Pub Date : 2023-08-29DOI: 10.5194/hess-27-3125-2023
Moreen Willaredt, T. Nehls, A. Peters
Abstract. Constructed Technosols are an important means of substituting natural soil material, such as peat and geogenic material, for use in urban green infrastructure. One characteristic of Technosols important to their role in urban green infrastructure, specifically with respect to urban water management, is their soil hydraulic properties (SHPs). The SHPs depend on the composition of the constructed Technosols (e.g. their components and their mixing ratio). The diversity of possible components and the infinite number of mixing ratios practically prohibit the experimental identification of the composition needed to achieve suitable soil hydrological functions. In this study, we propose a compositional model for predicting the water retention curves (WRCs) of any binary mixture based on the measured WRCs of its two pure components only (basic scheme) or with one additional mixture (extended scheme). The unsaturated hydraulic conductivity curves (HCCs) are predicted based on the modelled WRCs. The compositional model is developed from existing methods for estimating the porosity of binary mixtures. The model was tested on four data sets of measured WRCs of different binary mixtures. The distribution of water and air in 50 cm high soil columns filled with these mixtures was predicted under hydrostatic conditions in order to assess their suitability for typical urban applications. The difference between the maxima of the pore size distributions ΔPSDmax (m) of the components indicates the applicability of the compositional approach. For binary mixtures with small ΔPSDmax, the water content deviations between the predicted and the measured WRCs range from 0.004 to 0.039 cm3 cm−3. For mixtures with a large ΔPSDmax, the compositional model is not applicable. The prediction of the soil hydraulic properties of any mixing ratio facilitates the simulation of flow and transport processes in constructed Technosols before they are produced (e.g. for specific urban water management purposes).
{"title":"Predicting soil hydraulic properties for binary mixtures – concept and application for constructed Technosols","authors":"Moreen Willaredt, T. Nehls, A. Peters","doi":"10.5194/hess-27-3125-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3125-2023","url":null,"abstract":"Abstract. Constructed Technosols are an important means of substituting natural soil material, such as peat and geogenic material, for use in urban green infrastructure. One characteristic of Technosols important to their role in urban green infrastructure, specifically with respect to urban water management, is their soil hydraulic properties (SHPs). The SHPs depend on the composition of the constructed Technosols (e.g. their components and their mixing ratio). The diversity of possible components and the infinite number of mixing ratios practically prohibit the experimental identification of the composition needed to achieve suitable soil hydrological functions. In this study, we propose a compositional model for predicting the water retention curves (WRCs) of any binary mixture based on the measured WRCs of its two pure components only (basic scheme) or with one additional mixture (extended scheme). The unsaturated hydraulic conductivity curves (HCCs) are predicted based on the modelled WRCs.\u0000The compositional model is developed from existing methods for estimating the porosity of binary mixtures. The model was tested on four data sets of measured WRCs of different binary mixtures. The distribution of water and air in 50 cm high soil columns filled with these mixtures was predicted under hydrostatic conditions in order to assess their suitability for typical urban applications. The difference between the maxima of the pore size distributions ΔPSDmax (m) of the components indicates the applicability of the compositional approach. For binary mixtures with small ΔPSDmax, the water content deviations between the predicted and the measured WRCs range from 0.004 to 0.039 cm3 cm−3. For mixtures with a large ΔPSDmax, the compositional model is not applicable. The prediction of the soil hydraulic properties of any mixing ratio facilitates the simulation of flow and transport processes in constructed Technosols before they are produced (e.g. for specific urban water management purposes).\u0000","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46709478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-28DOI: 10.5194/hess-27-3115-2023
Mathias Vang, Denys Grombacher, Matthew P. Griffiths, Lichao Liu, Jakob Juul Larsen
Abstract. Groundwater is an essential part of the water supply worldwide, and the demands on this water source can be expected to increase in the future. To satisfy the need for resources and to ensure sustainable use of resources, increasingly detailed knowledge of groundwater systems is necessary. However, it is difficult to directly map groundwater with well-established geophysical methods as these are sensitive to both lithology and pore fluid. Surface nuclear magnetic resonance (SNMR) is the only method with a direct sensitivity to water, and it is capable of non-invasively quantifying water content and porosity in the subsurface. Despite these attractive features, SNMR has not been widely adopted in hydrological research, the main reason being an often-poor signal-to-noise ratio, which leads to long acquisition times and high uncertainty in terms of results. Recent advances in SNMR acquisition protocols based on a novel steady-state approach have demonstrated the capability of acquiring high-quality data much faster than previously possible. In turn, this has enabled high-density groundwater mapping with SNMR. We demonstrate the applicability of the new steady-state scheme in three field campaigns in Denmark, where more than 100 SNMR soundings were conducted with a depth of investigation of approximately 30 m. We show how the SNMR soundings enable us to track water level variations at the regional scale, and we demonstrate a high correlation between water levels obtained from SNMR data and water levels measured in boreholes. We also interpret the SNMR results jointly with independent transient electromagnetic (TEM) data, which allows us to identify regions with water bound in small pores. Field practice and SNMR acquisition protocols were optimized during the campaigns, and we now routinely measure high-quality data at 8 to 10 sites per day with a two-person field crew. Together, the results from the three surveys demonstrate that, with steady-state SNMR, it is now possible to map regional variations in water levels with high-quality data and short acquisition times.
