T. Nõges, S. Vilbaste, M. J. McCarthy, Marju Tamm, P. Nõges
We analysed long-term (1992–2020) changes in fertiliser use, wastewater treatment, and river water nutrient status in Estonia (N-E Europe) in the context of changing socio-economic situations and legislation. We hypothesised that more precise regulation of fertiliser usage and improved wastewater treatment are reflected as declining riverine nutrient concentrations, and that the largest relative improvements occurred in catchments with initially high proportions of point source loading. We used data on population and livestock densities, fertiliser use, and wastewater treatment from the Statistics Estonia database and riverine nutrient concentrations from the environmental monitoring database. We clustered the rivers by their catchment properties and analysed trends and step changes in their nutrient status. Point source nutrient loading reductions explained most of the observed decline in riverine nitrogen and phosphorus concentrations, whereas the application of mineral fertilisers has increased, hindering efforts to reach water quality and nutrient load targets set by the EU Water Framework Directive and the Baltic Sea Action Plan. Highest nitrogen concentrations and strongest increasing trends were found in rivers within the nitrate vulnerable zone, indicating violation of the EU Nitrates Directive. To comply with these directives, resource managers must address non-point source nutrient loading from river watersheds.
{"title":"Long-term data reflect nitrogen pollution in Estonian rivers","authors":"T. Nõges, S. Vilbaste, M. J. McCarthy, Marju Tamm, P. Nõges","doi":"10.2166/nh.2022.057","DOIUrl":"https://doi.org/10.2166/nh.2022.057","url":null,"abstract":"\u0000 We analysed long-term (1992–2020) changes in fertiliser use, wastewater treatment, and river water nutrient status in Estonia (N-E Europe) in the context of changing socio-economic situations and legislation. We hypothesised that more precise regulation of fertiliser usage and improved wastewater treatment are reflected as declining riverine nutrient concentrations, and that the largest relative improvements occurred in catchments with initially high proportions of point source loading. We used data on population and livestock densities, fertiliser use, and wastewater treatment from the Statistics Estonia database and riverine nutrient concentrations from the environmental monitoring database. We clustered the rivers by their catchment properties and analysed trends and step changes in their nutrient status. Point source nutrient loading reductions explained most of the observed decline in riverine nitrogen and phosphorus concentrations, whereas the application of mineral fertilisers has increased, hindering efforts to reach water quality and nutrient load targets set by the EU Water Framework Directive and the Baltic Sea Action Plan. Highest nitrogen concentrations and strongest increasing trends were found in rivers within the nitrate vulnerable zone, indicating violation of the EU Nitrates Directive. To comply with these directives, resource managers must address non-point source nutrient loading from river watersheds.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47779045","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ali A. Assani, Ayoub Zeroual, C. Kinnard, Alexandre Roy
This study compares the impacts of climate, agriculture and wetlands on the spatio-temporal variability of seasonal daily minimum flows during the period 1930–2019 in 17 watersheds of southern Quebec (Canada). In terms of spatial variability, correlation analysis revealed that seasonal daily minimum flows were mainly negatively correlated with the agricultural surface area in watersheds in spring, summer and fall. In winter, these flows were positively correlated with the wetland surface area and March temperatures but negatively correlated with snowfall. During all four seasons, spatial variability was characterized by higher daily minimum flow values on the north shore (smaller agricultural surface area and larger wetland surface area) than those on the south shore. As for temporal variability, the application of six tests of the long-term trend analysis showed that most agricultural watersheds are characterized by a significant increase in flows during the four seasons due to the reduction in agricultural area, thus favoring water infiltration, and increased rainfall in summer and fall. On the other hand, the reduction in the snowfall resulted in a reduction in summer daily minimum flows observed in several less agricultural watersheds.
