2016年青海门源MS6.4地震前重力变化

利用青藏高原东北缘2011-2015年期间的流动重力观测资料,系统分析了区域重力场变化及其与2016年1月21日青海门源M_S6.4地震发生的关系,结合GNSS、水准观测成果和区域地质构造动力环境,进一步研究了区域重力场变化的时空分布特征及其机理.结果表明：（1）测区内重力场异常变化与祁连山断裂带在空间上关系密切,反映沿祁连山断裂带（段）在2011-2015年期间发生了引起地表重力变化效应的构造活动或变形.（2）门源M_S6.4地震前,测区内先出现了较大空间范围的区域性重力异常,到临近发震前显示出相对闭锁的现象,且围绕震中区周围出现四象限分布特征的局部重力变化,地震发生在重力反向变化过程中,并出现显著的四象限分布特征的重力异常变化,其中,青海门源与甘肃天祝一带重力差异变化达100×10^-8m·s^-2以上.（3）区域重力场动态演化大体反映了青藏高原东北缘物质北东流的动态效应,门源震中附近区域地壳受挤压变形显著、面压缩率和重力剧烈变化的特征最为显著.（4）重力场的空间分布及其随时间变化与地壳垂直与水平运动及地质构造活动等观测结果有一定的对应关系,强震易发生在重力变化四象限分布中心地带或正、负异常区过渡的高梯度带上.     

2022年门源MS6.9地震震区三维速度与发震机制研究

2022年1月8日,青海省门源县发生M_S6.9地震。使用青海、甘肃等区域数字台网所观测到的2009年1月1日—2022年2月8日间青海门源及周边地区(36°～39°N,101°～104°E)14 869次地震事件的地震观测资料,基于双差成像(TomoDD)方法进行重定位分析,结果表明：门源及周边地区地震震源深度较浅,主要集中在5～15 km深度范围,其中10 km附近分布最多。推断该深度区域为门源及周边地区的主要孕震区。基于地震重定位结果和主震区三维速度结构分别对2016年门源M_S6.4地震和此次地震序列的发震机理进行分析对比,发现两次地震都位于高速异常体边缘,速度结构与断裂、地震序列吻合较好。2022年门源地震位于高速体的西端末梢位置,是该高速体受青藏高原东北缘顺时针应力作用导致的滑动产生的走滑型地震。     

GRACE detection of the medium- to far-field coseismic gravity changes caused by the 2004 MW9.3 Sumatra-Andaman earthquake

Large earthquakes cause observable changes in the Earth's gravity field, which have been detected by the Gravity Recovery and Climate Experiment (GRACE). Since most previous studies focus on the detection of near-field gravity effects, this study provides the results from the medium- to far-field gravity changes caused by the 2004 Sumatra-Andaman earthquake that are recorded within GRACE monthly solutions. Utilizing a spherical-earth dislocation model we documented that large-scale signals predominate in the global field of the coseismic gravity changes caused by the earthquake. After removing the near-field effects, the coseismic gravity changes show a negative anomaly feature with an average magnitude of -0.18×10^-8 m·s^-2 in the region ranging ~40° from the epicenter, which is considered as the "medium field" in this study. From the GRACE data released by Center for Space Research from August 2002 to December 2008, we retrieved the large-scale gravity changes smoothed with 3 000 km Gaussian filter. The results show that the coseismic gravity changes detected by GRACE in the medium field have an average of (-0.20€±0.06)×10^-8 m·s^-2, which agrees with the model prediction. The detection confirms that GRACE is sensitive to large-scale medium-field coseismic gravitational effects of mega earthquakes, and also validates the spherical-earth dislocation model in the medium field from the perspective of satellite gravimetry.     

