Catchment modelling

The scientific initiative Prediction in Ungauged
Basins (PUB) (2003–2012 by the IAHS) put considerable effort
into improving the reliability of hydrological models to
predict flow response in ungauged rivers. PUB’s collective
experience advanced hydrologic science and defined guidelines
to make predictions in catchments without observed
runoff data. At present, there is a raised interest in applying
catchment models to large domains and large data samples
in a multi-basin manner, to explore emerging spatial patterns
or learn from comparative hydrology. However, such modelling
involves additional sources of uncertainties caused by
the inconsistency between input data sets, i.e. particularly
regional and global databases. This may lead to inaccurate
model parameterisation and erroneous process understanding.
In order to bridge the gap between the best practices
for flow predictions in single catchments and multi-basins
at the large scale, we present a further developed and slightly
modified version of the recommended best practices for PUB
by Takeuchi et al. (2013). By using examples from a recent
HYPE (Hydrological Predictions for the Environment) hydrological
model set-up across 6000 subbasins for the Indian
subcontinent, named India-HYPE v1.0, we explore the PUB
recommendations, identify challenges and recommend ways
to overcome them. We describe the work process related to
(a) errors and inconsistencies in global databases, unknown
human impacts, and poor data quality; (b) robust approaches
to identify model parameters using a stepwise calibration approach,
remote sensing data, expert knowledge, and catchment
similarities; and (c) evaluation based on flow signatures
and performance metrics, using both multiple criteria and
multiple variables, and independent gauges for “blind tests”.
The results show that despite the strong physiographical gradient
over the subcontinent, a single model can describe the
spatial variability in dominant hydrological processes at the
catchment scale. In addition, spatial model deficiencies are
used to identify potential improvements of the model concept.
Eventually, through simultaneous calibration using numerous
gauges, the median Kling–Gupta efficiency for river
flow increased from 0.14 to 0.64. We finally demonstrate the
potential of multi-basin modelling for comparative hydrology
using PUB, by grouping the 6000 subbasins based on
similarities in flow signatures to gain insights into the spatial
patterns of flow generating processes at the large scale.

Computer models, especially conceptual models,
are frequently used for catchment hydrology studies. Teaching
hydrological modeling, however, is challenging, since
students have to both understand general model concepts and
be able to use particular computer programs when learning
to apply computer models. Here we present a new version
of the HBV (Hydrologiska Byr°ans Vattenavdelning) model.
This software provides a user-friendly version that is especially
useful for education. Different functionalities, such as
an automatic calibration using a genetic algorithm or a Monte
Carlo approach, as well as the possibility to perform batch
runs with predefined model parameters make the software
interesting especially for teaching in more advanced classes
and research projects. Different teaching goals related to hydrological
modeling are discussed and a series of exercises is
suggested to reach these goals.

The allocation of groundwater resources has been a challenge for many years due to its unforeseen side effect and lag time issues, which are often overlooked. The full impact of groundwater utilization/abstraction takes time to realize its effect at its full. In this paper, long‐term effects and groundwater dynamics were assessed using a water balance model and a time series analysis, respectively. Undeveloped groundwater systems are commonly found in a state of equilibrium, where, on average, equal amounts of water are recharged and discharged. A water budget is a static accounting of the state of the system at a given time, often before the system is developed. Water balance analysis was carried out together with the groundwater through flow, hydrograph, and surface‐groundwater interaction analysis (base flow index) to develop a conceptual water balance model, which is a very basic representation of a complex natural aquifer system and is instrumental to constrain and build a robust numerical model that can be readily justified and updated. A noble approach was employed to assess and constrain the discharge coming out of the model area to sustain the lake level, located to the north of the study area, using the whole lake catchment and lake water balance analysis. Based on the lake water balance, there is a deficit between input and output computation, and hence there should be a groundwater input to sustain the historical lake area. The analysis showed that the model area contributes 40% of the lake catchment, and hence the portion of the groundwater inflow feeding the lake was computed. This is one of the means to constrain the discharge, which adds more confidence to the recharge estimation. This is very important because the size of a sustainable groundwater development usually depends on how much of the discharge from the system can be captured by the development. Capture is independent of the recharge. Instead, it depends on the dynamic response of the aquifer system to the development. The idea that knowing the recharge is important in determining the size of a sustainable groundwater development is a myth and has no basis. The important entity in determining how a groundwater system reaches a new equilibrium is capture. How capture occurs in an aquifer system is a dynamic process. Following this study, lake water balance assessment was indirectly considered as prior information for the numerical model calibration of the discharge from the model area using a conductance parameter. Conductance is a key parameter to estimate the discharge volume together with the change in the simulated hydraulic head between time steps. The water balance error highlights which one is more sensitive, and this could help to assist in planning for future data collection/field work and where to invest the money. The water balance computation helps to figure out the degree of surface‐groundwater interaction, uncertainty, sensitive parameter, helps in the decision to invest time and money, and operates as a cross check with other analytical or numerical modelling.

