Double-mass Analysis Research Articles

Attempt to detect maintenance need rain gauge station by double-mass analysis

Attempt to detect maintenance need rain gauge station by double-mass analysis

Analisis Debit Banjir Pada Perencanaan Saluran Drainase Daerah Padangsambian Kelod Ruas Jalan Gunung Salak

ABSTRACT: The Padangsambian Kelod area is one of the densely populated areas. This causes changes in the land use function from rice fields to housing, which reduces water infiltration, causing surface runoff. So that the author needs to calculate the flood discharge and drainage planning in the area. The stages in calculating flood discharge to planning drainage channels include looking for stations that affect, namely Ngurah Rai Station, Sanglah Station, Ship Station, conducting existing drainage channels. After that, calculate the total rainfall and maximum rainfall, which means that the data will be used for further calculations such as the consistency test of the Double Mass Analysis method, calculating the regional average rainfall, testing the selection of distribution, calculating rainfall, design the Log Person Type III method, calculating Rain intensity (Talbot, Sherman, Ishiguro), Calculating distribution suitability test (Smirnov Kolmogorov), Calculating flood discharge analysis (Rational) to dimensional calculations. In the analysis of the flood discharge, the flood discharge plan for the 5 year return period is 0.049 (m3/s)> the existing flood discharge is 0.030 (m3/s) so it is necessary to plan drainage channels in the Padangsambian Kelod area.

Parsing Weather Variability and Wildfire Effects on the Post‐Fire Changes in Daily Stream Flows: A Quantile‐Based Statistical Approach and Its Application

Determining wildland fire impacts on streamflow can be problematic as the hydrology in burned watersheds is influenced by post-fire weather conditions. This study presents a quantile-based analytical framework for assessing fire impacts on low and peak daily flow magnitudes, while accounting for post-fire weather influences. This framework entails (a) the bootstrap method to compute the relative change in the post-fire annual flow and weather statistics, (b) Double Mass analysis to detect if post-fire baseflow and quick flow yield ratios are significantly altered, and (c) a quantile regression method to parse fire effects on flow at a specific quantile. We illustrate the applicability of this analytical framework using 44 western US streams with at least 5% of their watershed area burned. Results indicate that large, high-severity burns in upland watersheds can raise the streamflow magnitude at the 0.05 th and 0.95 th quantiles for at least the five post-fire years. Quantile regression results show that the median fire-related increase in flow for the five post-fire years can be up to 5000% (Standard Error; SE < 2%) at the 0.05 th quantile and 161% (SE < 10%) at the 0.95 th quantile. The fire-related increase in flow was often pronounced at the 0.05 th quantile for streams in the Pacific Northwest and California regions. The difference in fire effects on flow (at both quantiles) across streams was related to post-fire weather, pyrology, physiography, and land cover. The proposed analytical framework can be useful for detecting and quantifying fire effects on the low and peak stream flows in burned watersheds without overlapping disturbances.

Evaluation of the Effects of Pine Management on the Water Yield and Quality in Southern Brazil

ABSTRACT We evaluated the effects of pine (Pinus taeda L.) thinning and clear-cutting on the water yield and quality of three micro-watersheds from southern Brazil using paired- (reference site) and within-site (pre- and post-management periods) comparisons between 2013 and 2016. We inspected for differences in topographic and remote sensing data between the reference site 1 (native forest) and the managed sites 2 (thinning) and 3 (clear-cutting). Double-mass analysis and analysis of covariance (ANCOVA) were used to evaluate rainfall across sites. Using physicochemical data, we calculated the Water Quality Index (WQI) and measured the water yield, detecting anomalous events with wavelet transform. Finally, we verified differences across- and within-sites in median values of yield and WQI using the non-parametric Mann-Whitney test. The results from paired- and within-site comparisons showed that the management practices did not control the water yield and quality of the three studied micro-watersheds. Statistically significant differences in water yield and WQI were observed between the reference site 1 and pine-planted sites only in the pre-management period. Our findings showed slight differences across sites in morphometric parameters of the watersheds. The ANCOVA confirmed the importance of rainfall in controlling the variability of water yield over the thinning and clear-cutting sites.