{"title":"Technical note: High-density mapping of regional groundwater tables with steady-state surface nuclear magnetic resonance – three Danish case studies","authors":"Mathias Vang, Denys Grombacher, Matthew P. Griffiths, Lichao Liu, Jakob Juul Larsen","doi":"10.5194/hess-27-3115-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3115-2023","url":null,"abstract":"Abstract. Groundwater is an essential part of the water supply worldwide, and the demands on this water source can be expected to increase in the future. To satisfy the need for resources and to ensure sustainable use of resources, increasingly detailed knowledge of groundwater systems is necessary. However, it is difficult to directly map groundwater with well-established geophysical methods as these are sensitive to both lithology and pore fluid. Surface nuclear magnetic resonance (SNMR) is the only method with a direct sensitivity to water, and it is capable of non-invasively quantifying water content and porosity in the subsurface. Despite these attractive features, SNMR has not been widely adopted in hydrological research, the main reason being an often-poor signal-to-noise ratio, which leads to long acquisition times and high uncertainty in terms of results. Recent advances in SNMR acquisition protocols based on a novel steady-state approach have demonstrated the capability of acquiring high-quality data much faster than previously possible. In turn, this has enabled high-density groundwater mapping with SNMR. We demonstrate the applicability of the new steady-state scheme in three field campaigns in Denmark, where more than 100 SNMR soundings were conducted with a depth of investigation of approximately 30 m. We show how the SNMR soundings enable us to track water level variations at the regional scale, and we demonstrate a high correlation between water levels obtained from SNMR data and water levels measured in boreholes. We also interpret the SNMR results jointly with independent transient electromagnetic (TEM) data, which allows us to identify regions with water bound in small pores. Field practice and SNMR acquisition protocols were optimized during the campaigns, and we now routinely measure high-quality data at 8 to 10 sites per day with a two-person field crew. Together, the results from the three surveys demonstrate that, with steady-state SNMR, it is now possible to map regional variations in water levels with high-quality data and short acquisition times.","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135033058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-24DOI: 10.5194/hess-27-3083-2023
Siyuan Wang, M. Hrachowitz, G. Schoups, C. Stumpp
Abstract. Stable isotopes (δ18O) and tritium (3H) are frequently used as tracers in environmental sciences to estimate age distributions of water. However, it has previously been argued that seasonally variable tracers, such as δ18O, generally and systematically fail to detect the tails of water age distributions and therefore substantially underestimate water ages as compared to radioactive tracers such as 3H. In this study for the Neckar River basin in central Europe and based on a >20-year record of hydrological, δ18O and 3H data, we systematically scrutinized the above postulate together with the potential role of spatial aggregation effects in exacerbating the underestimation of water ages. This was done by comparing water age distributions inferred from δ18O and 3H with a total of 21 different model implementations, including time-invariant, lumped-parameter sine-wave (SW) and convolution integral (CO) models as well as StorAge Selection (SAS)-function models (P-SAS) and integrated hydrological models in combination with SAS functions (IM-SAS). We found that, indeed, water ages inferred from δ18O with commonly used SW and CO models are with mean transit times (MTTs) of ∼ 1–2 years substantially lower than those obtained from 3H with the same models, reaching MTTs of ∼10 years. In contrast, several implementations of P-SAS and IM-SAS models not only allowed simultaneous representations of storage variations and streamflow as well as δ18O and 3H stream signals, but water ages inferred from δ18O with these models were, with MTTs of ∼ 11–17 years, also much higher and similar to those inferred from 3H, which suggested MTTs of ∼ 11–13 years. Characterized by similar parameter posterior distributions, in particular for parameters that control water age, P-SAS and IM-SAS model implementations individually constrained with δ18O or 3H observations exhibited only limited differences in the magnitudes of water ages in different parts of the models and in the temporal variability of transit time distributions (TTDs) in response to changing wetness conditions. This suggests that both tracers lead to comparable descriptions of how water is routed through the system. These findings provide evidence that allowed us to reject the hypothesis that δ18O as a tracer generally and systematically “cannot see water older than about 4 years” and that it truncates the corresponding tails in water age distributions, leading to underestimations of water ages. Instead, our results provide evidence for a broad equivalence of δ18O and 3H as age tracers for systems characterized by MTTs of at least 15–20 years. The question to which degree aggregation of spatial heterogeneity can further adversely affect estimates of water ages remains unresolved as the lumped and distributed implementations of the IM-SAS model provided inconclusive results. Overall, this study demonstrates that previously reported underestimations of water ages are most likely not a result of the use of