Volcano-seismic crisis in Montserrat,West Indies, 1966–67

The Soufriere Hills volcano in the south-eastern part of Montserrat erupted pyroclast flows as recently as A. D. 1646 ± 54 years and must therefore be considered dormant, not extinct. The highly destructive nature of pyroclast flow eruptions makes it imperative that such activity should be predicted and, if the threat of eruption becomes sufficiently large, the population should be moved to a sale distance from the volcano. Sharp increases in seismic and solfataric activity occurred in 1966 and these events indicated the abnormally high risk of an eruption in the near future. A network of four short period seismographs was established in the island in May 1966 and between this date and the end of 1967, 723 local earthquakes were recorded, of which 32 were reported felt in the island. Hypocentres were determined for 189 of these earthquakes, and most of these lay in a WNW to ESE belt beneath the Soufriere Hills, at depths of less than 15 km. The average rate of seismic energy release decreased with time throughout the series but there was a strong seasonal variation with maxima in May and November–December of each year. The average depth of the earthquakes decreased from 5.2 km in April and May 1966 to a minimum of 2.8 km from July to September 1966. After September the mean focal depths increased again and by the end of the crisis in November 1967 the mean depth was 9.7 km. Measurements carried out using water-tube tiltmeters showed that the region 2–3 km south-east of the Soufriere Hills was doming upwards until January 1967, then subsided between January–March 1967 and finally rose again at a slower rate between March and September 1967. Heat flow from Galway’s Soufriere which was 3 × 10⁵ cal/sec in 1954 increased to a maximum of 2 × 10⁵ cal/sec in October 1966, then declined to 5 × 10⁵ cal/sec in September 1967. The earthquake series was not the aftershock sequence of any major tectonic earthquake, and only two hypocentres were determined at depths greater than 15 km. It is concluded that magma was intruded into the upper crust beneath the Soufriere Hills volcano and that the earthquakes and other phenomena resulted from the upward migration of this magma.     

2022年1月8日青海门源MS6.9地震GNSS同震形变场及其断层滑动分布

2022年1月8日在青海省海北州门源县发生M_S6.9地震,本次地震是继2016年门源M_S6.4地震后冷龙岭断裂周边发生的又一次强震。确定本次地震的破裂分布对分析该地区震害风险具有重要意义。通过收集震中及周边12个GNSS连续站点和震后加密观测的17个流动站点观测资料,获取了震中100 km范围内29个测站的GNSS静态同震形变场,并以此为约束反演了本次地震同震滑动分布。结果显示,近场GNSS观测到的最大形变量可达1.3 m。反演的最优破裂模型显示该地震主破裂区深度位于0～10 km,滑动破裂出露地表,最大滑动量为4.07 m,地震矩释放能量约1.1×10¹⁹ N·m,对应矩震级M_W6.7。门源地震破裂至地表是造成该地区基础设施破坏的直接原因。     

Crustal structure beneath the eastern part of the Coast Ranges (Diablo Range) of central California from explosion seismic and near earthquake data

Seismic refraction and near earthquake data of the U.S. Geological Survey for central California have been compiled into record sections along profiles and interpreted in terms of crustal structure. The profiles are located northeast of the San Andreas fault of central California and run parallel to the general structures. For the explosion seismic line through the centre of the Diablo Range, an uppermost layer (Franciscan formation) with P velocities of 3.6–5.0 km s^?1 decreases in thickness towards the northwest. The lower boundaries of layers with constant velocities of 5.75 and 6.8 km s^?1 are found at almost constant depths of 12 and 21 km, respectively. Between 21 and 26 km depth a well-defined low-velocity zone appears whose velocity is estimated as ～ 5.3 km s^?1 with the aid of a hedgehog inversion and the calculation of amplitudes. This zone is underlain by a layer 3–5 km thick with a velocity of 7.6 km s^?1. The upper-mantle velocity beneath the Moho at 29–30 km depth is 8.2 km s^?1. The near earthquake profiles, located ～ 20 km southwest and parallel to the explosion seismic line, follow more or less the Hayward and Calaveras fault systems. The velocity-depth distribution derived for the earthquake data is very similar to that found beneath the Diablo Range. However, the low-velocity zone at 21–26 km depth does not seem to exist everywhere along the line. The Moho is not disturbed beneath the Calaveras, Hayward and Silver Creek faults; it rises slightly from the Diablo Range towards the southwest.     