{"title":"Spatial–temporal variability of seasonal daily minimum flows in southern Quebec: synthesis on the impacts of climate, agriculture and wetlands","authors":"Ali A. Assani, Ayoub Zeroual, C. Kinnard, Alexandre Roy","doi":"10.2166/nh.2022.070","DOIUrl":"https://doi.org/10.2166/nh.2022.070","url":null,"abstract":"\u0000 This study compares the impacts of climate, agriculture and wetlands on the spatio-temporal variability of seasonal daily minimum flows during the period 1930–2019 in 17 watersheds of southern Quebec (Canada). In terms of spatial variability, correlation analysis revealed that seasonal daily minimum flows were mainly negatively correlated with the agricultural surface area in watersheds in spring, summer and fall. In winter, these flows were positively correlated with the wetland surface area and March temperatures but negatively correlated with snowfall. During all four seasons, spatial variability was characterized by higher daily minimum flow values on the north shore (smaller agricultural surface area and larger wetland surface area) than those on the south shore. As for temporal variability, the application of six tests of the long-term trend analysis showed that most agricultural watersheds are characterized by a significant increase in flows during the four seasons due to the reduction in agricultural area, thus favoring water infiltration, and increased rainfall in summer and fall. On the other hand, the reduction in the snowfall resulted in a reduction in summer daily minimum flows observed in several less agricultural watersheds.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42936359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Simulating rare widespread hydrological events can be difficult even with the use of modelled data such as the UKCP18 12 km regional climate projections. To generate larger event sets for application in catastrophe modelling, two statistical approaches are highlighted and applied to widespread GB-generated flooding events using a grid-based hydrological model and UKCP18 regional projections. An Empirical Copula method was applied on a national scale, generating over 600,000 events across two time-slices (1980–2010 and 2050–2080). This was compared to model-generated events and showed good matching across time-slices and ensemble members, although lacked some ability to describe the least-rare events. The Empirical Copula was also compared to an implementation of a conditional exceedance model. This model was much more computationally intensive so was restricted to Northwest England but offered the ability to be tuned more finely through choices of marginal distributions. Analysing over 11,000 events, it also matched well with the Empirical Copula and model-generated events but under-represented the smallest events. Both approaches require a broad dataset to draw from but showed reasonable efficacy. For simple statistics, the Empirical Copula shows the potential to be a powerful tool in exploring spatial structure over large regions or at a fine spatial resolution.
{"title":"Spatially coherent statistical simulation of widespread flooding events under climate change","authors":"Adam Griffin, A. Kay, E. Stewart, P. Sayers","doi":"10.2166/nh.2022.069","DOIUrl":"https://doi.org/10.2166/nh.2022.069","url":null,"abstract":"\u0000 Simulating rare widespread hydrological events can be difficult even with the use of modelled data such as the UKCP18 12 km regional climate projections. To generate larger event sets for application in catastrophe modelling, two statistical approaches are highlighted and applied to widespread GB-generated flooding events using a grid-based hydrological model and UKCP18 regional projections. An Empirical Copula method was applied on a national scale, generating over 600,000 events across two time-slices (1980–2010 and 2050–2080). This was compared to model-generated events and showed good matching across time-slices and ensemble members, although lacked some ability to describe the least-rare events. The Empirical Copula was also compared to an implementation of a conditional exceedance model. This model was much more computationally intensive so was restricted to Northwest England but offered the ability to be tuned more finely through choices of marginal distributions. Analysing over 11,000 events, it also matched well with the Empirical Copula and model-generated events but under-represented the smallest events. Both approaches require a broad dataset to draw from but showed reasonable efficacy. For simple statistics, the Empirical Copula shows the potential to be a powerful tool in exploring spatial structure over large regions or at a fine spatial resolution.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43619850","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this study, hydrological responses to climate change and land-cover alteration on future runoff in the Zayandeh-Roud dam upstream watershed were assessed. In this regard, land-use maps in 1996, 2008, 2018, and 2033 were generated using Landsat time-series (TM and OLI), Support-Vector Machine (SVM), and the CA-Markov chain model, for analysing the effects of land-cover alteration on future runoff. Second, the Global Circulation Model (GCM) scenario time-series under RCP 2.6 and RCP 8.5 scenarios were downscaled to evaluate the impacts of climate change on future streamflow. Eventually, the HEC-HMS model was calibrated (1996–2018) for evaluating the impacts of climate and land-use map changes. Results showed that the percentage of the urban area and farmland in 2033 compared to 2018 were expected to grow by 0.1 and 2.39% upstream of the Eskandari station and 0.05 and 0.71% upstream of the Ghale-Shahrokh station, respectively, although the percentage of the barren area was expected to remain almost unchanged in both regions. The future stream flow of Eskandari and Ghale-Shahrokh stations in 2033 was expected to decrease by 57–63 MCM (for RCP 2.6 and RCP 8.5) and 295–403 MCM, respectively, where 68–72% and 79–86% were expected to decrease under climate change scenarios and remains are due to land-cover alteration.
