Induced seismicity at wujiangdu reservoir,China: a case induced in the karst area

To date 19 cases of reservoir-induced seismicity have been acknowledged in China and 15 of them are associated with karst. The Wujiangdu case is a typical one induced in the karst area. The dam with a height of 165 m is the highest built in a karst area in China. Seismic activity has been successively induced in five reservoir segments seven months after the impoundment in 1979. A temporary seismic network consisting of 8 stations was set up in one of the segments some 40 km upstream from the dam. The results indicate that epicenters were distributed along the immediate banks, composed of karstified carbonate, and focal depths were only several hundred meters. Most of the focal mechanisms were of thrust and normal faulting. It is suggested that karst may be an important factor in inducing seismicity. It can provide an hydraulic connection to change the saturation and pressure and also weak planes for dislocation to induce seismicity.     

Reservoir-type water source vulnerability assessment: a case study of the Yuqiao Reservoir,China

ABSTRACT

In this study, we developed a method to assess reservoir-type water source vulnerability (WSV) and adapted the method to the Yuqiao Reservoir (in Tianjin in North China). First, we identified the factors that influence reservoir vulnerability and selected suitable indexes for vulnerability assessment. Second, the CRITIC, AHP and integrated weighting methods were applied to quantify the index weight. Third, the information diffusion method was applied to process the index data. Finally, the vulnerability of the Yuqiao Reservoir was assessed, and the results showed that the vulnerability of the Yuqiao Reservoir is high, with social factors (i.e. the road traffic system, automatic management control system, potential menace in evaluation scope, destructive man-made accidents, emergency management plan, and per capita water consumption) being the main reasons.     

Effects of land-use/cover change on hydrological processes using a GIS/RS-based integrated hydrological model: case study of the East River,China

Abstract

An integrated model, combining a surface energy balance system, an LAI-based interception model and a distributed monthly water balance model, was developed to predict hydrological impacts of land-use/land-cover change (LUCC) in the East River basin, China, with the aid of GIS/RS. The integrated model is a distributed model that not only accounts for spatial variations in basin terrain, rainfall and soil moisture, but also considers spatial and temporal variation of vegetation cover and evapotranspiration (ET), in particular, thus providing a powerful tool for investigating the hydrological impact of LUCC. The model was constructed using spatial data on topography, soil types and vegetation characteristics together with time series of precipitation from 170 stations in the basin. The model was calibrated and validated based on river discharge data from three stations in the basin for 21 years. The calibration and validation results suggested that the model is suitable for application in the basin. The results show that ET has a positive relationship with LAI (leaf area index), while runoff has a negative relationship with LAI in the same climatic zone that can be described by the surface energy balance and water balance equation. It was found that deforestation would cause an increase in annual runoff and a decrease in annual ET in southern China. Monthly runoff for different land-cover types was found to be inversely related to ET. Also, for most of the scenarios, and particularly for grassland and cropland, the most significant changes occurred in the rainy season, indicating that deforestation would cause a significant increase in monthly runoff in that season in the East River basin. These results are important for water resources management and environmental change monitoring.

Editor Z.W. Kundzewicz     

Effects of area under‐estimations of sloped mountain terrain on simulated hydrological behaviour: a case study using the ACRU model

Sloped areas calculated from a GIS raster file, such as a digital elevation model, are smaller than the true surface area, because they are projected to a planimetric plane. In mountainous regions this sloped area under‐estimation (SAUE) can have significant consequences on hydrological calculations. A sensitivity analysis is conducted, using the ACRU agro‐hydrological modelling system in a small watershed in Glacier National Park, Montana, USA, to investigate the sensitivity of the SAUE on key elements of the hydrological cycle, including precipitation depth, April snow depth, August soil moisture deficit, actual evapotranspiration depth, and runoff depth. The sensitivity analysis is based on 224 unique combinations of slope, soil and land cover types, elevation with associated precipitation depths, and north and south facing radiation regimes. Results revealed an increasing influence of the SAUE on all hydrological processes with increasing slope steepness. Distinct differences and magnitudes between different land cover types, different elevations, and, in particular, different exposition were quantified. Actual evapotranspiration increases with SAUE, while runoff decreases. April soil water is simulated to decrease with an increase in SAUE. Finally, a comparison of a streamflow simulation of a small and steep alpine watershed with and without consideration of the SAUE is carried out. The sloped area of the small watershed is under‐estimated by 20·9%, and the difference in simulated runoff is 12·3%. When the SAUE was not considered, runoff was simulated to be higher, the associated coefficient of determination was slightly lower, and the slope of the regression line was flatter. Copyright © 2010 John Wiley & Sons, Ltd.     