23 October 2011 Van, Eastern Anatolia, earthquake (M W 7.1) and seismotectonics of Lake Van area

The 23 October 2011 Van earthquake took place in the NE part of Lake Van area, surprisingly on a fault (the Van fault) that is not present in the current active fault map of Turkey. However, occurrence of such a large magnitude earthquake in the area is not surprising regarding the historical seismicity of the region. The comparison of the damage patterns suggests that the earthquake is much likely a recurrence of the 1715 Van earthquake. The finite fault modelling of the earthquake using teleseismic broadband body waveforms has shown that the earthquake rupture was unilateral toward SW, was mostly reverse faulting, confined to below the depth of 5 km, did not propagate offshore, and was dominated by a failure of a single asperity with a peak slip of about 5.5 m. The total seismic moment calculated for the model is 4.6?×?10¹⁹ Nm (M _W ?≈?7.1). The finite fault model coincides with the field observations indicating blind faulting and the vertical displacements over the free surface estimated from it correlate well with the maximum reported uplift along the coast of Lake Van above the hanging wall. The possible offshore continuations of the Van fault and some other faults lying its south are also discussed by assessing a previous offshore seismic reflection study and the earthquake epicentres and focal mechanisms.     

The April 24, 2013 Changning M s4.8 earthquake: a felt earthquake that occurred in Paleozoic sediment

The dense broadband seismic network provides more high-quality waveform that is helpful to improve constraint focal depth of shallow earthquake. Many shallow earthquakes occurring in sediment were regarded as induced events. In Sichuan basin, gas industry and salt mining are dependent on fluid injection technique that triggers microseismicity. We adopted waveform inversion method with regional records to obtain focal mechanism of an M _s4.8 earthquake at Changning. The result suggested that the Changning earthquake occurred at a ESE thrust fault, and its focal depth was about 3 km. The depth phases including teleseismic pP phase and regional sPL phase shows that the focal depth is about 2 km. The strong, short-period surface wave suggests that this event is a very shallow earthquake. The amplitude ratio between Rayleigh wave and direct S wave was also used to estimate the source depth of the mainshock. The focal depth (2–4 km) is far less than the depth of the sedimentary layer thickness (6–8 km) in epicentral region. It is close to the depth of fluid injection of salt mining, which may imply that this event was triggered by the industrial activity.     

The mechanism of regional gravity changes before and after the Tangshan earthquake

ＴｈｅｍｅｃｈａｎｉｓｍｏｆｒｅｇｉｏｎａｌｇｒａｖｉｔｙｃｈａｎｇｅｓｂｅｆｏｒｅａｎｄａｆｔｅｒｔｈｅＴａｎｇｓｈａｎｅａｒｔｈｑｕａｋｅＲＵＩ－ＨＡＯＬＩ（李瑞浩）ＪＩＡＮ－ＬＩＡＮＧＨＵＡＮＧ（黄建梁）ＨＵＩＬＩ（李辉）ＤＯＮＧ－ＳＨＥＮＧ...     