{"title":"Future runoff assessment under climate change and land-cover alteration scenarios: a case study of the Zayandeh-Roud dam upstream watershed","authors":"A. Ahmadi, J. Jalali, Ali Mohammadpour","doi":"10.2166/nh.2022.056","DOIUrl":"https://doi.org/10.2166/nh.2022.056","url":null,"abstract":"\u0000 In this study, hydrological responses to climate change and land-cover alteration on future runoff in the Zayandeh-Roud dam upstream watershed were assessed. In this regard, land-use maps in 1996, 2008, 2018, and 2033 were generated using Landsat time-series (TM and OLI), Support-Vector Machine (SVM), and the CA-Markov chain model, for analysing the effects of land-cover alteration on future runoff. Second, the Global Circulation Model (GCM) scenario time-series under RCP 2.6 and RCP 8.5 scenarios were downscaled to evaluate the impacts of climate change on future streamflow. Eventually, the HEC-HMS model was calibrated (1996–2018) for evaluating the impacts of climate and land-use map changes. Results showed that the percentage of the urban area and farmland in 2033 compared to 2018 were expected to grow by 0.1 and 2.39% upstream of the Eskandari station and 0.05 and 0.71% upstream of the Ghale-Shahrokh station, respectively, although the percentage of the barren area was expected to remain almost unchanged in both regions. The future stream flow of Eskandari and Ghale-Shahrokh stations in 2033 was expected to decrease by 57–63 MCM (for RCP 2.6 and RCP 8.5) and 295–403 MCM, respectively, where 68–72% and 79–86% were expected to decrease under climate change scenarios and remains are due to land-cover alteration.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45930396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Surface and groundwater resource availability depends on precipitation patterns. Climatic change may alter not only future annual totals of precipitation but also its temporal distribution. In regions depending strongly on snow accumulation for steady water supply, this can lead to water constraints. We process climatic projections of precipitation from 19 models of the Climate Model Inter-comparison Project 5 for the Po river, Italy. The study area hosts Italy's most important lakes and reservoirs and is inhabited by 19 million people. The river basin is also known for its productive areas of irrigated agriculture. We apply a Bayesian processor of uncertainty, which we calibrate on a comprehensive set of high-resolution gridded observations. The processor outputs predictive densities of precipitation for selected prognostic time windows. These densities can be used in conjunction with an utility function to estimate potential losses and/or evaluate the benefits of mitigating actions. For the study area, annual precipitation will not change notably in the future for both an optimistic and a pessimistic scenario. The temporal distribution of precipitation will become affected. These potential changes result in considerable strain on storage capacity and water flows needed to satisfy irrigation demand as well as hydroelectric and thermal energy production.