南亚热带特大型水库浮游植物群落特征及其与环境因子的关系:以新丰江水库为例

为了解亚热带大型深水贫营养水库的浮游植物群落特征及生态现状,2019年9月至2020年8月对新丰江水库的浮游植物群落结构和水体理化指标进行了周年调查.结果 表明,新丰江水库水质达到《地表水环境质量标准》(GB 3838-2002)Ⅰ类标准,综合营养状态指数(TLI(∑))在15～28之间,整体上处于贫营养状态.共检出浮...     

基于走航高频监测的水库冬季水体溶解甲烷浓度分布:以湖北西北口水库为例

水库是大气甲烷(CH4)的重要来源之一,但目前对水库(尤其是河道型水库)中溶解CH_4浓度及释放潜力的空间异质性的认识仍不足.为揭示河道型水库冬季溶解CH_4浓度的分布规律,于2020年1月在湖北宜昌黄柏河流域内西北口水库采用自主研发的新型快速水—气平衡装置(FaRAGE)连接便携式温室气体分析仪,开展了水体溶解CH4浓度的连续走航式监测及断面垂向监测.根据溶解CH4从库尾至库首的浓度变化可以将水库分为3段:距回水末端1 km内为快速降低段,溶解CH4浓度范围为0.117～0.233 μmol/L;1～6 km内为缓慢降低段,CH4浓度范围为0.055～0.117 μmol/L;6～13km范围内为浓度平稳段,CH4浓度范围为0.039～0.080 μmd/L.整体上,水库表层水体溶解CH_4浓度与表层水温、水深及距回水末端的距离呈显著负相关关系(r=-0.77、-0.89、-0.81;P0.01),与叶绿素a浓度、溶解氧浓度呈显著正相关性(r=0.95、0.97;P0.01).基于当月平均风速,采用薄边界层法估算了上述3段区域的DH_4扩散通量,分别为(0.023±0.004)、(0.012±0.003)、(0.007±0.001) mg/(m~2·h).西北口水库在冬季表现为向大气释放CH_4的"源",且由于溶解CH_4浓度分布不均而表现出较强的空间差异性.     

热带水库消落区植物群落物种组成与结构特征——以海南松涛水库为例

消落区是河流、湖泊和水库因阶段性或长期性的水位涨落而反复淹没或出露而形成的一种特殊的季节性湿地.消落区植被在维持水陆生态系统的动态平衡、生物多样性、生态安全及生态服务功能等方面发挥着重要作用.通过样方法调查分析了海南松涛水库消落区植物组成、区系特点以及群落分布特征.结果显示：松涛水库消落区共有维管植物40科101属115种,其中被子植物36科97属111种,蕨类植物4科4属4种.植物区系以热带性为主,外来入侵种较多,且既耐水淹又耐干旱植物众多;群落以草本、灌木植物为主,乔木较少且大多以幼苗形式存在.主要群落类型为以铺地黍（Panicum repens）为优势种的复合群落,个别区域零散分布有美洲蟛蜞菊（Wedelia trilobata）、光荚含羞草（Mimosa sepiaria）、猪屎豆（Crotalaria pallida）、马松子（Melochia corchorifolia）、假臭草（Praxelis clematidea）和铺地黍等单优群落.消落区不同海拔区间群落分布存在明显差异,物种多样性从高到低呈显著递减趋势.研究结果可为松涛水库消落区植被恢复工作提供科学指导.     

热分层对水库水质的季节性影响——以西安黑河水库为例

深水水库作为城市的重要供水水源,通常由于热量在垂向水体上的不均匀分配形成热分层.热分层会阻碍垂向上水体交换引发水质分层现象,在冬季水库发生“翻库”之后,水体混合导致水库的整体水质下降.结合热分层指数可以客观、直接地表达水库热分层的稳定程度.综合水库的气温、水体更新率和水质参数(溶解氧、pH、总磷、氨氮)的年度变化,对陕西黑河水库2008-2010年的热分层状况进行研究.研究表明:水库的热分层形成会直接恶化底部水质尤其会加速底部水体中溶解氧的消耗;热分层的年度变化主要受气温控制,但在特定时期较大的水体更新率可以在一定程度上弱化水体热分层,减缓底部水质恶化.该结果可使水库管理者在水库分层最稳定、水质恶化最严重时期以人工调节水体更新率的方式弱化热分层,为保证水质安全提供参考.     