{"title":"Stable water isotopes and tritium tracers tell the same tale: no evidence for underestimation of catchment transit times inferred by stable isotopes in StorAge Selection (SAS)-function models","authors":"Siyuan Wang, M. Hrachowitz, G. Schoups, C. Stumpp","doi":"10.5194/hess-27-3083-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3083-2023","url":null,"abstract":"Abstract. Stable isotopes (δ18O) and tritium (3H)\u0000are frequently used as tracers in environmental sciences to estimate age\u0000distributions of water. However, it has previously been argued that\u0000seasonally variable tracers, such as δ18O, generally and\u0000systematically fail to detect the tails of water age distributions and\u0000therefore substantially underestimate water ages as compared to radioactive\u0000tracers such as 3H. In this study for the Neckar River basin in\u0000central Europe and based on a >20-year record of hydrological,\u0000δ18O and 3H data, we systematically scrutinized the above\u0000postulate together with the potential role of spatial aggregation effects in\u0000exacerbating the underestimation of water ages. This was done by comparing\u0000water age distributions inferred from δ18O and 3H with a\u0000total of 21 different model implementations, including time-invariant,\u0000lumped-parameter sine-wave (SW) and convolution integral (CO) models as well\u0000as StorAge Selection (SAS)-function models (P-SAS) and integrated hydrological models in\u0000combination with SAS functions (IM-SAS). We found that, indeed, water ages inferred from δ18O with\u0000commonly used SW and CO models are with mean transit times (MTTs) of\u0000∼ 1–2 years substantially lower than those obtained from\u00003H with the same models, reaching MTTs of ∼10 years. In\u0000contrast, several implementations of P-SAS and IM-SAS models not only\u0000allowed simultaneous representations of storage variations and streamflow as\u0000well as δ18O and 3H stream signals, but water ages\u0000inferred from δ18O with these models were, with MTTs of\u0000∼ 11–17 years, also much higher and similar to those inferred\u0000from 3H, which suggested MTTs of ∼ 11–13 years. Characterized by similar parameter posterior distributions, in particular\u0000for parameters that control water age, P-SAS and IM-SAS model\u0000implementations individually constrained with δ18O or 3H\u0000observations exhibited only limited differences in the magnitudes of water\u0000ages in different parts of the models and in the temporal variability of transit time distributions (TTDs) in response to changing wetness conditions. This suggests that both\u0000tracers lead to comparable descriptions of how water is routed through the\u0000system. These findings provide evidence that allowed us to reject the\u0000hypothesis that δ18O as a tracer generally and systematically\u0000“cannot see water older than about 4 years” and that it truncates the\u0000corresponding tails in water age distributions, leading to underestimations\u0000of water ages. Instead, our results provide evidence for a broad equivalence\u0000of δ18O and 3H as age tracers for systems characterized by\u0000MTTs of at least 15–20 years. The question to which degree aggregation of\u0000spatial heterogeneity can further adversely affect estimates of water ages\u0000remains unresolved as the lumped and distributed implementations of the\u0000IM-SAS model provided inconclusive results. Overall, this study demonstrates that previously reported underestimations\u0000of water ages are most likely not a result of the use of ","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44654965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-22DOI: 10.5194/hess-27-3059-2023
D. Rasche, J. Weimar, M. Schrön, M. Köhli, M. Morgner, A. Güntner, T. Blume
Abstract. Above-ground cosmic-ray neutron sensing (CRNS) allows for the non-invasive estimation of the field-scale soil moisture content in the upper decimetres of the soil. However, large parts of the deeper vadose zone remain outside of its observational window. Retrieving soil moisture information from these deeper layers requires extrapolation, modelling or other methods, all of which come with methodological challenges. Against this background, we investigate CRNS for downhole soil moisture measurements in deeper layers of the vadose zone. To render calibration with in situ soil moisture measurements unnecessary, we rescaled neutron intensities observed below the terrain surface with intensities measured above a waterbody. An experimental set-up with a CRNS sensor deployed at different depths of up to 10 m below the surface in a groundwater observation well combined with particle transport simulations revealed the response of downhole thermal neutron intensities to changes in the soil moisture content at the depth of the downhole neutron detector as well as in the layers above it. The simulation results suggest that the sensitive measurement radius of several decimetres, which depends on soil moisture and soil bulk density, exceeds that of a standard active neutron probe (which is only about 30 cm). We derived transfer functions to estimate downhole neutron signals from soil moisture information, and we describe approaches for using these transfer functions in an inverse way to derive soil moisture from the observed neutron signals. The in situ neutron and soil moisture observations confirm the applicability of these functions and prove the concept of passive downhole soil moisture estimation, even at larger depths, using cosmic-ray neutron sensing.