{"title":"Post-processing climate projections of precipitation for the Po river basin: will Italy's North become water-constrained?","authors":"Oleksiy Boyko, P. Reggiani, E. Todini","doi":"10.2166/nh.2022.063","DOIUrl":"https://doi.org/10.2166/nh.2022.063","url":null,"abstract":"\u0000 Surface and groundwater resource availability depends on precipitation patterns. Climatic change may alter not only future annual totals of precipitation but also its temporal distribution. In regions depending strongly on snow accumulation for steady water supply, this can lead to water constraints. We process climatic projections of precipitation from 19 models of the Climate Model Inter-comparison Project 5 for the Po river, Italy. The study area hosts Italy's most important lakes and reservoirs and is inhabited by 19 million people. The river basin is also known for its productive areas of irrigated agriculture. We apply a Bayesian processor of uncertainty, which we calibrate on a comprehensive set of high-resolution gridded observations. The processor outputs predictive densities of precipitation for selected prognostic time windows. These densities can be used in conjunction with an utility function to estimate potential losses and/or evaluate the benefits of mitigating actions. For the study area, annual precipitation will not change notably in the future for both an optimistic and a pessimistic scenario. The temporal distribution of precipitation will become affected. These potential changes result in considerable strain on storage capacity and water flows needed to satisfy irrigation demand as well as hydroelectric and thermal energy production.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48899414","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
New dammed reservoirs are expected to have a significant effect on the regional hydrocycle, but the detailed patterns may not be well understood. Regional climate change is likely to cause soil erosion uncertainty by affecting rainfall erosivity. In the present study, local precipitation and rainfall erosivity were investigated to determine the impounding influence of the Three Gorges Reservoir. Daily erosive precipitation, from 1980 to 2020, was categorized into four intensity levels (light, moderate, heavy, and very heavy), as well as extreme rainfall, to understand their contribution to erosivity. It was found that the impoundment significantly affected local precipitation, with both heavy precipitation and the relative erosivity showing a substantial declining trend (Sen's slope = 2.141, p < 0.05). The Mann–Kendall test indicated an abrupt change point around the year 2002, evidencing the effect of the reservoir impoundment (since 2003). Reservoir impoundment redistributed the intensity levels of erosive precipitation, leading to a 24.3% decrease in the erosivity of heavy precipitation and an 8.2% increase in the moderate category. The unimodal distribution of monthly precipitation was altered to a bimodal distribution with peaks in July and September, resulting in a longer but lower-risky erosion period of high concern. The fluctuations of Rx1day and Rx5day were obviously flattered after impoundment, with a 54.2% peak reduction in relative erosivity on average. Results indicated that heavy rainfall (including extreme rainfall) was reduced, and annual precipitation and erosivity both had a more even seasonal distribution following reservoir impoundment.
预计新坝水库将对区域水循环产生重大影响，但其详细模式可能尚不清楚。区域气候变化可能通过影响降雨侵蚀力而引起土壤侵蚀的不确定性。为了确定三峡库区的蓄水影响，本文研究了局地降水和降雨侵蚀力。将1980 - 2020年的日侵蚀降水分为轻度、中度、重度和极重度四个强度级别，以及极端降雨，以了解它们对侵蚀力的贡献。结果表明，蓄水对局地降水影响显著，强降水和相对侵蚀力均呈现明显下降趋势(Sen’s slope = 2.141, p < 0.05)。Mann-Kendall试验在2002年前后出现突变点，表明水库蓄水的影响(2003年以来)。水库蓄水对侵蚀性降水强度进行了再分配，导致强降水侵蚀力下降24.3%，中等降水侵蚀力增加8.2%。月降水量单峰分布转变为7月和9月高峰的双峰分布，形成了较长但风险较低的高度关注侵蚀期。蓄水后Rx1day和Rx5day的波动幅度明显减小，相对侵蚀力峰值平均降低54.2%。结果表明:水库蓄水后强降水(包括极端降水)减少，年降水量和侵蚀力的季节分布更加均匀;
{"title":"Influence of reservoir impoundment on rainfall erosivity in the Three Gorges Reservoir region of China","authors":"Guang-Zhi Jiang, Jiaorong Lv, Xiu-bin He, Y. Bao","doi":"10.2166/nh.2022.038","DOIUrl":"https://doi.org/10.2166/nh.2022.038","url":null,"abstract":"\u0000 New dammed reservoirs are expected to have a significant effect on the regional hydrocycle, but the detailed patterns may not be well understood. Regional climate change is likely to cause soil erosion uncertainty by affecting rainfall erosivity. In the present study, local precipitation and rainfall erosivity were investigated to determine the impounding influence of the Three Gorges Reservoir. Daily erosive precipitation, from 1980 to 2020, was categorized into four intensity levels (light, moderate, heavy, and very heavy), as well as extreme rainfall, to understand their contribution to erosivity. It was found that the impoundment significantly affected local precipitation, with both heavy precipitation and the relative erosivity showing a substantial declining trend (Sen's slope = 2.141, p < 0.05). The Mann–Kendall test indicated an abrupt change point around the year 2002, evidencing the effect of the reservoir impoundment (since 2003). Reservoir impoundment redistributed the intensity levels of erosive precipitation, leading to a 24.3% decrease in the erosivity of heavy precipitation and an 8.2% increase in the moderate category. The unimodal distribution of monthly precipitation was altered to a bimodal distribution with peaks in July and September, resulting in a longer but lower-risky erosion period of high concern. The fluctuations of Rx1day and Rx5day were obviously flattered after impoundment, with a 54.2% peak reduction in relative erosivity on average. Results indicated that heavy rainfall (including extreme rainfall) was reduced, and annual precipitation and erosivity both had a more even seasonal distribution following reservoir impoundment.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"67904997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Eleonora Forzini, Luigi Piemontese, E. Bresci, Blandine Barthod, Florian Bielser, Marc Sylvestre, N. Adhikari, Nirmal Pun, G. Castelli