La microcuenca de drenaje de la quebrada Curucutí se ubica en la vertiente norte del Macizo del Ávila (10º33’08"-10º36’23" LN y 66º57’38"-66º59’14" LO), en el sector centro occidental del estado Vargas (Venezuela). Este sistema fue una de las más de veinte cuencas que se activaron hidromorfodinámicamente, como respuesta a las excepcionales precipitaciones ocurridas en Diciembre de 1999, en el Litoral Central de Venezuela. Es por ello que el propósito de este trabajo es, analizar e interpretar la dinámica hidrogeomorfológica de la microcuenca de drenaje de la quebrada Curucutí, en términos del control que ejercen sus parámetros morfométricos en las características de la respuesta hidrológica. La metodología comprendió: (a) cálculos y mediciones de parámetros morfométricos; (b) cálculo del tiempo de concentración; y (c) estimación de los hidrogramas unitarios y caudales pico de crecientes. La microcuenca de drenaje de la quebrada Curucutí, es un sistema hidrogeomorfológico cuya respuesta hidrológica está determinada por la pequeña área del mismo, fuertes pendientes en las vertientes y cauces del sector montañoso, la densidad de drenaje media, el orden 5 de la microcuenca, una relación de bifurcación media de 3,73, alta torrencialidad, las dimensiones de las tormentas y la intensidad y duración de las lluvias. Los cortos tiempos de concentración, así como las magnitudes estimadas de los caudales pico de crecientes y los picos y tiempos al pico de los hidrogramas unitarios obtenidos, corroboran la influencia que ejercen las características fisiográficas de la microcuenca y la estructura de la red de drenaje, en las respuestas rápidas y violentas del sistema. Ello define escenarios críticos de inundaciones, para eventos de períodos de retorno de 50, 100 y 500 años principalmente, y en el peor de los casos de 1000 años, para lluvias de 1 hora de duración.

A method is presented to analyze the interaction between groundwater and Lake Linlithgow (Australia) as a case study. A simplistic approach based on a " node " representing the groundwater component is employed in a spreadsheet of water balance modeling to analyze and highlight the effect of groundwater on the lake level over time. A comparison is made between the simulated and observed lake levels over a period of time by switching the groundwater " node " on and off. A bucket model is assumed to represent the lake behavior. Although this study demonstrates the understanding of Lake Linlithgow's groundwater system, the current model reflects the contemporary understanding of the local groundwater system, illustrates how to go about modeling in data‐scarce environments, and provides a means to assess focal areas for future data collection and model improvements. Results show that this approach is convenient for getting first‐hand information on the effect of groundwater on wetland or lake levels through lake water budget computation via a node representing the groundwater component. The method can be used anywhere and the applicability of such a method is useful to put in place relevant adaptation mechanisms for future water resources management, reducing vulnerability and enhancing resilience to climate change within the lake basin.

Increasing pressures on water quality due to intensification of agriculture have increased the need for environmental modelling to accurately simulate the movement of diffuse (nonpoint) nutrients in catchments. As hydrological flows drive the movement and attenuation of nutrients, individual hydrological processes in models should be adequately represented for water quality simulations to be meaningful. In particular, the relative contribution of groundwater and surface runoff to rivers is of interest, as, for example, higher nitrate concentrations in surface waters are strongly linked to catchments with proportionately larger groundwater contributions to the river. In this study, uncertainty analysis was used to investigate parameter sensitivities and flow partitioning of three conceptual hydrological models simulating 31 Irish catchments. We compared two established conceptual hydrological models (NAM and SMARG) and a new model (SMART), produced especially for water quality modelling. In addition to the criteria that assess streamflow simulations, a ratio of average groundwater contribution to total streamflow was calculated for all simulations over the 16 year study period. As measured time-series of groundwater contributions to streamflow are not available at catchment scale, the groundwater ratios were evaluated against average annual indices of base flow (from the OPW) and estimates of deep groundwater flow (from the Geological Survey of Ireland) for each catchment. The exploration of sensitivities of internal flow path partitioning was a specific focus to assist in evaluating model performances. Results highlight that model structure has a strong impact on simulated groundwater flow path contributions. Sensitivities to the internal pathways in the models are not reflected in the usual (flood forecasting) performance criteria results. This demonstrates that simulated groundwater contribution should be constrained by independent data to ensure results within realistic bounds if such models are to be used in the broader environmental sustainability decision making context.