{"title":"A change in perspective: downhole cosmic-ray neutron sensing for the estimation of soil moisture","authors":"D. Rasche, J. Weimar, M. Schrön, M. Köhli, M. Morgner, A. Güntner, T. Blume","doi":"10.5194/hess-27-3059-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3059-2023","url":null,"abstract":"Abstract. Above-ground cosmic-ray neutron sensing (CRNS) allows for the non-invasive estimation of the field-scale soil moisture content in the upper\u0000decimetres of the soil. However, large parts of the deeper vadose zone remain outside of its observational window. Retrieving soil moisture\u0000information from these deeper layers requires extrapolation, modelling or other methods, all of which come with methodological challenges. Against\u0000this background, we investigate CRNS for downhole soil moisture measurements in deeper layers of the vadose zone. To render calibration with in situ\u0000soil moisture measurements unnecessary, we rescaled neutron intensities observed below the terrain surface with intensities measured above a waterbody. An experimental set-up with a CRNS sensor deployed at different depths of up to 10 m below the surface in a groundwater observation well\u0000combined with particle transport simulations revealed the response of downhole thermal neutron intensities to changes in the soil moisture content at\u0000the depth of the downhole neutron detector as well as in the layers above it. The simulation results suggest that the sensitive measurement radius\u0000of several decimetres, which depends on soil moisture and soil bulk density, exceeds that of a standard active neutron probe (which is only about\u000030 cm). We derived transfer functions to estimate downhole neutron signals from soil moisture information, and we describe approaches for\u0000using these transfer functions in an inverse way to derive soil moisture from the observed neutron signals. The in situ neutron and soil moisture\u0000observations confirm the applicability of these functions and prove the concept of passive downhole soil moisture estimation, even at larger depths,\u0000using cosmic-ray neutron sensing.\u0000","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43012899","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-22DOI: 10.5194/hess-27-3021-2023
Stephen K. Adams, Brian P. Bledsoe, Eric D. Stein
Abstract. Environmental streamflow management can improve the ecological health of streams by returning modified flows to more natural conditions. The Ecological Limits of Hydrologic Alteration (ELOHA) framework for developing regional environmental flow criteria has been implemented to reverse hydromodification across the heterogenous region of coastal southern California (So. CA) by focusing on two elements of the flow regime: streamflow permanence and flashiness. Within ELOHA, classification groups streams by hydrologic and geomorphic similarity to stratify flow–ecology relationships. Analogous grouping techniques are used by hydrologic modelers to facilitate streamflow prediction in ungaged basins (PUB) through regionalization. Most watersheds, including those needed for stream classification and environmental flow development, are ungaged. Furthermore, So. CA is a highly heterogeneous region spanning gradients of urbanization and flow permanence, which presents a challenge for regionalizing ungaged basins. In this study, we develop a novel classification technique for PUB modeling that uses an inductive approach to group perennial, intermittent, and ephemeral regional streams by modeled hydrologic similarity followed by deductively determining class membership with hydrologic model errors and watershed metrics. As a new type of classification, this hydrologic-model-based classification (HMC) prioritizes modeling accuracy, which in turn provides a means to improve model predictions in ungaged basins while complementing traditional classifications and improving environmental flow management. HMC is developed by calibrating a regional catalog of process-based rainfall–runoff models, quantifying the hydrologic reciprocity of calibrated parameters that would be unknown in ungaged basins and grouping sites according to hydrologic and physical similarity. HMC was applied to 25 USGS streamflow gages in the “South Coast” region of California and was compared to other hybrid PUB approaches combining inductive and deductive classification. Using an average cluster error metric, results show that HMC provided the most hydrologically similar groups according to calibrated parameter reciprocity. Hydrologic-model-based classification is relatively complex and time-consuming to implement, but it shows potential for simplifying ungaged basin management. This study demonstrates the benefits of thorough stream classification using multiple approaches and suggests that hydrologic-model-based classification has advantages for PUB and building the hydrologic foundation for environmental flow management.
{"title":"Advancing stream classification and hydrologic modeling of ungaged basins for environmental flow management in coastal southern California","authors":"Stephen K. Adams, Brian P. Bledsoe, Eric D. Stein","doi":"10.5194/hess-27-3021-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3021-2023","url":null,"abstract":"Abstract. Environmental streamflow management can improve the ecological health of streams by returning modified flows to more natural conditions. The Ecological Limits of Hydrologic Alteration (ELOHA) framework for developing regional environmental flow criteria has been implemented to reverse hydromodification across the heterogenous region of coastal southern California (So. CA) by focusing on two elements of the flow regime: streamflow permanence and flashiness. Within ELOHA, classification groups streams by hydrologic and geomorphic similarity to stratify flow–ecology relationships. Analogous grouping techniques are used by hydrologic modelers to facilitate streamflow prediction in ungaged basins (PUB) through regionalization. Most watersheds, including those needed for stream classification and environmental flow development, are ungaged. Furthermore, So. CA is a highly heterogeneous region spanning gradients of urbanization and flow permanence, which presents a challenge for regionalizing ungaged basins. In this study, we develop a novel classification technique for PUB modeling that uses an inductive approach to group perennial, intermittent, and ephemeral regional streams by modeled hydrologic similarity followed by deductively determining class membership with hydrologic model errors and watershed metrics. As a new type of classification, this hydrologic-model-based classification (HMC) prioritizes modeling accuracy, which in turn provides a means to improve model predictions in ungaged basins while complementing traditional classifications and improving environmental flow management. HMC is developed by calibrating a regional catalog of process-based rainfall–runoff models, quantifying the hydrologic reciprocity of calibrated parameters that would be unknown in ungaged basins and grouping sites according to hydrologic and physical similarity. HMC was applied to 25 USGS streamflow gages in the “South Coast” region of California and was compared to other hybrid PUB approaches combining inductive and deductive classification. Using an average cluster error metric, results show that HMC provided the most hydrologically similar groups according to calibrated parameter reciprocity. Hydrologic-model-based classification is relatively complex and time-consuming to implement, but it shows potential for simplifying ungaged basin management. This study demonstrates the benefits of thorough stream classification using multiple approaches and suggests that hydrologic-model-based classification has advantages for PUB and building the hydrologic foundation for environmental flow management.","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135670597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-22DOI: 10.5194/hess-27-3041-2023