密云水库上游径流变化趋势及影响因素

PDF HTML阅读 XML下载 导出引用 引用提醒 密云水库上游径流变化趋势及影响因素 DOI: 10.5846/stxb201609301980 作者: 作者单位: 中国科学院生态环境研究中心 城市与区域生态国家重点实验室;中国科学院大学,中交水运规划设计院有限公司,中国科学院生态环境研究中心 城市与区域生态国家重点实验室;中国科学院大学,中国科学院生态环境研究中心 城市与区域生态国家重点实验室;中国科学院大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家水体污染控制与治理科技重大专项（2014ZX07203010） Attribution analysis of changes in runoff in the upstream of the Miyun Reservoir Author: Affiliation: State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Science,Chinese Academy of Science;University of Chinese Academy of Science,CCCC Water Transportation Consultants Co., Ltd,State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Science,Chinese Academy of Science;China;University of Chinese Academy of Science;China,State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Science,Chinese Academy of Science;University of Chinese Academy of Science Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:对径流演变规律的认识和研究是水资源得到有效利用的前提。密云水库是北京市唯一的地表水源地，水库的正常运行对北京市供水安全有重要的意义。2015年9月，南水北调的水开始进入密云水库，对密云水库上游径流量的研究可以使南水北调的水与其相互配合，有效补充密云水库的水资源，研究上游河流的径流变化趋势很有必要。以密云水库白河（张家坟站）和潮河（下会站）水文站1960-2014年的月径流数据为基础，采用年内径流不均匀系数、滑动平均法、Mann-Kendall突变检验法、小波分析方法、双累积径流曲线法分析了密云水库入库径流的年内分配特征和年际变化特征，径流变化周期趋势及降雨和人类活动对径流变化的影响。结果表明：密云水库入流径流量主要分布在7-9月之间，占全年径流量的70%；白河流域年内径流变化较为剧烈。50年来白河与潮河径流量有减少趋势，递减率分别为3.24m3 s-1（10a）-1和1.60m3 s-1（10a）-1。白河流域和潮河流域径流量存在周期为7a的变化特征。利用累积径流曲线分析降雨和人类活动对密云水库上游径流量的影响，结果表明人类活动是影响密云水库径流变化的主要原因，为71.36%-91.39%，其中白河流域受人类活动干扰更为剧烈。 Abstract:Studying the trends and laws of runoff is fundamental to the proper use of water resources. The Miyun Reservoir is the only surface water source in Beijing and is important to Beijing's water supply. In September 2015, water from South-North Water Diversion Project (SNWDP) was added to the reservoir. Therefore, studying the runoff of upstream in Miyun Reservoir is more necessary for the proper management of the reservoir than ever before. As the amount of the water from SNWDP should supplement the runoff of the upstream, to know the trend of the upstream is necessary. Accordingly, the study analyzed the multi-temporal scale changes and abrupt change of the runoff, the influence factors of the runoff of Zhang Jiafen and Xiahui stations from 1960 to 2014. The methods of trend analysis, the moving average method, the Mann-Kendall method, wavelet analysis, the flow duration curve, and the double mass curve were used. The results indicated that the runoff in Miyun Basin mainly concentrated in July to September, accounting for 70% of the annual runoff, and runoff in the Baihe Basin changed more significantly than that of the Chaohe Basin. From 1960 to 2014, the amount of runoff slowly decreased at the rate of 3.24 and 1.60m3 s-1 (10 a)-1 in Baihe and Chahe respectively, and the runoff in Baihe and Chaohe Basin both showed change period of 7a. The results of double mass analysis indicated that the reduction of runoff in Miyun Basin can mainly be attributed to human activities (71.36-91.39%), and the Baihe Basin was disturbed much greater by human activities. 参考文献 相似文献 引证文献

Variable Streamflow Contributions in Nested Subwatersheds of a US Midwestern Urban Watershed