In western Victoria, south east Australia, the land clearing during European settlement has had significant impacts on the water table to rise. On the other hand, water table have been declining for at least the last 10-15 years, and this is attributed to the consistently low rainfall for these years, but over the same period of time there has been substantial change in land use, with grazing land replaced by cropping and tree plantations appearing in some areas resulting to decline the water table. The aim of the present study is to model groundwater level fluctuations, relating groundwater levels to precipitation excess, and the impact of landuse change could be assessed. To this purpose, a specific type of transfer function-noise model, the Predefined Impulse Response Function In Continuous Time (PIRFICT) model and an auto-regressive model, Hydrograph Analysis: Rainfall and Time Trends (HARTT) are applied to quantify the relative influence of climatic variable and land use change on the course of groundwater level and to characterize the groundwater system. In PIRFICT modelling, the spatial differences in the groundwater system are determined by the system properties, while temporal variation is driven by the dynamics of the input into the system. It became evident that the no evapotranspiration effect assumption of the HARTT becomes a serious drawback in areas with shallow groundwater levels, because of significant seasonal evaporation component as identified in PIRFICT modelling. However the average results of estimated trend using PIRFICT models and the HARTT models differ only slightly, despite having clear different theoretical stating point. A PIRFICT model was found a better way of estimating the non-climate trend because the climatic variables (rainfall and evapotranspiration) are accounted for. Most of the groundwater level fluctuations are explained by climatic variables and non-climatic trend (90%). The average trend is -0.029 m/yr which is insignificant. Though, the trend estimate from bores screened in Port Campbell Limestone is relatively significant (-0.3 m/yr), it was mainly due to groundwater pumping from the nearby production bores for irrigation purpose. The results are validated and cross checked using estimated parameters with the physical knowledge of the area. From this study there is no indication that the groundwater table was rising/falling due to changes in landuse, at least not during the observation period. From HARTT analysis, the impact of recharge was felt with no delay period (less than a month lag time) on the course of groundwater level. In continuity with this, PIRFICT modeling further identified how long the impact already felt stays in the system (estimated 5.7 years on average). Therefore, an explicit effect of massive clearing on the water table could not be detected across the study area, owing to the short groundwater response times and the completion of most clearing long time ago. This will have an implication for mitigation of dry land salinity in particular and water resources management in general. However, such short response times disagree with the currently assumed slow-reacting groundwater flow system concepts. The lag times and processes identified in this study are related to time needed for the groundwater storage to move to a new state of hydrologic (physical, pressure-related) equilibrium. This will improve our knowledge of the hydrogeology and thus groundwater flow systems across the Victorian Volcanic plain.

Human-induced changes to river loads of nutrients and sediments pose a significant threat to marine ecosystems. Ongoing land-use change can further increase these loads, and amplify the impacts of land-based threats on vulnerable marine ecosystems. Consequently, there is a need to assess these threats and prioritise actions to mitigate their impacts. A key question regarding prioritisation is whether actions in catchments to maintain coastal-marine water quality can be spatially congruent with actions for other management objectives, such as conserving terrestrial biodiversity. In selected catchments draining into the Gulf of California, Mexico, we employed Land Change Modeller to assess the vulnerability of areas with native vegetation to conversion into crops, pasture, and urban areas. We then used SedNet, a catchment modelling tool, to map the sources and estimate pollutant loads delivered to the Gulf by these catchments. Following these analyses, we used modelled river plumes to identify marine areas likely influenced by land-based pollutants. Finally, we prioritised areas for catchment management based on objectives for conservation of terrestrial biodiversity and objectives for water quality that recognised links between pollutant sources and affected marine areas. Our objectives for coastal-marine water quality were to reduce sediment and nutrient discharges from anthropic areas, and minimise future increases in coastal sedimentation and eutrophication. Our objectives for protection of terrestrial biodiversity covered species of vertebrates. We used Marxan, a conservation planning tool, to prioritise interventions and explore spatial differences in priorities for both objectives. Notable differences in the distributions of land values for terrestrial biodiversity and coastal-marine water quality indicated the likely need for trade-offs between catchment management objectives. However, there were priority areas that contributed to both sets of objectives. Our study demonstrates a practical approach to integrating models of catchments, land-use change, and river plumes with conservation planning software to inform prioritisation of catchment management.

The objective of this study is to construct a balanced chlorine budget for a small forested catchment, focusing on the interaction between chloride (Clinorg) and organic-matter-bound chlorine (Clorg). Data from the actual catchment are combined with secondary data from other sites to elucidate more clearly which parts of the cycle are fairly well known and which are more or less unknown. The budget calculations show that the principal input and output fluxes of Cl in the catchment are inorganic but that the main pool is Clorg in the soil. In addition, the budget calculations suggest that a considerable portion of Clinorg in soil is transformed to Clorg and subsequently leached to deeper soil layers, that net mineralization of Clorg takes place in soil, preferably in deeper soil layers, and that degrading organic matter is a major source of Clinorg in runoff. The loss of Clorg through runoff is small to negligible in relation to other fluxes. It appears as if dry deposition of Clinorg is at risk of being underestimated if Clinorg is assumed to be conservative in soil. The pool of organic-matter-bound chlorine in soil is considerably larger than the annual flux of chloride through the system. The estimates suggest that the amount of Clorg in the upper 40 cm of the soil at the investigated site is approximately twice as large as the Clinorg. Furthermore, the amount of Clorg biomass is small in relation to the occurrence of Clorg in soil. Finally, the estimates indicate that the transport of volatile Clorg from the soil to the atmosphere may influence the chlorine cycle.