Quantitative assessment of the impact of climate variability and human activities on runoff changes: a case study in four catchments of the Haihe River basin,China

Quantitative evaluation of the effect of climate variability and human activities on runoff is of great importance for water resources planning and management in terms of maintaining the ecosystem integrity and sustaining the society development. In this paper, hydro‐climatic data from four catchments (i.e. Luanhe River catchment, Chaohe River catchment, Hutuo River catchment and Zhanghe River catchment) in the Haihe River basin from 1957 to 2000 were used to quantitatively attribute the hydrological response (i.e. runoff) to climate change and human activities separately. To separate the attributes, the temporal trends of annual precipitation, potential evapotranspiration (PET) and runoff during 1957–2000 were first explored by the Mann–Kendall test. Despite that only Hutuo River catchment was dominated by a significant negative trend in annual precipitation, all four catchments presented significant negative trend in annual runoff varying from ?0.859 (Chaohe River) to ?1.996 mm a^?1 (Zhanghe River). Change points in 1977 and 1979 are detected by precipitation–runoff double cumulative curves method and Pettitt's test for Zhanghe River and the other three rivers, respectively, and are adopted to divide data set into two study periods as the pre‐change period and post‐change period. Three methods including hydrological model method, hydrological sensitivity analysis method and climate elasticity method were calibrated with the hydro‐climatic data during the pre‐change period. Then, hydrological runoff response to climate variability and human activities was quantitatively evaluated with the help of the three methods and based on the assumption that climate and human activities are the only drivers for streamflow and are independent of each other. Similar estimates of anthropogenic and climatic effects on runoff for catchments considered can be obtained from the three methods. We found that human activities were the main driving factors for the decline in annual runoff in Luanhe River catchment, Chaohe River catchment and Zhanghe River catchment, accounting for over 50% of runoff reduction. However, climate variability should be responsible for the decrease in annual runoff in the Hutuo River catchment. Copyright © 2012 John Wiley & Sons, Ltd.     

Regionalisation of the parameters of the log‐Pearson 3 distribution: a case study for New South Wales,Australia

The index flood method is widely used in regional flood frequency analysis (RFFA) but explicitly relies on the identification of ‘acceptable homogeneous regions’. This paper presents an alternative RFFA method, which is particularly useful when ‘acceptably homogeneous regions’ cannot be identified. The new RFFA method is based on the region of influence (ROI) approach where a ‘local region’ can be formed to estimate statistics at the site of interest. The new method is applied here to regionalize the parameters of the log‐Pearson 3 (LP3) flood probability model using Bayesian generalized least squares (GLS) regression. The ROI approach is used to reduce model error arising from the heterogeneity unaccounted for by the predictor variables in the traditional fixed‐region GLS analysis. A case study was undertaken for 55 catchments located in eastern New South Wales, Australia. The selection of predictor variables was guided by minimizing model error. Using an approach similar to stepwise regression, the best model for the LP3 mean was found to use catchment area and 50‐year, 12‐h rainfall intensity as explanatory variables, whereas the models for the LP3 standard deviation and skewness only had a constant term for the derived ROIs. Diagnostics based on leave‐one‐out cross validation show that the regression model assumptions were not inconsistent with the data and, importantly, no genuine outlier sites were identified. Significantly, the ROI GLS approach produced more accurate and consistent results than a fixed‐region GLS model, highlighting the superior ability of the ROI approach to deal with heterogeneity. This method is particularly applicable to regions that show a high degree of regional heterogeneity. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of land‐use changes on hydrological processes in the middle basin of the Heihe River,northwest China