Nutrient fluxes induced by disturbance in Meiliang Bay of Lake Taihu

A wave flume experiment was conducted to study nutrient fluxes at water-sediment interface of Meiliang Bay under different hydrodynamic conditions. The results reveal that hydrodynamics has remarkable effects on nutrient fluxes in this area. With a bottom wave stress of 0.019 N m^?2 (equivalent to disturbance caused by wind SE 5–7 m s^?1 at the sediment sample site of Meiliang Bay), the fluxes of TN, TDN and NH₄ ⁺-N were separately 1.92 × 10^?3, ?1.81 × 10^?4 and 5.28 × 10^?4 mg m^?2 s^?1 (positive for upward and negative for downward), but for TP, TDP and SRP, the fluxes were 5.69 × 10^?4, 1.68 × 10^?4 and ?1.29 × 10^?4 mg m^?2 s^?1. In order to calculate the released amount of nutrients based on these results, statistic analysis on the long-term meteorological data was conducted. The result shows that the maximum lasting time for wind SE 5–7 m s^?1 in this area is about 15 h in summer. Further calculation shows that 111 t TN, 32 t NH₄ ⁺-N, 34 t TP and 10 t TDP can be released into water (the sediment area was 47.45% of the whole surface area), resulting in concentration increase of 0.025, 0.007, 0.007 and 0.002 mg L^?1 separately. With stronger disturbance (bottom wave stress is 0.217 N m^?2 which is equivalent to disturbance caused by wind SE 10–11 m s^?1 at the same site), there has been significant increase of nutrient fluxes (1.16 × 10^?2, 6.76 × 10^?3, 1.14 × 10^?2 and 2.14 × 10^?3 mg m^?2 s^?1 for TN, DTN and NH₄ ⁺-N and TP). The exceptions were TDP with flux having a decrease (measured to be 9.54 × 10^?5 mg m^?2 s^?1) and SRP with flux having a small increase (measured to be 5.42 × 10^?5 mg m^?2 s^?1). The same statistic analysis on meteorological data reveal that the maximum lasting time for wind SE 10–11 m s^?1 is no more than 5 h. Based on the nutrient fluxes and the wind lasting-time, similar calculations were also made suggesting that 232 t TN, 134.9 t TDN, 228 t NH₄ ⁺-N, 42.7 t TP, 2.0 t TDP and 1.1 t SRP will be released from sediment at this hydrodynamic condition resulting in the concentration increases of 0.050, 0.029, 0.049, 0.009, 0.0004 and 0.0002 mg L^?1. Therefore in shallow lakes, surface disturbance can lead to significant increase of nutrient concentrations although some components in water column had negative flux with weak disturbance (e.g. TDN and SRP in this experiment). In this case, sediment looks to be a source of nutrients. These nutrients deposited in sediment can be carried or released into water with sediment resuspension or changes of environmental conditions at water-sediment interface, which can have great effects on aquatic ecosystem and is also the characteristics of shallow lakes.     

Accurate Establishment of Error Models for the Satellite Gravity Gradiometry Recovery and Requirements Analysis for the Future GOCE Follow-On Mission

Firstly, the new single and combined error models applied to estimate the cumulative geoid height error are efficiently produced by the dominating error sources consisting of the gravity gradient of the satellite-equipped gradiometer and the orbital position of the space-borne GPS/GLONASS receiver using the power spectral principle. At degree 250, the cumulative geoid height error is 1.769 × 10^?1 m based on the new combined error model, which preferably accords with a recovery accuracy of 1.760 ×10^?1 m from the GOCE-only Earth gravity field model GO_CONS_GCF_2_TIM_R2 released in Germany. Therefore, the new combined error model of the cumulative geoid height is correct and reliable in this study. Secondly, the requirements analysis for the future GOCE Follow-On satellite system is carried out in respect of the preferred design of the matching measurement accuracy of key payloads comprising the gravity gradient and orbital position and the optimal selection of the orbital altitude of the satellite. We recommend the gravity gradient with an accuracy of 10^?13?10^?15 /s², the orbital position with a precision of 1-0.1 cm and the orbital altitude of 200-250 km in the future GOCE Follow-On mission.     