Quantification of runoff is critical to estimate and control water pollution in urban regions, but variation in impervious area and land-use type can complicate the quantification of runoff. We quantified the streamflow contributions of subwatersheds and the historical changes in streamflow in a flood prone urbanizing watershed in US Midwest to guide the establishment of a future pollution-control plan. Streamflow data from five nested hydrological stations enabled accurate estimations of streamflow contribution from five subwatersheds with variable impervious areas (from 0.5% to 26.6%). We corrected the impact of Missouri river backwatering at the most downstream station by comparing its streamflow with an upstream station using double-mass analysis combined with Bernaola-Galvan Heuristic Segmentation approach. We also compared the streamflow of the urbanizing watershed with seven surrounding rural watersheds to estimate the cumulative impact of urbanization on the streamflow regime. The two most urbanized subwatersheds contributed >365 mm streamflow in 2012 with 657 mm precipitation, which was more than fourfold greater than the two least urbanized subwatersheds. Runoff occurred almost exclusively over the most urbanized subwatersheds during the dry period. The frequent floods occurred and the same amount of precipitation produced ~100 mm more streamflow in 2008–2014 than 1967–1980 in the urbanizing watershed; such phenomena did not occur in surrounding rural watersheds. Our approaches provide comprehensive information for planning on runoff control and pollutant reduction in urban watersheds.

Change of annual extreme water levels and correlation with river discharges in the middle-lower Yangtze River: Characteristics and possible affecting factors

As one of the fastest developing regions in China, the middle-lower Yangtze River (MLYR) is vulnerable to floods and droughts. With obtained time series of annual highest water level (HWL), annual lowest water level (LWL) and the corresponding river discharges from three gauging stations in MLYR that covering the period 1987–2011, the current study evaluated the change characteristics of annual extreme water levels and the correlation with river discharges by using the methods of trend test, Mann-Whitney-Pettitt (MWP) test and double mass analysis. Major result indicated a decreasing/increasing trend for annual HWL/LWL of all stations in MLYR during the study period. A change point in 1999 was identified for annual HWL at the Hankou and Datong stations. The year 2006 was found to be the critical year that the relationship between annual extreme water levels and river discharges changed in the MLYR. With contrast to annual LWL in MLYR, further investigation revealed that the change characteristics of annual HWL were highly consistent with regional precipitation in the Yangtze River Basin, while the linkage with Three Gorges Dam (TGD) operation is not strong. Our observation also pointed out that the effect of serious down cutting of the riverbed and the enlargement of the cross-section area during the initial period of TGD operation caused the downward trend of the relationship between annual LWL and river discharge. Whereas, the relatively raised river water level before the flood season due to TGD regulation since 2006 explained for the changing upward trend of the relationship between annual HWL and river discharge.

Sediment control interventions and river flow dynamics: impact on sediment entry into the large canals

AT Marala barrage, two canals, i.e. Marala Ravi Link Canal (MRLC) and Upper Chenab Canal (UCC) off-take from left side of the River Chenab. MRLC has a very old history of experiencing sedimentation issues. Several attempts have been made to counterfoil or minimize this problem in the recent past. Two remarkable measures are the remodeling of MRLC in 2000–2001 (intervention-1) and the shifting of the confluence point of a heavily sediment-laden upstream tributary of the Chenab River by construction of a spur dike in 2004 (intervention-2). This paper investigates the effectiveness of these structural interventions as sedimentation control measures. The baseline period is selected from 1997 to 2000 and the impact is analyzed for two post-intervention time steps, i.e. evaluation period-1 ranging from 2001 to 2004 and evaluation period-2 from 2005 to 2011. Results obtained from double mass analysis revealed that sediment load increased by 33 and 8 % due to intervention-1, while decreased by 12 and 22 % due to intervention-2 in MRLC and UCC, respectively. The results suggest that monsoon floods are mainly responsible for sediment loading in the canals (66 % for UCC and 73 % for MRLC), supported by the finding that effective discharge (1900 m3 s−1) is almost twice the mean annual river discharge. The discharge classes between 900 and 2900 m3 s−1 are mainly responsible for major proportion (89 % in MRLC and 86 % in UCC) of the total sediment load over the 15-year study period. The intervention-1 could not minimize the sediment entry into the canals; rather it aggravated the situation. The intervention-2, however, proved a useful structural measure in this regard.