The effects of land‐use changes on the runoff process in the midstream plain of this arid inland river basin are a key factor in the rational allocation of water resources to the middle and lower reaches. The question is whether and by how much increasingly heavy land use impacts the hydrological processes in such an arid inland river basin. The catchment of the Heihe River, one of the largest inland rivers in the arid region of northwest China, was chosen to investigate the hydrological responses to land‐use change. Flow duration curves were used to detect trends and variations in runoff between the upper and lower reaches. Relationships among precipitation, upstream runoff, and hydrological variables were identified to distinguish the effects of climatic changes and upstream runoff changes on middle and downstream runoff processes. The quantitative relation between midstream cultivated land use and various parameters of downstream runoff processes were analysed using the four periods of land‐use data since 1956. The Volterra numerical function relation of the hydrological non‐linear system response was utilized to develop a multifactor hydrological response simulation model based on the three factors of precipitation, upstream runoff, and cultivated land area. The results showed that, since 1967, the medium‐ and high‐coverage natural grassland area in the midstream region has decreased by 80·1%, and the downstream runoff has declined by 27·32% due to the continuous expansion of the cultivated land area. The contribution of cultivated land expansion to the impact on the annual total runoff is 14–31%, on the annual, spring and winter base flow it is 44–75%, and on spring and winter discharge it is 23–64%. Once the water conservation plan dominated by land‐use structural adjustments is implemented over the next 5 years, the mean annual discharge in the lower reach could increase by 8·98% and the spring discharge by 26·28%. This will significantly alleviate the imbalance between water supply and demand in both its quantity and temporal distribution in the middle and lower reaches. Copyright © 2006 John Wiley & Sons, Ltd.     

Assessment of the impact of spatio‐temporal attributes of wetlands on stream flows using a hydrological modelling framework: a theoretical case study of a watershed under temperate climatic conditions

Wetlands play a significant role on the hydrological cycle, reducing flood peaks through water storage functions and sustaining low flows through slow water release ability. However, their impacts on water resources availability and flood control are mainly driven by wetland type (e.g. isolated wetland—IW—and riparian wetland—RW) and location within a watershed. Consequently, assessing the qualitative and quantitative impact of wetlands on hydrological regimes has become a relevant issue for scientists as well as stakeholders and decision‐makers. In this study, the distributed hydrological model, HYDROTEL, was used to investigate the role and impact of the geographic distribution of isolated and RWs on stream flows of the Becancour River watershed of the St Lawrence Lowlands, Quebec, Canada. The model was set up and calibrated using available datasets (i.e. DEM, soil, wetland distribution, climate, land cover, and hydrometeorological data for the 1969–2010 period). Different wetland theoretical location tests (WTLT) were simulated. Results were used to determine whether stream flow parameters, related to peak flows and low flows, were related to: (i) geographic location of wetlands, (ii) typology of wetlands, and (iii) seasonality. The contribution of a particular wetland was assessed using intrinsic characteristics (e.g. surface area, typology) and extrinsic factors (e.g. location in the watershed landscape and seasonality). Through these investigations, the results suggest, to some extent, that both IWs and RWs impact landscape hydrology. The more IWs are located in the upper part of the watershed, the greater their effect on both on high flow damping and low flow support seems to be. The more RWs are connected to a main stream, the greater their effect is. Our modelling results indicate that local landscape conditions may influence the wetland effect; promoting or limiting their efficiency, and thus their impacts on stream flows depend on a combined effect of wetland and landscape attributes. Copyright © 2015 John Wiley & Sons, Ltd.     

水源水库季节性分层及悬浮物行为对铁锰迁移的影响——以辽宁省碧流河水库为例

铁和锰是氧化还原敏感的元素,水源水库热分层引起的底层水体缺氧造成了沉积物中铁和锰的释放,对城市供水造成了极大的影响.以往鲜有悬浮物行为对铁和锰在水库水-沉积物界面迁移影响的研究,于2014年2月-2015年2月对碧流河水库深水区的水、悬浮物以及沉积物铁和锰的垂向分布特征进行综合调查分析,并进一步分析铁和锰的季节性变化规律及悬浮物行为对其的影响.Spearman相关分析结果表明铁浓度与总悬浮固体、总氮和总磷的相关性较大;锰浓度与总悬浮固体、溶解氧、pH和总氮的相关性较大.进一步讨论分析表明碧流河水库的热分层、底层缺氧以及沉积物再悬浮是影响铁和锰浓度的重要因素,水库铁和锰的季节变化规律存在差异.分层期溶解态的锰在底层累积,平均浓度达到0.18 mg/L,而沉积物中溶解态的铁释放很少.混合期水库的中上层锰浓度升高,达到了0.07 mg/L.沉积物的再悬浮是水库底层水体中铁的主要来源,底层颗粒态铁的平均浓度约为0.3 mg/L.絮凝的颗粒物以及其吸附的锰在水库长期悬浮,难以沉积到水库底部,使得悬浮物中Mn的含量显著高于表层沉积物,约为沉积物的7倍.建议应在碧流河水库采用分层取水、水库曝气以及联合供水等措施,以减少铁和锰的浓度升高对供水产生的影响,保障大连市城市供水安全.     