The Beni Haoua,Algeria, Mw 4.9 earthquake: source parameters,engineering, and seismotectonic implications

A moderate Mw 4.9 earthquake struck the Beni Haoua (Algeria) coastal area on April 25, 2012. The mainshock was largely recorded by the accelerograph network of the Centre National de Recherche Appliquée en Génie Parasismique (CGS). The same day the earthquake occurred, eight mobile short period stations were deployed through the epicentral area. In this study, we use accelerogram and seismogram data recorded by these two networks. We combined the focal mechanism built from the first motion of P waves and from waveform inversion, and the distribution of aftershocks to well constrain the source parameters. The mainshock is located with a shallow focal depth, ～9 km, and the focal mechanism shows a nearly pure left lateral strike slip motion, with total seismic moment of 2.8?×?10¹⁶ N.m (M_w?=?4.9). The aftershocks mainly cluster on a narrow NS strip, starting at the coast up to 3–4 km inland. This cluster, almost vertical, is concentrated between 6 and 10 km depth. The second part of this work concerns the damage distribution and estimated intensity in the epicentral area. The damage distribution is discussed in connection with the observed maximum strong motion. The acceleration response spectrum with 5 % damping of the mainshock and aftershocks give the maximum amplitude in high frequency which directly affects the performance of the high-frequency structures. Finally, we tie this earthquake with the seismotectonic of the region, leading to conclude that it occurred on a N–S transform zone between two major compressional fault zones oriented NE–SW.     

2016年1月21日青海门源6.4级地震的发震机制探讨

2016年01月21日青海省门源县发生6.4级地震,地震现场考察的震害分布椭圆长轴走向120°N—140°E.震后0.8 m高分遥感影像与震前高分影像的对比解译结果表明,本次地震导致大于23处较集中的崩塌滑坡,它们的空间分布表现出震中北侧多于南侧,分布点总体形态呈NNW向延展的平面特征.区域断裂几何展布和活动性质的高分遥感解译和野外考察研究表明,冷龙岭断裂水平运动分量占绝对优势,如果本次地震发生在该断裂上,不应为纯逆冲性质.震中区域活动断裂的精细研究发现在冷龙岭北侧发育一条走向约为140°的活动断裂,该断裂在高分影像上地表为北倾,该断裂与多家机构的震源机制解节面Ⅰ走向非常相近.本次地震的余震分布总体长轴方向与冷龙岭断裂相差约20°,而与最新发现的冷龙岭北侧断裂走向相近.综合以上多方面资料,认为冷龙岭北侧断裂极有可能是本次地震的发震断裂.综合余震分布在深部的展布特征,主震的震源机制解,发震断裂在地表的几何展布特征和活动性质,再结合震区附近大地电磁测深等地球物理资料,建立了发震机制模型,认为本次地震是2008年于田7.4级地震、2014年于田7.3级地震后,青藏高原块体向北东方向推挤生长过程中发生的一次地震事件.     

Simultaneous water and vapour transfer in an unsaturated mudstone in badlands terrain,southwestern Taiwan

The simultaneous transfer of pore fluid and vapour was studied in the unsaturated shallow subsurface of a Plio-Pleistocene marine mudstone badland slope in southwestern Taiwan during the dry season using field monitoring data and numerical simulations. Data from field monitoring show mass-basis water contents of ~0.05 to ~0.10 that decrease towards the unsaturated ground surface and were invariant during the middle part of the dry season, except for daily fluctuations. In addition, the observed daily fluctuations in water content correlate with fluctuations in bedrock temperature, especially at depths of 2.5–5.0 cm. Periodic increases in water content occurred most notably during the day, when the bedrock temperature showed the greatest increase. Water contents then decreased to the previous state as bedrock temperature decreased during the night. Calculated vapour fluxes within the mudstone during the day increased up to 6 × 10⁻⁶–1 × 10⁻⁵ kg m⁻² s⁻¹, deriving a 0.01–0.02 increase in mass-basis water content at 2.5 cm depth for a 12-h period. This agrees with field monitoring data, suggesting that increases in water content occurred due to vapour intrusions into the bedrock. Pore water electrical conductivity (EC) showed periodic variations due to vapour intrusion, and gradually increased between the ground surface and depths of 2.5–5.0 cm. In contrast, pore water EC gradually decreased between 15 and 40 cm depth. Calculated water fluxes at depths of 2.5–40.0 cm varied from −4 × 10⁻⁶ to −2 × 10⁻⁹ kg m⁻² s⁻¹. These fluxes generated an increase in solute concentrations at the ground surface, with negative values of water flux indicating an upwards movement of water towards the surface. We show that the increase in solute content due to solute transfer from depth is highly dependent on variations in water flux with depth. © 2020 John Wiley & Sons, Ltd.     