Key Issues of Data and Data Checking for Hydrological Analyses - Case Study of Rainfall Data in the Attanagalu Oya Basin of Sri Lanka

Inconsistencies and non-homogeneities in the hydrological and meteorological time series could be identified by incorporating statistical tests that detect trends and change points. Inconsistency which reflects systematic errors during recording and the non homogeneity that arises from either natural or man made changes to the gauging environment are both important for adequate time series analysis. It has also been identified that statistical tests together with physical or historical evidence and justifications from metadata need to be incorporated for a very detailed study. A case study was carried out for the rainfall data of Attanagalu Oya basin in the western province of Sri Lanka with a data set consisting of six stations having daily rainfall data for 30 years. According to Pettitt test, a significant change around 1977 & 1985 at Karasnagala and Pasyala could be found. However Pasyala is the most significant station for the change of rainfall pattern, which was confirmed by t-test. Knowledge of Meta data was found very important in order to make necessary corrections to shifts identified through Double Mass Analysis. This paper shows that statistical tests and rational judgements would enable suitable corrections even though it is common to find that most of the hydrological and meteorological data are either flagged for quality or poorly documented.

Analysis of inconsistencies in multi-year gridded quantitative precipitation estimate over complex terrain and its impact on hydrologic modeling

Summary It is common that bias trends of long term precipitation data change over time due to various factors such as gauge relocation and changes in data processing methods. Temporal consistency of this error characteristic of precipitation data is as important as accuracy itself for reliable streamflow prediction with a hydrologic model. The main goal of this paper is to illustrate the detection and adverse effect of inconsistent precipitation data on distributed hydrologic model simulations over a mountainous basin in the Sierra Nevada Mountains of California. We used 1-h 4 km gridded precipitation time series intended for the second phase of the Distributed Model Intercomparison Project (DMIP-2), sponsored by the US National Weather Service (NWS). We present various analyses to investigate the consistency of an hourly gridded precipitation time series from October 1988 through September 2006. First, hourly gridded precipitation data were aggregated into monthly mean areal precipitation totals over the basin and compared with basin average totals derived from the Parameter-Elevation Regressions on Independent Slopes Model (PRISM) monthly values. Second, double mass analysis was preformed on several discrete locations within the basin using both the DMIP-2 gridded precipitation and PRISM data. In addition, we performed a statistical consistency test on the DMIP-2 time series. Both analyses lead to the conclusion that over the entire analysis time period a clear change in bias in the DMIP-2 data occurred in the beginning of 2003. Moreover, it was found that the PRISM data also exhibit some inconsistency. The inconsistency of two elevation zone mean area precipitation (MAP) time series computed from the DMIP-2 gridded precipitation fields was corrected by adjusting hourly values based on the result from double mass analysis. Model simulations using the adjusted MAP data are improved compared to simulations with the inconsistent MAP input data.

LUCC and its impact on run-off yield in the Bai River catchment--upstream of the Miyun Reservoir basin