Storing runoff during the monsoon season in Himalayan hills is crucial to have enough water to cope with the dry season, especially considering that climate change is changing rainfall intensity and pattern. Traditional Nepalese water ponds, called pokharis, are used to store runoff mainly for cattle rearing and rice fields supplementary irrigation. Local communities are interested in restoring existing pokharis and building new ones to improve their economical and living conditions. Selecting the most suitable locations for pokharis is of crucial importance; however, scarce information is available for large-scale site selection. A comprehensive analysis of multiple relevant parameters for traditional ponds siting can lead to more efficient rainwater collection and provide a useful water resource management tool. In this work, we propose a methodology for pokharis’ best-siting analysis, based on geographic information system (GIS), multi-criteria decision-making (MCDM), and participatory research. To our knowledge, this is the first large-scale best-siting analysis for traditional ponds in Nepal. An area of 0.423 km2 (3.47% of the study area) is classified as highly suitable, with 100% agreement with existing pokharis. Despite the low data resolution, which requires a further field inspection for the final site selection, our results provide reliable guidance for pokharis’ large-scale suitability, supporting water-resilience projects in the area.
{"title":"Identification of suitable sites for traditional pokhari water harvesting in mountain rural communities of the Himalaya","authors":"Eleonora Forzini, Luigi Piemontese, E. Bresci, Blandine Barthod, Florian Bielser, Marc Sylvestre, N. Adhikari, Nirmal Pun, G. Castelli","doi":"10.2166/nh.2022.027","DOIUrl":"https://doi.org/10.2166/nh.2022.027","url":null,"abstract":"\u0000 Storing runoff during the monsoon season in Himalayan hills is crucial to have enough water to cope with the dry season, especially considering that climate change is changing rainfall intensity and pattern. Traditional Nepalese water ponds, called pokharis, are used to store runoff mainly for cattle rearing and rice fields supplementary irrigation. Local communities are interested in restoring existing pokharis and building new ones to improve their economical and living conditions. Selecting the most suitable locations for pokharis is of crucial importance; however, scarce information is available for large-scale site selection. A comprehensive analysis of multiple relevant parameters for traditional ponds siting can lead to more efficient rainwater collection and provide a useful water resource management tool. In this work, we propose a methodology for pokharis’ best-siting analysis, based on geographic information system (GIS), multi-criteria decision-making (MCDM), and participatory research. To our knowledge, this is the first large-scale best-siting analysis for traditional ponds in Nepal. An area of 0.423 km2 (3.47% of the study area) is classified as highly suitable, with 100% agreement with existing pokharis. Despite the low data resolution, which requires a further field inspection for the final site selection, our results provide reliable guidance for pokharis’ large-scale suitability, supporting water-resilience projects in the area.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48870081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Most empirical formulae for the basin concentration time (Tc) and storage coefficient (K) focus on estimating the representative values under the ordinary condition, with their return period being a maximum of 100–200 years. Under more extreme conditions, those parameters should be modified to consider faster velocity conditions. The main objective of this study is to examine the possibility of determining these parameters corresponding to the given peak velocity (vp) at the basin outlet. Two issues are involved in this problem; one is whether Tc can be fully expressed by vp, while the other is whether K is still linearly proportional to Tc under extreme conditions. In this study, these two issues are resolved by the theoretical review of these parameters, as well as an analysis of the rainfall–runoff events collected at the Chungju Dam basin, Korea. It is observed that as vp increases, Tc and K decrease. Their relationship is close to inverse but in linear proportion. That is, strong linear relationships are found among Tc, K, and vp. As a result, the ratio of K to Tc is found to be almost identical, regardless of vp. This ratio at a basin can be assumed as a basin characteristic that is unchanged, regardless of the size of rainfall events.