The influence of flow discharge variations on the morphodynamics of a diffluence–confluence unit on a large river

Bifurcations are key geomorphological nodes in anabranching and braided fluvial channels, controlling local bed morphology, the routing of sediment and water, and ultimately defining the stability of their associated diffluence–confluence unit. Recently, numerical modelling of bifurcations has focused on the relationship between flow conditions and the partitioning of sediment between the bifurcate channels. Herein, we report on field observations spanning September 2013 to July 2014 of the three‐dimensional flow structure, bed morphological change and partitioning of both flow discharge and suspended sediment through a large diffluence–confluence unit on the Mekong River, Cambodia, across a range of flow stages (from 13 500 to 27 000 m³ s^?1). Analysis of discharge and sediment load throughout the diffluence–confluence unit reveals that during the highest flows (Q = 27 000 m³ s^?1), the downstream island complex is a net sink of sediment (losing 2600 ± 2000 kg s^?1 between the diffluence and confluence), whereas during the rising limb (Q = 19 500 m³ s^?1) and falling limb flows (Q = 13 500 m³ s^?1) the sediment balance is in quasi‐equilibrium. We show that the discharge asymmetry of the bifurcation varies with discharge and highlight that the influence of upstream curvature‐induced water surface slope and bed morphological change may be first‐order controls on bifurcation configuration. Comparison of our field data to existing bifurcation stability diagrams reveals that during lower (rising and falling limb) flow the bifurcation may be classified as unstable, yet transitions to a stable condition at high flows. However, over the long term (1959–2013) aerial imagery reveals the diffluence–confluence unit to be fairly stable. We propose, therefore, that the long‐term stability of the bifurcation, as well as the larger channel planform and morphology of the diffluence–confluence unit, may be controlled by the dominant sediment transport regime of the system. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Constraining tephra dispersion and deposition from three subplinian explosions in 2011 at Shinmoedake volcano,Kyushu, Japan

Constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge, because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real-time observations. Three andesitic subplinian explosions in January 2011 at Shinmoedake volcano, Japan, are used as a case study to validate selected empirical and theoretical models using observations and field data. Tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass/area. A new cubic B-spline interpolation method is also examined. Magma discharge rate is estimated using theoretical plume models incorporating the effect of wind. Results are consistent with observed plume heights (6.4–7.3 km above the vent) and eruption durations. Estimated tephra volumes were 15–34?×?10⁶ m³ for explosions on the afternoon of 26 January and morning of 27 January, and 5.0–7.6?×?10⁶ m³ for the afternoon of 27 January; magma discharge rates were in the range 1–2?×?10⁶ kg/s for all three explosions. Clast dispersal models estimated plume height at 7.1?±?1 km above the vent for each explosion. The three subplinian explosions occurred with approximately 12-h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations.     

Seasonal changes in runoff characteristics on a permafrost watershed in the southern mountainous region of eastern Siberia

We attempted to clarify the runoff characteristics of a permafrost watershed in the southern mountainous region of eastern Siberia using hydrological and meteorological data obtained by the State Hydrological Institute in Russia from 1976 to 1985. We analysed seasonal changes in the direct runoff ratio and recession gradient during the permafrost thawing period. Thawing depth began to increase from the beginning of May and continued to increase until the end of September, exceeding 150 cm. Annual precipitation and discharge were in the range 525–649 mm and 205–391 mm respectively. The sum of the annual evapotranspiration and changes in water storage ranged from 235 to 365 mm. The mean daily evapotranspiration in June, July, August and September was 1·5 mm day^?1, 1·7 mm day^?1, 1·5 mm day^?1, and 0·5 mm day^?1 respectively. The direct runoff ratio was highest in June, decreasing from 0·8 in June to 0·2 in September. The recession gradient also decreased from June to September. Since the frozen soil functioned as an impermeable layer, the soil water storage capacity in the thawing part of the soil, the depth of which changed over time, controlled the runoff characteristics. Copyright © 2005 John Wiley & Sons, Ltd.     