The Miyun Reservoir is the most important drinking water source for Beijing-the capital of China with a population of more than 16 million. Since the 1980s, the inflow to the reservoir has been decreasing, which seriously threatens the security of water use in Beijing. Our goal was to analyze the impact of land use and cover change (LUCC) on run-off yield in the upstream of the Miyun Reservoir. In this study, the Soil andWater Assessment Tool (SWAT) was used to simulate the impacts of LUCC on the run-off yield in the Bai River catchment-upstream of the Miyun Reservoir basin in northern China. The investigation was conducted using two 6-year historical streamflow records: from 1986 to 1991 and from 2000 to 2005. A split sample procedure was used for model calibration and validation. The data from 1986 to 1988 and from 2000 to 2002 were used for calibration, while those from 1989 to 1991 and from 2003 to 2005 for validation. The SWAT calibration was based on monthly measured discharge at Zhangjiafen station at the catchment outlet from Bai River catchment. Additionally, the influence of LUCC on the surface run-off was distinguished from that of climate change on the surface runoff through SWAT scenarios modeling, the two-way analysis of variance (ANOVA), and the rainfall-run-off double-mass analysis in the Bai River catchment. We found that the SWAT model could be used successfully to accurately simulate run-off yield and different LUCC patterns affecting water quantity in this catchment. During calibraion for the two periods the simulated monthly run-off satisfactorily matched the observed values, with the Nash-Sutcliffe coefficient > 0.9 and 0.7 and a coefficient of determination of 0.9 and 0.65 at the outlet station (Zhangjiafen station), while during validation for the two periods the obtained values were 0.85, 0.65 and 0.9, 0.65, respectively. During the period of 1986-91, both the SWAT scenarios modeling and the analysis of the two-way ANOVA method showed that LUCC and climate change had some impact on run-off, and the impact of climate change was more significant than that of LUCC. Compared with the period during 1986-91, the run-off yield in the period during 2000-05 significantly decreased. The obtained results from the rainfall-run-off double-mass analysis indicate that since 1998 LUCC has had an increasing influence on the run-off, while the response of the run-off to rainfall has been decreasing. Since 1998, the LUCC has been a major driving force for run-off change in Bai River catchment.

Streamflow changes and its influencing factors in the mainstream of the Songhua River basin, Northeast China over the past 50 years

The Songhua River plays a key role in the national development of China, owing to its unique natural condition and resources. Recent changes in the streamflow in the Songhua River are important with regard to local sustainable development and management under the background of global warming and aggravating soil erosion. In order to detect changes in the streamflow, two streamflow series from 1955 to 2004 (observed at the Harbin and Jiamusi stations) in the mainstream of Songhua River basin were obtained, and methods of statistical analysis, wavelet transform, and double mass analysis were employed to analyze the data. Reasons for the changes to the streamflow are discussed with respect to natural and man-made drivers. The results show the following: (1) From 1955 to 2004, the streamflow series present obvious declining trends. (2) The streamflow series followed the pattern of a wet-dry-wet-dry cycle pattern over the past 50 years. In the mainstream of Songhua River, wet years mainly occurred during the periods of 1955-1966 and 1984-1993, while dry years mainly occurred in the 1970s and after 2000. (3) Within the 50-year scale, the streamflow series appeared in the main periods of circa 33-, 13- and 4-year, in which the 33-year periodicity is the strongest. (4) Precipitation and temperature directly influenced the streamflow in the mainstream of the basin. The discharge was positively correlated with the precipitation and negatively correlated with the temperature. In addition, human activity was another important driving factor for streamflow change. (5) In the mainstream of Songhua River basin, the influences on streamflow can be divided into three periods: 1955-1976, 1977-1997, and 1998-2004. In the first period climate change played a dominant role, and during the latter two periods human influences were enhanced significantly.

Consistency analysis of pluviometric information in Galicia (NW Spain)

An important issue in pluviometric data analysis from rain gauges is the verification of their consistency. In general, this attribute is assessed using double-mass curves. This technique compares cumulative monthly rainfall from a gauge with that averaged from meteorological stations located nearby. The aim of this study was to analyze the quality of monthly rainfall data registered in Galicia (NW Spain) in a five year period (2002–2006). Initially, 159 meteorological stations were evaluated; however, 59 gauges were withdrawn because 10% of their data were missing. Double-mass analysis was performed following two procedures: a) data from each gauge were compared to those obtained in the nearby main station and b) data from each site were compared to the average from five nearby gauges, including data from neighboring regions. The second procedure proved to be more reliable. Rainfall data did not show any outlier for the study period. Determination coefficients were greater than 0.95 in all cases. A graphical analysis showed some deviations from the trend lines in certain stations. First, rainfall maps were obtained by inverse distances weighting. Furthermore, a comprehensive geostatistical analysis, centered in the characterization of the structure of rainfall spatial variability, was performed. Differences between two kriging methods, ordinary and kriging with an external drift, were confirmed, considering the later as a more appropriate technique for rainfall interpolation in the region.