J. Strüven, S. Hergarten
Abstract. Understanding the properties of preferential flow patterns is a major challenge in subsurface hydrology. Most of the theoretical approaches in this field stem from research on karst aquifers, where two or three distinct flow components with different timescales are typically considered. This study is based on a different concept: a continuous spatial variation in transmissivity and storativity over several orders of magnitude is assumed. The distribution and spatial pattern of these properties are derived from the concept of minimum energy dissipation. While the numerical simulation of such systems is challenging, it is found that a restriction to a dendritic flow pattern, similar to rivers at the surface, works well. It is also shown that spectral theory is useful for investigating the fundamental properties of such aquifers. As a main result, the long-term recession of the spring draining the aquifer during periods of drought becomes slower for large catchments. However, the dependence of the respective recession coefficient on catchment size is much weaker than for homogeneous aquifers. Concerning the short-term behavior after an instantaneous recharge event, strong deviations from the exponential recession of a linear reservoir are observed. In particular, it takes a considerable time span until the spring discharge reaches its peak. The order of magnitude of this rise time is one-seventh of the characteristic time of the aquifer. Despite the strong deviations from the linear reservoir at short time spans, the exponential component typically contributes more than 80 % to the total discharge. This fraction is much higher than expected for karst aquifers and even exceeds the fraction predicted for homogeneous aquifers.
{"title":"Flow recession behavior of preferential subsurface flow patterns with minimum energy dissipation","authors":"J. Strüven, S. Hergarten","doi":"10.5194/hess-27-3041-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3041-2023","url":null,"abstract":"Abstract. Understanding the properties of preferential flow patterns is a major\u0000challenge in subsurface hydrology. Most of the theoretical approaches in this field stem from research on karst aquifers, where two or three distinct flow components with different timescales are typically considered. This study is based on a different concept: a continuous spatial variation in transmissivity and storativity over several orders of magnitude is assumed. The distribution and spatial pattern of these properties are derived from the concept of minimum energy dissipation. While the numerical simulation of such systems is challenging, it is found that a restriction to a dendritic flow pattern, similar to rivers at the surface, works well. It is also shown that spectral theory is useful for investigating the fundamental properties of such aquifers. As a main result, the long-term recession of the spring draining the aquifer during periods of drought becomes slower for large catchments. However, the dependence of the respective recession coefficient on catchment size is much weaker than for homogeneous aquifers. Concerning the short-term behavior after an instantaneous recharge event, strong deviations from the exponential recession of a linear reservoir are observed. In particular, it takes a considerable time span until the spring discharge reaches its peak. The order of magnitude of this rise time is one-seventh of the characteristic time of the aquifer. Despite the strong deviations from the linear reservoir at short time spans, the exponential component typically contributes more than 80 % to the total discharge. This fraction is much higher than expected for karst aquifers and even exceeds the fraction predicted for homogeneous aquifers.\u0000","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48764700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-14DOI: 10.5194/hess-27-3005-2023
G. Zhang, P. Cui, C. Gualtieri, N. A. Bazai, Xueqin Zhang, Zhengtao Zhang
Abstract. Extreme earthquake disturbances to the vegetation of local and regional landscapes could swiftly impair the former hydrologic function, significantly increasing the challenge of predicting threshold behaviors of rainfall–runoff processes as well as the hydrologic system's complexity over time. It is still unclear how alternating catchment hydrologic behaviors under an ongoing large earthquake disruption are mediated by long-term interactions between landslides and vegetation evolution. In a well-known watershed affected by the Wenchuan earthquake, the nonlinear hydrologic behavior is examined using two thresholds with intervening linear segments. A lower rising threshold (THr) value (210.48 mm) observed in post-earthquake local landslide regions exhibited a faster stormflow response rate than that in undisturbed forest and grassland–shrubland regions, easily triggering huge flash-flood disasters. Additionally, an integrated response metric pair (integrated watershed average generation threshold THg−IWA and rising threshold THr−IWA) with areas of disparate land use, ecology, and physiography was proposed and efficiently applied to identify emergent catchment hydrologic behaviors. The interannual variation in the two integrated hydrologic thresholds before and following the earthquake was assessed to detect the temporal nonstationarity in hydrologic extremes and nonlinear runoff response. The year 2011 was an important turning point along the hydrologic disturbance–recovery timescale following the earthquake, as post-earthquake landslide evolution reached a state of extreme heterogeneity in space. At that time, the THr−IWA value decreased by ∼ 9 mm compared with the pre-earthquake level. This is closely related to the fast expansion of landslides, leading to a larger extension of variable source area from the channel to neighboring hillslopes, and faster subsurface stormflow, contributing to flash floods. Finally, we present a conceptual model interpreting how the short- and long-term interactions between earthquake-induced landslides and vegetation affect flood hydrographs at event timescale that generated an increased nonstationary hydrologic behavior. This study expands our current knowledge of threshold-based hydrologic and nonstationary stormflow behaviors in response to abrupt earthquake disturbance for the prediction of future flood regimes.