Degradation of coastal ecosystems in the Great Barrier Reef (GBR) lagoon, Australia, has been linked with increased land-based runoff of suspended solids, nutrients and pesticides since European settlement. This study estimated the increase in river loads for all 35 GBR basins, using the best available estimates of pre-European and current loads derived from catchment modelling and monitoring. The mean annual

Quantification of streamflow characteristics in ungauged catchments remains
a challenge. Hydrological modeling is often used to derive flow time series and to calculate
streamflow characteristics for subsequent applications that may differ from those envisioned
by the modelers. While the estimation of model parameters for ungauged catchments is
a challenging research task in itself, it is important to evaluate whether simulated time
series preserve critical aspects of the streamflow hydrograph. To address this question, seven
calibration objective functions were evaluated for their ability to preserve ecologically relevant
streamflow characteristics of the average annual hydrograph using a runoff model, HBV-light,
at 27 catchments in the southeastern United States. Calibration trials were repeated 100 times
to reduce parameter uncertainty effects on the results, and 12 ecological flow characteristics
were computed for comparison. Our results showed that the most suitable calibration strategy
varied according to streamflow characteristic. Combined objective functions generally gave
the best results, though a clear underprediction bias was observed. The occurrence of low
prediction errors for certain combinations of objective function and flow characteristic
suggests that (1) incorporating multiple ecological flow characteristics into a single objective function would increase model accuracy, potentially benefiting decision-making processes;
and (2) there may be a need to have different objective functions available to address specific
applications of the predicted time series.

Land use is a predominant threat to the ecological integrity of streams and rivers. Understanding land use-water quality interactions is essential for the development and prioritization of management strategies and, thus, the improvement of water quality. Weighting schemes for land use have recently been employed as methods to advance the predictive power of empirical models, however, their performance has seldom been explored for various water quality parameters. In this work, multiple landscape composition metrics were applied within headwater catchments of central europe to investigate how weighting land use with certain combinations of spatial and topographic variables, while implementing alternate distance measures and functions, can influence predictions of water quality. the predictive ability of metrics was evaluated for eleven water quality parameters using linear regression. Results indicate that stream proximity, measured with Euclidean distance, in combination with slope or log-transformed flow accumulation were dominant factors affecting the concentrations of pH, total phosphorus, nitrite and orthophosphate phosphorus, whereas the unweighted land use composition was the most effective predictor of calcium, electrical conductivity, nitrates and total suspended solids. Therefore, both metrics are recommended when examining land use-water quality relationships in small, submontane catchments and should be applied according to individual water quality parameter. It has been widely acknowledged that the ecological integrity of streams and rivers is intrinsically linked to the surrounding landscape 1-3. Riverine systems are amongst the most productive and biodiverse ecosystems 4 , yet extreme anthropogenic pressure has threatened the essential goods and services provided by tributaries 5. The protection of freshwater resources and ecosystems requires an understanding of the impacts from the encompassing landscape. Although land use-water quality interactions have been extensively researched, a comprehension of such relationships remains a complex endeavor. To discern the effects of land use on water quality, initial investigations frequently employed land use composition (i.e., the proportion of each land use category) as a predictor of stream condition (e.g. 6,7). While the composition of land use plays a crucial role on water quality, this rudimentary measure assumes that each proportion imposes an equal influence 8. Recently, the importance of spatial scale and topography has been corroborated in the contemporary understanding of land use-water quality interactions 8,9. Nevertheless, the intricate patterns and natural gradients of a terrestrial landscape, as well as scale-dependent mechanisms, make it difficult for empirical models to be assessed 2. The integration of spatially-explicit landscape features and processes with land use data is crucial for providing more accurate information on how land use can impact concentrations of water quality parameters (WQP). With the application of Geographic Information System (GIS) technologies, broadly-applicable weighting schemes have been established as methods to consider the spatial and topographic components of individual land use types on stream condition. Under the assumption that land located close to the stream generally has a larger influence on water quality than land located further away 8,10-14 , distance-weighted metrics have been implemented into studies to account for the spatial proximity of land use 10,11,15-18. In this method, a distance decay function is used, assigning weights to observations based on the hydrologic distance to the stream or sampling