Assessing Rainfall Data Homogeneity and Estimating Missing Records in Mākaha Valley, O‘ahu, Hawai‘i

The objectives of this study were to examine records from long-term rain gauges in Mākaha Valley for data homogeneity and to compare methods of estimating missing data. Double mass analysis was used to investigate data homogeneity. Results show that tree growth near one gauge has reduced rainfall catch by 21–25% since 1974. Four methods for estimating missing daily rainfall data were then tested using index gauges selected from a network of 21 active rain gauges. The number of index gauges and their order of selection were varied according to proximity and correlation. Selection by correlation significantly improved the performance of the station average and inverse distance methods for most cases, as well as the normal ratio method for the case when only one gauge is used. The normal ratio method produces the lowest error when two to five index gauges are used; the inverse distance method yields the lowest error when six or seven index gauges are used. Direct substitution produces better accuracy than th...

An investigation of permanent and transient changes in flood distribution and outflows in the Okavango Delta, Botswana

The annual flood cycle in the Okavango Delta is the basis of subsistence of the local population, providing water, arable land and wetland resources. Additionally, it forms the basis of a large tourism industry. Flooding in the Okavango Delta is, however, very variable both at short and long term time scales. Past research suggested the influence of factors such as tectonic activity, sedimentation, vegetation change or human influence on the spatial distribution of floodwaters. Change in the flooding regime at any given site is thus often perceived as an effect of permanent change in the system, and this perception results in unnecessary demands for engineering interventions in the system. However, it is possible that some of the perceived changes in flood regime are apparent transient effects of non-linearity of the system and variation in hydrological inputs. Hydrometric data and satellite-derived flood maps are analysed here using statistical methods (covariance analysis and double mass analysis) to distinguish between temporal and permanent changes in various parts of the Okavango Delta. The analyses reveal that system non-linearity causes the hydrological responses of the Okavango Delta to be non-proportional to the inputs. Periods of one to several consecutive years are present when flood extents and outflows are either considerably higher or lower (flow or flood regimes) than what would be expected considering the magnitude of inflow. Such effects are visible throughout the entire system, or only in some distributaries, and do not, as previously thought, represent permanent change in flood distribution. However, flood regime change that appears to result from a physical change in the system has been detected. This change has a nature of shift in flood distribution between the Thaoge and the Xudum, with the latter receiving more water after 1997 at the expense of the former and causing 2004 re-flooding of Lake Ngami.

Groundwater abstraction impacts on spring flow and base flow in the Hillsborough River Basin, Florida, USA

Groundwater abstraction has resulted in spring flow and groundwater base-flow declines in the Hillsborough River system of central Florida, USA. These declines have resulted in reduction of inflows to the Tampa city reservoir as well as likely adverse environmental effects on riverine and estuarine biota. Causes evaluated for the declines include effects of groundwater development, reduced rainfall, and land alterations. The karstic, heterogeneic nature of the area renders groundwater flow modeling an ineffective method for overall evaluation. Therefore, the evaluation of these declines is accomplished through the systematic use of parametric and nonparametric statistical techniques. These techniques include contingency table analysis, linear regression, Kendall-Theil and Mann-Kendall trend analysis, locally weighted regression, Pearson correlation, Kendall-tau correlation, Spearman correlation, runs test, Student’s t test, and the Kruskall-Wallis test. Data evaluated include groundwater withdrawals, rainfall, base flow, streamflow, stream stage, spring flow, and groundwater levels. Additional methods used include double mass analysis, base flow separation, a low-stage trend analysis, data visualization techniques, and water level change maps. The methodical application of these analyses and techniques to the hydrologic and climatic data yields the conclusion that the primary factor causing the spring flow and base-flow declines is lowered groundwater levels caused by over-abstraction.