{"title":"Increased nonstationarity of stormflow threshold behaviors in a forested watershed due to abrupt earthquake disturbance","authors":"G. Zhang, P. Cui, C. Gualtieri, N. A. Bazai, Xueqin Zhang, Zhengtao Zhang","doi":"10.5194/hess-27-3005-2023","DOIUrl":"https://doi.org/10.5194/hess-27-3005-2023","url":null,"abstract":"Abstract. Extreme earthquake disturbances to the vegetation of local and regional\u0000landscapes could swiftly impair the former hydrologic function,\u0000significantly increasing the challenge of predicting threshold behaviors of\u0000rainfall–runoff processes as well as the hydrologic system's complexity over\u0000time. It is still unclear how alternating catchment hydrologic behaviors\u0000under an ongoing large earthquake disruption are mediated by long-term\u0000interactions between landslides and vegetation evolution. In a well-known watershed affected by the Wenchuan\u0000earthquake, the nonlinear hydrologic behavior is examined\u0000using two thresholds with intervening linear segments. A lower rising threshold (THr)\u0000value (210.48 mm) observed in post-earthquake local landslide regions\u0000exhibited a faster stormflow response rate than that in undisturbed\u0000forest and grassland–shrubland regions, easily triggering huge flash-flood\u0000disasters. Additionally, an integrated response metric pair (integrated\u0000watershed average generation threshold THg−IWA and rising threshold THr−IWA) with areas of disparate land use,\u0000ecology, and physiography was proposed and efficiently applied to identify\u0000emergent catchment hydrologic behaviors. The interannual variation in the two\u0000integrated hydrologic thresholds before and following the earthquake was assessed to\u0000detect the temporal nonstationarity in hydrologic extremes and nonlinear\u0000runoff response. The year 2011 was an important turning point along the\u0000hydrologic disturbance–recovery timescale following the earthquake, as\u0000post-earthquake landslide evolution reached a state of extreme\u0000heterogeneity in space. At that time, the THr−IWA value decreased by\u0000∼ 9 mm compared with the pre-earthquake level. This is closely\u0000related to the fast expansion of landslides, leading to a larger extension of\u0000variable source area from the channel to neighboring hillslopes, and faster\u0000subsurface stormflow, contributing to flash floods. Finally, we present a\u0000conceptual model interpreting how the short- and long-term interactions between\u0000earthquake-induced landslides and vegetation affect flood hydrographs at\u0000event timescale that generated an increased nonstationary hydrologic\u0000behavior. This study expands our current knowledge of threshold-based\u0000hydrologic and nonstationary stormflow behaviors in response to abrupt\u0000earthquake disturbance for the prediction of future flood regimes.\u0000","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44423642","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-14DOI: 10.5194/hess-27-2989-2023
Arianna Borriero, Rohini Kumar, Tam V. Nguyen, J. Fleckenstein, S. Lutz
Abstract. Transit time distributions (TTDs) of streamflow are useful descriptors for understanding flow and solute transport in catchments. Catchment-scale TTDs can be modeled using tracer data (e.g. oxygen isotopes, such as δ18O) in inflow and outflows by employing StorAge Selection (SAS) functions. However, tracer data are often sparse in space and time, so they need to be interpolated to increase their spatiotemporal resolution. Moreover, SAS functions can be parameterized with different forms, but there is no general agreement on which one should be used. Both of these aspects induce uncertainty in the simulated TTDs, and the individual uncertainty sources as well as their combined effect have not been fully investigated. This study provides a comprehensive analysis of the TTD uncertainty resulting from 12 model setups obtained by combining different interpolation schemes for δ18O in precipitation and distinct SAS functions. For each model setup, we found behavioral solutions with satisfactory model performance for in-stream δ18O (KGE > 0.55, where KGE refers to the Kling–Gupta efficiency). Differences in KGE values were statistically significant, thereby showing the relevance of the chosen setup for simulating TTDs. We found a large uncertainty in the simulated TTDs, represented by a large range of variability in the 95 % confidence interval of the median transit time, varying at the most by between 259 and 1009 d across all tested setups. Uncertainty in TTDs was mainly associated with the temporal interpolation of δ18O in precipitation, the choice between time-variant and time-invariant SAS functions, flow conditions, and the use of nonspatially interpolated δ18O in precipitation. We discuss the implications of these results for the SAS framework, uncertainty characterization in TTD-based models, and the influence of the uncertainty for water quality and quantity studies.