Effects of the normal operation of the Three Gorges Reservoir on wetland inundation in Dongting Lake,China: a modelling study

Abstract

The operation of the Three Gorges Reservoir (TGR) is an important driver of the recent hydrological changes in the lowlands of Dongting Lake, China. Nevertheless, there has been no convincing study on the quantitative effects of the TGR regulation on the wetland inundation process. Here, the temporal and spatial patterns of the response of wetland inundation in Dongting Lake to the TGR regulation are addressed in detail using a two-dimensional hydrodynamic model, which can accurately reproduce the flooding and drying processes. The results show that temporal patterns of wetland inundation are altered by the TGR regulation, especially in the water pre-releasing period (May to early June) and the water storing period (late September to November). Spatially heterogeneous effects are also observed in Dongting Lake. These findings can help us to take measures at an early stage to effectively deal with the possible adverse effects of the normal operation of the TGR on Dongting Lake.

Editor D. Koutsoyiannis; Associate editor A. Porporato

Citation Lai, X., Jiang, J., and Huang, Q., 2013. Effects of the normal operation of Three Gorges Reservoir on wetland inundation in Dongting Lake, China: a modelling study. Hydrological Sciences Journal, 58 (7), 1467–1477.     

Estimating river discharge from very high‐resolution satellite data: a case study in the Yangtze River,China

The measurement of river discharge is necessary for understanding many water‐related issues. Traditionally, river discharge is estimated by measuring water stage and converting the measurement to discharge by using a stage–discharge rating curve. Our proposed method for the first time couples the measurement of water‐surface width with river width–stage and stage–discharge rating curves by using very high‐resolution satellite data. We used it to estimate the discharge in the Yangtze (Changjiang) River as a case study. The discharges estimated at four stations from five QuickBird‐2 images matched the ground observation data very well, demonstrating that the proposed approach can be regarded as ancillary to traditional field measurement methods or other remote methods to estimate river discharge. Copyright © 2004 John Wiley & Sons, Ltd.     

Combined effect of climate change and human activities on the hydrological processes of an urban river: case study of the Xiaoqing River,China

ABSTRACT

The aim of this study is to reveal statistical characteristics and exceedance probability of discharge under the combined effect of climate change and human activities. The study is conducted in the Xiaoqing River in Jinan, China, based on data of discharge, land-use types and precipitation from the period 1970–2016. A multivariate joint probability distribution of the data is established to test the univariable, bivariable and trivariable change points. These are then used to calculate and analyse the risk probability of discharge exceeding the specific values under different conditions of precipitation and land-use type. The results show that the change point calculated by trivariate joint distribution can reduce the disturbance of the change point obtained with the univariable or bivariable approach and reflect the changes of various factors in the hydrological processes more objectively. When the land-use type is taken into consideration, the trivariate distribution can reflect the variation of hydrological processes more reasonably.     

Interactions between dam‐regulated river flow and riparian groundwater: a case study from the Yellow River,China

The Xiaolangdi Dam, completed in 2000, is second in scale in China to the Three Gorges Project. It has generated remarkable economic and social benefits but with profound impacts to the riverine and regional environments. This paper reports field monitoring of riparian groundwater in the Kouma section of the Yellow River to illustrate the interactions between dam‐regulated river flow and riparian groundwater. The results show that the hydrological condition in riparian zones downstream from the dam has changed from a typical wet–dry cycle to a condition of semi‐permanent dryness, resulting in degradation of the typical attributes and functions of the wetland ecosystem. Hydrological processes in the riparian zone have changed from a complex multiple flooding regime to a simple regime of dominant groundwater drainage towards the river, which only reverses temporarily during the water and sediment regulation period of the dam. Data on groundwater level and groundwater quality show that there are two key points, at ca 200 and 400 m from the river bank, which distinguish zones with different sensitivity to changes of river flow and indicate different interactions between river water and groundwater. The shallow groundwater quality also is negatively affected by the intensive agricultural development that has occurred since the dam was completed. Ecological restoration needs to be carried out to construct a protective natural riparian zone within ca 200 m from the river, this being an ecotone, which is key to the protection of both riparian groundwater and the river. The riparian zone from 200 to 400 m also should be treated as a transitional zone. In addition, ecologically sensitive agriculture and ecotourism organized by local communities would be beneficial in the area beyond 400 m. Copyright © 2011 John Wiley & Sons, Ltd.     