Ecohydrology and Environmental Change to Lake Albacutya and Wyperfeld Park in North‐Western Victoria, Australia

AbstractLake Albacutya is a well‐known intermittent lake in north‐western Victoria. The lake is near the termination of the Wimmera River. From time‐to‐time the lake fills and flow passes down Outlet Creek into Wyperfeld National Park. The wetlands associated with the lake have a high biodiversity value and are named in international treaties. This paper examines the hydrologic factors associated with lake filling and flow into Wyperfeld. The lake has filled approximately six times since 1880 and has partially filled on other occasions. Examination of rainfall data from 1875 at Horsham gave no indication of long term rainfall decline, and showed that rainfall at Horsham can be viewed as representative of rainfall in the Wimmera River catchment. However a double‐mass analysis showed that the relationship between the Wimmera River flow and rainfall has varied from 1890 to the present. Examination of data associated with six fillings of Lake Albacutya suggested that filling is a two‐year event requiring at least 550 GL of flow passing Horsham over the two years immediately associated with the flood. A simple model based on rainfall and this threshold reproduced observed characteristics of the data reasonably well. This suggested that the flooding frequency of Lake Albacutya has dropped from about one in 25 years in the natural state to a substantially lower frequency under current river conditions. The results also suggested that because of changes in the Wimmera River the last filling and flood into Wyperfeld in 1976 was far smaller than it would otherwise have been. This is consistent with field mapping of the flood in relation to River Red Gum (Eucalyptus camaldulensis Dehnh.) stands. Analysis of the health of these stands showed major dieback with the severity of this being roughly proportional to the distance from the 1976 flood boundaries. An examination of values associated with the lake and adjoining Wyperfeld National Park suggested that biodiversity and economic values are and will be compromised by the reduction in flooding. In particular, an internationally‐known provenance of Red Gum is at risk, and bird‐breeding opportunities have diminished.

Summer flows in experimental catchments with different forest covers, Chile

Runoff and peak flows in four experimental catchments with different land uses are analyzed for summer periods. The catchments have a rainy temperate climate with annual precipitations between 2000 and 2500 mm, 70% of which is concentrated in the winter period between May and August. The final harvest of the forest plantation in one of these catchments generated increases in summer runoff. Also, differences between the maximum instantaneous discharge and the flow at the beginning of the storm then almost duplicated those registered in rainfall events of similar magnitude when the catchment was fully forested. Runoff analysis in this catchment is difficult because the two post-harvesting summer periods are much wetter than the two pre-harvesting ones but a double mass analysis shows the effect of harvesting clearly. In a paired catchment study, low cover in one of the two neighbour catchments explains higher direct runoff and base flows although lower maximum instantaneous specific discharge occurred in the less vegetated but larger catchment. Low vegetation cover explains increases in summer flows, although the size, topography, rainfall conditions, road density, extent of affected area and runoff generation processes play an important role in the hydrological effects of different land uses.

Multivariate analysis in hydrology: the factor correspondence analysis method applied to annual rainfall data

Most research on hydrology in developed countries does not emphasize problems that are often encountered by hydrologists in developing countries, problems such as the scarcity and poor quality of data. In developing countries the available data base is often a major constraint and a limiting factor in any hydrological study. This paper analyses the consistency of a network of nonrecording raingauges based on the annual rainfall recorded by six representative stations in the Tacuarembô River basin in Uruguay. The identification of possible errors not revealed in the printed records was accomplished by application of the factor correspondence analysis method and verified with success by the classical double-mass analysis. This ability to identify suspicious data with very modest requirements for data management implies that the methodology based on factor correspondence analysis could find wide application.

Ridge Regression-Time Extrapolation Applied to Hawaiian Rainfall Normals

Abstract In this paper ridge regression is introduced as a technique for extrapolating long-period normal rainfalls from short records. The data used are the annual totals for selected stations on the island of Oahu, Hawaii. It has been shown that when the predictor variables are not mutually independent, as is often the case in meteorology, it is unlikely that the estimates of the coefficients obtained through unbiased multiple linear regression will be close to the correct values. In such cases a method of biased estimation, such as the so-called ridge regression, will yield more accurate estimates of the true regression coefficients. Ridge regression is shown to be superior to ordinary least-squares regression and double-mass analysis, and is a robust estimator of central tendency for extrapolating Hawaiian rainfall normals. Mention is also made on the choice of normal statistic and on the selection of the base period of record. Since there is such a diversity of both topographic and climatological reg...