{"title":"Uncertainty in water transit time estimation with StorAge Selection functions and tracer data interpolation","authors":"Arianna Borriero, Rohini Kumar, Tam V. Nguyen, J. Fleckenstein, S. Lutz","doi":"10.5194/hess-27-2989-2023","DOIUrl":"https://doi.org/10.5194/hess-27-2989-2023","url":null,"abstract":"Abstract. Transit time distributions (TTDs) of streamflow are useful descriptors for understanding flow and solute transport in catchments. Catchment-scale TTDs can be modeled using tracer data (e.g. oxygen isotopes, such as δ18O) in inflow and outflows by employing StorAge Selection (SAS) functions.\u0000However, tracer data are often sparse in space and time, so they need to be interpolated to increase their spatiotemporal resolution. Moreover, SAS functions can be parameterized with different forms, but there is no general agreement on which one should be used. Both of these aspects induce uncertainty in the simulated TTDs, and the individual uncertainty sources as well as their combined effect have not been fully investigated.\u0000This study provides a comprehensive analysis of the TTD uncertainty resulting from 12 model setups obtained by combining different interpolation schemes for δ18O in precipitation and distinct SAS functions.\u0000For each model setup, we found behavioral solutions with satisfactory model performance for in-stream δ18O (KGE > 0.55, where KGE refers to the Kling–Gupta efficiency). Differences in KGE values were statistically significant, thereby showing the relevance of the chosen setup for simulating TTDs.\u0000We found a large uncertainty in the simulated TTDs, represented by a large range of variability in the 95 % confidence interval of the median transit time, varying at the most by between 259 and 1009 d across all tested setups. Uncertainty in TTDs was mainly associated with the temporal interpolation of δ18O in precipitation, the choice between time-variant and time-invariant SAS functions, flow conditions, and the use of nonspatially interpolated δ18O in precipitation.\u0000We discuss the implications of these results for the SAS framework, uncertainty characterization in TTD-based models, and the influence of the uncertainty for water quality and quantity studies.\u0000","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44050033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-11DOI: 10.5194/hess-27-2973-2023
Y. Tramblay, P. Arnaud, G. Artigue, Michel Lang, E. Paquet, L. Neppel, E. Sauquet
Abstract. Floods are a major natural hazard in the Mediterranean region, causing deaths and extensive damages. Recent studies have shown that intense rainfall events are becoming more extreme in this region but, paradoxically, without leading to an increase in the severity of floods. Consequently, it is important to understand how flood events are changing to explain this absence of trends in flood magnitude despite increased rainfall extremes. A database of 98 stations in southern France with an average record of 50 years of daily river discharge data between 1959 and 2021 was considered, together with a high-resolution reanalysis product providing precipitation and simulated soil moisture and a classification of weather patterns associated with rainfall events over France. Flood events, corresponding to an average occurrence of 1 event per year (5317 events in total), were extracted and classified into excess-rainfall, short-rainfall, and long-rainfall event types. Several flood event characteristics have been also analyzed: flood event durations, base flow contribution to floods, runoff coefficient, total and maximum event rainfall, and antecedent soil moisture. The evolution through time of these flood event characteristics and seasonality was analyzed. Results indicated that, in most basins, floods tend to occur earlier during the year, the mean flood date being, on average, advanced by 1 month between 1959–1990 and 1991–2021. This seasonal shift could be attributed to the increased frequency of southern-circulation weather types during spring and summer. An increase in total and extreme-event precipitation has been observed, associated with a decrease of antecedent soil moisture before rainfall events. The majority of flood events are associated with excess rainfall on saturated soils, but their relative proportion is decreasing over time, notably in spring, with a concurrent increased frequency of short rain floods. For most basins there is a positive correlation between antecedent soil moisture and flood event runoff coefficients that is remaining stable over time, with dryer soils producing less runoff and a lower contribution of base flow to floods. In a context of increasing aridity, this relationship is the likely cause of the absence of trends in flood magnitudes observed in this region and the change of event types. These changes in flood characteristics are quite homogeneous over the domain studied, suggesting that they are rather linked to the evolution of the regional climate than to catchment characteristics. Consequently, this study shows that even in the absence of trends, flood properties may change over time, and these changes need to be accounted for when analyzing the long-term evolution of flood hazards.