{"title":"Use of basin outlet velocity to determine the basin concentration time and storage coefficient","authors":"Jinwook Lee, C. Yoo","doi":"10.2166/nh.2022.066","DOIUrl":"https://doi.org/10.2166/nh.2022.066","url":null,"abstract":"\u0000 Most empirical formulae for the basin concentration time (Tc) and storage coefficient (K) focus on estimating the representative values under the ordinary condition, with their return period being a maximum of 100–200 years. Under more extreme conditions, those parameters should be modified to consider faster velocity conditions. The main objective of this study is to examine the possibility of determining these parameters corresponding to the given peak velocity (vp) at the basin outlet. Two issues are involved in this problem; one is whether Tc can be fully expressed by vp, while the other is whether K is still linearly proportional to Tc under extreme conditions. In this study, these two issues are resolved by the theoretical review of these parameters, as well as an analysis of the rainfall–runoff events collected at the Chungju Dam basin, Korea. It is observed that as vp increases, Tc and K decrease. Their relationship is close to inverse but in linear proportion. That is, strong linear relationships are found among Tc, K, and vp. As a result, the ratio of K to Tc is found to be almost identical, regardless of vp. This ratio at a basin can be assumed as a basin characteristic that is unchanged, regardless of the size of rainfall events.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45648396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Understanding the response of soil moisture of different vegetation types to rainfall in karst regions in winter is significant for implementing various ecological restoration projects. However, at present, the related research is mainly focused on non-winter seasons, and only few research exist on winter seasons. Therefore, in this study, four types of vegetation – grassland, arable land, shrubland, and forestland – were selected as sample plots in the Guanling County of southwestern Guizhou, China. The magnitude, time, and speed responses of soil moisture of the vegetation types to rainfall were calculated using the time-series data of soil moisture of different vegetation types. The results showed that the response of soil moisture differed between different vegetation types in winter and non-winter seasons in karst areas. Among the four vegetation types, soil moisture response magnitude to rainfall in grassland and arable land had a similar distribution pattern along different soil depths, whereas, in scrubland and forestland, it decreased gradually along the soil depth. In addition, compared with other vegetation types, for grassland soil moisture, the response magnitude, response duration, and response speed to rainfall are the largest, longest, and fastest, respectively. Our study used quantitative indices to illustrate the response of soil moisture to rainfall for different vegetation types under a humid climate in a mid-subtropical zone on sloped, pure limestone land. The results of this study provide a scientific basis for the implementation of ecological restoration projects in karst areas.