Rapid dome growth at Montagne Pelée during the early stages of the 1902–1905 eruption: a reconstruction from Lacroix’s data

Information obtained from various parts of the two books on Montagne Pelée by Lacroix enables an estimate to be made of the size of l’Etang Sec summit crater, the volume of the 1902–1905 lava dome and its growth rate at various stages of development. During the week preceding the 8 May nuée ardente, dome growth was between 28 and 38 m³ s^–1, leading to a volume of 17–23×10⁶ m³ on the morning of the catastrophe. Considering that significant parts of the dome (~1/3?) were removed by the 8 and 20 May climactic eruptions, a high magmatic flux could have continued until at least 27 May, when the total remaining volume was estimated to 53×10⁶ m³. After moderate activity in June–July (of order 10 m³ s^–1), vigorous dome growth resumed dramatically, leading to the third climactic eruption of 30 August (a true calculation for this period being not feasible because of poor quality of the data). From November 1902 to July 1903 most of the effusive activity was concentrated in the great spine (erupted volume ~15×10⁶ m³, magma flux 1.2 m³ s^–1), which was eventually destroyed by collapse and minor nuées ardentes. The end of the eruption was characterized by a very low effusion rate, <1 m³ s^–1 in average from August 1903 to October 1905.     

Effect of bed topography on soil aggregates transport by rill flow

After its formation, a rill may remain in the field for months, often receiving lower flow rates than the formative discharge. The objective of this work was to evaluate the rill flow transport capacity of soil aggregates at discharges unable to erode the rill, and to analyse the influence of the rill macro‐roughness on this transport process. A non‐erodible rill was built in which roughness was reproduced in detail. In order to assess only the rill macro‐roughness, a flat channel with a similar micro‐roughness to that in the rill replica was built. Rill and channel experiments were carried out at a slope of 8 and at six discharges (8·3 × 10^?5 to 5·2 × 10^?4 m³ s^?1) in the rill, and eight discharges (1·6 × 10^?5 to 5·2 × 10^?4 m³ s^?1) in the channel. Non‐erodible aggregates of three sizes (1–2, 3–5 and 5–10 mm) were released at the inlet of the rill/channel. The number of aggregates received at the outlet was registered. The number and position of the remaining aggregates along the rill/channel were also determined. The rill flow was a major sediment transport mechanism only during the formation of the rill, as during that period the power of the flow was great enough to overcome the influence of the macro‐roughness of the rill bed. At lower discharges the transport capacity in the previously formed rill was significantly less than that in the flat channel under similar slope and discharge. This was determined to be due to local slowing of flow velocities at the exit of rill pools. Copyright © 2006 John Wiley & Sons, Ltd.     

Circulation and mixing in estuary outflows

The outflow of brackish waters from the Tees estuary on an ebb tide forms a plume which is initially spread by the action of gravity. Under quiescent conditions, the rate of vertical mixing of the brackish field is relatively slow and an area of low salinity may form in the surface waters as a result of the superimposition of the outflow plumes from successive tides. A field area of some 70 km² has been observed to be enclosed by the 34.2 × 10^?3 contour.Averaged over a tidal period, the estuary outflow from the Tees forms a broad plume of low-salinity water which extends to seaward of the 20-m contour. The movement of the field thereafter depends on the residual coastal drift which runs either to the northwest or to the southeast with a typical speed of 0.015 m s^?1. The tidally averaged vertical mixing coefficient in this offshore field was estimated to be about 10^?4 m^?2 s^?1, which is similar to that off the Wear estuary and an order of magnitude smaller than that calculated for the waters off the Humber.