{"title":"Changes in Mediterranean flood processes and seasonality","authors":"Y. Tramblay, P. Arnaud, G. Artigue, Michel Lang, E. Paquet, L. Neppel, E. Sauquet","doi":"10.5194/hess-27-2973-2023","DOIUrl":"https://doi.org/10.5194/hess-27-2973-2023","url":null,"abstract":"Abstract. Floods are a major natural hazard in the Mediterranean region, causing deaths and extensive damages. Recent studies have shown that intense rainfall\u0000events are becoming more extreme in this region but, paradoxically, without leading to an increase in the severity of floods. Consequently, it is\u0000important to understand how flood events are changing to explain this absence of trends in flood magnitude despite increased rainfall extremes. A\u0000database of 98 stations in southern France with an average record of 50 years of daily river discharge data between 1959 and 2021 was\u0000considered, together with a high-resolution reanalysis product providing precipitation and simulated soil moisture and a classification of weather\u0000patterns associated with rainfall events over France. Flood events, corresponding to an average occurrence of 1 event per year (5317 events in\u0000total), were extracted and classified into excess-rainfall, short-rainfall, and long-rainfall event types. Several flood event characteristics have\u0000been also analyzed: flood event durations, base flow contribution to floods, runoff coefficient, total and maximum event rainfall, and antecedent\u0000soil moisture. The evolution through time of these flood event characteristics and seasonality was analyzed. Results indicated that, in most\u0000basins, floods tend to occur earlier during the year, the mean flood date being, on average, advanced by 1 month between 1959–1990 and\u00001991–2021. This seasonal shift could be attributed to the increased frequency of southern-circulation weather types during spring and summer. An\u0000increase in total and extreme-event precipitation has been observed, associated with a decrease of antecedent soil moisture before rainfall\u0000events. The majority of flood events are associated with excess rainfall on saturated soils, but their relative proportion is decreasing over time,\u0000notably in spring, with a concurrent increased frequency of short rain floods. For most basins there is a positive correlation between antecedent\u0000soil moisture and flood event runoff coefficients that is remaining stable over time, with dryer soils producing less runoff and a lower\u0000contribution of base flow to floods. In a context of increasing aridity, this relationship is the likely cause of the absence of trends in flood\u0000magnitudes observed in this region and the change of event types. These changes in flood characteristics are quite homogeneous over the domain\u0000studied, suggesting that they are rather linked to the evolution of the regional climate than to catchment characteristics. Consequently, this\u0000study shows that even in the absence of trends, flood properties may change over time, and these changes need to be accounted for when analyzing the\u0000long-term evolution of flood hazards.\u0000","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":" ","pages":""},"PeriodicalIF":6.3,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44626956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-08-10DOI: 10.5194/hess-27-2951-2023
Rachel E. Havranek, Kathryn Snell, Sebastian Kopf, Brett Davidheiser-Kroll, Valerie Morris, Bruce Vaughn
Abstract. Soil water isotope datasets are useful for understanding connections between the hydrosphere, atmosphere, biosphere, and geosphere. However, they have been underproduced because of the technical challenges associated with collecting those datasets. Here, we present the results of testing and automation of the Soil Water Isotope Storage System (SWISS). The unique innovation of the SWISS is that we are able to automatically collect water vapor from the critical zone at a regular time interval and then store that water vapor until it can be measured back in a laboratory setting. Through a series of quality assurance and quality control tests, we tested whether the SWISS is resistant to both atmospheric intrusion and leaking in both laboratory and field settings. We assessed the accuracy and precision of the SWISS through a series of experiments in which water vapor of known composition was introduced into the flasks, stored for 14 d, and then measured. From these experiments, after applying an offset correction to report our values relative to Vienna Standard Mean Ocean Water (VSMOW), we assess the precision of the SWISS to be ±0.9 ‰ and ±3.7 ‰ for δ18O and δ2H, respectively. We deployed three SWISS units at three different field sites to demonstrate that the SWISS stores water vapor reliably enough that we are able to differentiate dynamics both between the sites as well within a single soil column. Overall, we demonstrate that the SWISS retains the stable isotope composition of soil water vapor for long enough to allow researchers to address a wide range of ecohydrologic questions.
{"title":"Technical note: Lessons from and best practices for the deployment of the Soil Water Isotope Storage System","authors":"Rachel E. Havranek, Kathryn Snell, Sebastian Kopf, Brett Davidheiser-Kroll, Valerie Morris, Bruce Vaughn","doi":"10.5194/hess-27-2951-2023","DOIUrl":"https://doi.org/10.5194/hess-27-2951-2023","url":null,"abstract":"Abstract. Soil water isotope datasets are useful for understanding connections between the hydrosphere, atmosphere, biosphere, and geosphere. However, they have been underproduced because of the technical challenges associated with collecting those datasets. Here, we present the results of testing and automation of the Soil Water Isotope Storage System (SWISS). The unique innovation of the SWISS is that we are able to automatically collect water vapor from the critical zone at a regular time interval and then store that water vapor until it can be measured back in a laboratory setting. Through a series of quality assurance and quality control tests, we tested whether the SWISS is resistant to both atmospheric intrusion and leaking in both laboratory and field settings. We assessed the accuracy and precision of the SWISS through a series of experiments in which water vapor of known composition was introduced into the flasks, stored for 14 d, and then measured. From these experiments, after applying an offset correction to report our values relative to Vienna Standard Mean Ocean Water (VSMOW), we assess the precision of the SWISS to be ±0.9 ‰ and ±3.7 ‰ for δ18O and δ2H, respectively. We deployed three SWISS units at three different field sites to demonstrate that the SWISS stores water vapor reliably enough that we are able to differentiate dynamics both between the sites as well within a single soil column. Overall, we demonstrate that the SWISS retains the stable isotope composition of soil water vapor for long enough to allow researchers to address a wide range of ecohydrologic questions.","PeriodicalId":13143,"journal":{"name":"Hydrology and Earth System Sciences","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135491743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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