Tributary valley impoundment by trunk river floodplain development: a case study from the KwaZulu‐Natal Drakensberg foothills,eastern South Africa

This paper investigates the origin and geomorphic evolution of Stillerust Vlei, a 189 ha wetland located approximately 150 km northwest of Durban in the temperate submontane foothills of the KwaZulu‐Natal Drakensberg Mountains. The investigation confirms the findings of previous research on the arid to semi‐arid South African interior, which established that many floodplain wetlands in eastern South Africa are located upstream of resistant rock barriers (dolerite intrusions) that cross river courses and form stable local base levels. Upstream of these barriers, rivers laterally plane less resistant Karoo sedimentary rocks (sandstones, mudstones), creating broad, low gradient valleys conducive to the formation of floodplain wetlands. In addition, the study examines how local levee and alluvial ridge accretion on the floodplain of Stillerust Vlei has impounded a small tributary valley, and drawing on observations of similar wetlands in the region, the paper explains the origin and geomorphic evolution of wetlands in floodplain‐abutting valleys, and associated streams that commonly become discontinuous toward their confluence with the trunk (floodplain) river. Controls on the origin and geomorphic evolution of Stillerust Vlei are placed within the context of slope‐channel decoupling and (dis)connectivity in sediment delivery, illustrating that wetlands are environments of deposition. As a result of dynamic trunk‐tributary relations, Stillerust Vlei holds a diversity of geomorphic features, and thus provides potential habitat for a diversity of biota. Copyright © 2008 John Wiley & Sons, Ltd.     

Suitability of CLIGEN precipitation estimates based on an updated database and their impacts on urban runoff: a case study of the Great Lakes Region,USA

ABSTRACT

Weather generators rely on historical meteorological records to simulate time series of synthetic weather sequences, the quality of which has direct influence on model applications. The climate generator CLIGEN’s database has recently been updated to comprise consistent historical records from 1974 to 2013 (updated CLIGEN database, UCD) compared to the current database in which records are of different lengths. In this study, CLIGEN’s performance in estimating precipitation using UCD (eight stations) and the subsequent impact on urban runoff simulations (371 stations) were evaluated in the Great Lakes Region, USA. Generally, UCD-based precipitation could replicate observed daily precipitation up to the 99.5th percentile, but maximum precipitation was underestimated. Results from the Long-Term Hydrologic Impact Assessment model using UCD-based precipitation showed about 0.57 billion cubic meters more (14.9%) average annual runoff being simulated compared with simulations based on the current CLIGEN database. Overall, CLIGEN with the updated database was found suitable for providing precipitation estimates and for use with modeling urban runoff or urbanization effects.     

From mass‐wasting to slope stabilization – putting constrains on a tectonically induced transition in slope erosion mode: a case study in the Judea Hills,Israel

Calcrete‐coated remnants of landslide debris and alluvial deposits are exposed along the presently stable hillslopes of the Soreq drainage, Judea Hills, Israel. These remnants indicate that a transition from landslide‐dominated terrain to dissolution‐controlled hillslope erosion had occurred. This transition possibly occurred due to the significant decrease in tectonic uplift during the late Cenozoic. The study area is characterized by sub‐humid Mediterranean climate. The drainage hillslopes are typically mantled by thick calcrete crusts overlying Upper Cretaceous marine carbonate rocks. Using TT‐OSL dating of aeolian quartz grains incorporated in the calcrete which cements an ancient landslide deposit, we conclude that incision of ~100 m occurred from 1056 ± 262 to 688 ± 86 ka due to ~0·3° westward tilt of the region; such incision invoked high frequency of landslide activity in the drainage. The ages of a younger landslide remnant, alluvial terrace, and alluvial fan, all situated only a few meters above the present level of the active streambed, range between 688 ± 86 ka and 244 ± 25 ka and indicate that since 688 ± 86 the Soreq base level had stabilized and that landslide activity decreased significantly by the middle Pleistocene. Copyright © 2012 John Wiley & Sons, Ltd.