{"title":"Response of the winter soil moisture of different vegetation types to rainfall events in karst slope land","authors":"E. Yuan, Qiuwen Zhou, W. Yan, D. Peng, Yalin Wang","doi":"10.2166/nh.2022.033","DOIUrl":"https://doi.org/10.2166/nh.2022.033","url":null,"abstract":"\u0000 Understanding the response of soil moisture of different vegetation types to rainfall in karst regions in winter is significant for implementing various ecological restoration projects. However, at present, the related research is mainly focused on non-winter seasons, and only few research exist on winter seasons. Therefore, in this study, four types of vegetation – grassland, arable land, shrubland, and forestland – were selected as sample plots in the Guanling County of southwestern Guizhou, China. The magnitude, time, and speed responses of soil moisture of the vegetation types to rainfall were calculated using the time-series data of soil moisture of different vegetation types. The results showed that the response of soil moisture differed between different vegetation types in winter and non-winter seasons in karst areas. Among the four vegetation types, soil moisture response magnitude to rainfall in grassland and arable land had a similar distribution pattern along different soil depths, whereas, in scrubland and forestland, it decreased gradually along the soil depth. In addition, compared with other vegetation types, for grassland soil moisture, the response magnitude, response duration, and response speed to rainfall are the largest, longest, and fastest, respectively. Our study used quantitative indices to illustrate the response of soil moisture to rainfall for different vegetation types under a humid climate in a mid-subtropical zone on sloped, pure limestone land. The results of this study provide a scientific basis for the implementation of ecological restoration projects in karst areas.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41902350","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
T. Kijima, Tsuyoshi Sasagawa, T. Sawaguchi, N. Yamada
Bentonite is an important material for low-permeability engineering systems used in dams and hazardous waste facilities. While models to characterize the hydraulic conductivity of bentonite have been developed in previous studies, these models were not applicable to various density conditions for Na- and Ca-bentonite. In this study, we present a new model for estimating the hydraulic conductivity of bentonite applicable to a wide range of density conditions for Na- and Ca-bentonite. In order to consider flow paths in compacted bentonite, a lamination structure of montmorillonite stacks was assumed. Our hydraulic model discriminated interlayer pores and other pores by applying a method for estimating the probability of connected pores and hydraulic coefficients governed by the plane Poiseuille flow equation. The model was consistent with the lower part of the experimental data investigated in previous studies on the hydraulic conductivity of Na-bentonite and was in good agreement with the data of Ca-bentonite in the range of an effective montmorillonite density (ρem) at 300 kg/m3 ≤ ρem ≤ 1,400 kg/m3 and 600 kg/m3 ≤ ρem, respectively. However, some experimental values on Ca-bentonite under low-density conditions were far higher than the model results in the case where Ca-bentonite forms flow paths of relatively large pores.
{"title":"A model for estimating the hydraulic conductivity of bentonite under various density conditions","authors":"T. Kijima, Tsuyoshi Sasagawa, T. Sawaguchi, N. Yamada","doi":"10.2166/nh.2022.021","DOIUrl":"https://doi.org/10.2166/nh.2022.021","url":null,"abstract":"\u0000 Bentonite is an important material for low-permeability engineering systems used in dams and hazardous waste facilities. While models to characterize the hydraulic conductivity of bentonite have been developed in previous studies, these models were not applicable to various density conditions for Na- and Ca-bentonite. In this study, we present a new model for estimating the hydraulic conductivity of bentonite applicable to a wide range of density conditions for Na- and Ca-bentonite. In order to consider flow paths in compacted bentonite, a lamination structure of montmorillonite stacks was assumed. Our hydraulic model discriminated interlayer pores and other pores by applying a method for estimating the probability of connected pores and hydraulic coefficients governed by the plane Poiseuille flow equation. The model was consistent with the lower part of the experimental data investigated in previous studies on the hydraulic conductivity of Na-bentonite and was in good agreement with the data of Ca-bentonite in the range of an effective montmorillonite density (ρem) at 300 kg/m3 ≤ ρem ≤ 1,400 kg/m3 and 600 kg/m3 ≤ ρem, respectively. However, some experimental values on Ca-bentonite under low-density conditions were far higher than the model results in the case where Ca-bentonite forms flow paths of relatively large pores.","PeriodicalId":55040,"journal":{"name":"Hydrology Research","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2022-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46572839","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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