束方程来分析机构的运动状态,最后对系统的机构单元进行数值仿真计算,得到了对伸展臂的指标确定和设计有重要指导意义的数值分析结果.计算结果表明,文中结构模型的设计方案是可行的.     

Use of numerical models for determination of best sampling locations for monitoring of large lakes

The implementation of the European Union Water Framework Directive (WFD) that requires all surface waters to achieve at least good status by year 2015 presents a challenge to local authorities responsible for the monitoring programmes. Obtaining a single representative value for each water quality parameter may be extremely difficult to achieve in the case of large lakes, which may be characterised by significant spatial and temporal variation of water quality parameters. The aim of this paper is to present a methodology, which can support the decision making as to the best locations for water quality sampling when developing monitoring systems of large lakes. The methodology is based on three-dimensional hydrodynamic and a conservative tracer transport numerical modelling and utilises the concept of flushing and residence time. The 3D numerical model of Lough Corrib located in the west of Ireland was created and used to calculate its residence time and flushing pathways. Based on the results it was possible to identify the areas in the lake that are characterised by the local residence time values close to the lake's average as well as by the values significantly lower and higher. Three water classes have been introduced and the authors recommend that sampling takes place in all three classes at various frequencies. Spatial distribution of the flushing pathways allows identifying the areas in the lake that best represent the lake's average conditions both in the long term and seasonally, where monitoring can be carried out at the required frequency; worst affected areas can also be identified. The methodology can be used to improve robustness of the monitoring programme and may also contribute towards the reduction of both sampling and analytical costs, both at the design and operational stages.