Dynamics of suspended sediment transport at field‐scale drain channels of irrigation‐dominated watersheds in the Sonoran Desert,southeastern California     

Peng Gao  Gregory Pasternack 《水文研究》2007,21(16):2081-2092

Suspended sediment is a major source of pollution in irrigation‐dominated watersheds. However, little is known about the process and mechanisms of suspended sediment transport in drain channels directly connected to agricultural fields. This paper explains sediment dynamics using averaged 5 min flow discharge Q (m³ s^?1) and suspended sediment concentration C (mg l^?1) collected during one crop season in a small catchment containing a first‐order drain channel and its connected six agricultural fields within the Salton Sea watershed. The statistical properties and average trends of Q and C were investigated for both early (i.e. November) and late (i.e. January) stages of a crop season. Further in‐depth analysis on sediment dynamics was performed by selecting two typical single‐field irrigation events and two multiple‐field irrigation events. For each set of irrigation events, the process of suspended sediment transport was revealed by examining hydrograph and sediment graph responses. The mechanisms underlying suspended sediment transport were investigated by analysing the types of corresponding hysteresis loop. Finally, sediment rating curves for both hourly and daily data at early and late stages and for the entire crop season were established to seek possible sediment‐transport predictive model(s). The study suggests that the complicated processes of suspended sediment transport in irrigation‐dominated watersheds require stochastic rather than deterministic forecasting. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Use of turbidometry to characterize suspended sediment and phosphorus fluxes in the Lake Tahoe basin,California, USA     

Andrew P. Stubblefield  John E. Reuter  Randy A. Dahlgren  Charles R. Goldman 《水文研究》2007,21(3):281-291

The efficacy of in‐stream nephelometric turbidometry as a surrogate for total suspended solids (TSS) and total phosphorus (TP) concentrations was evaluated for use in low turbidity (<50 NTU) subalpine watersheds at Lake Tahoe, California–Nevada, USA. Continuous turbidity records for the 1999, 2000 and 2001 snowmelt seasons and data from water quality samples (1982–2000) were examined to determine watershed sediment delivery dynamics. Strong correlations were found between turbidity and both TSS and TP concentration. The strong correlation indicates that turbidity can serve as a good surrogate for direct measurement in these watersheds. The watersheds displayed clockwise hysteresis: sediment flushing and depletion, on daily, seasonal and decadal time‐scales. The hysteresis curves had strong concave shapes, indicating a sensitive response to peak flow. A pronounced seasonal trend was observed for the ratio of suspended sediment concentration (SSC)/discharge over time, indicating early season flushing of available sediment. Significant linear relationships (p < 0·05) were found for 12 of 17 years. Comparison of annual sediment rating curve coefficients indicated smaller coefficients during high sediment loading years and in the years following. The smaller coefficients are evidence of sediment depletion during high flow years. The effect of hysteresis on monitoring methods was illustrated by comparing turbidity estimates of TSS load with sediment rating curve estimates of SSC. After accounting for differences in SSC/TSS methods of analysis, daily loads calculated with turbidity methods were 58–98% of rating curve estimates for the spring snowmelt seasons of 1999–2001. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Suspended sediment dynamics at high and low storm flows in two small watersheds     

Nira L. Salant  Marwan A. Hassan  Carlos V. Alonso 《水文研究》2008,22(11):1573-1587

A record spanning almost 20 years of suspended sediment and discharge measurements on two reaches of an agricultural watershed is used to assess the influence of in‐channel sediment supplies and bed composition on suspended sediment concentrations (SSC). We analyse discharge‐SSC relationships from two small streams of similar hydrology, climate and land use but widely different bed compositions (one dominated by sand, the other by gravel). Given that sand‐dominated systems have more fine sediment available for transport, we use bed composition and the relative proportion of surface sand and gravel to be representative of in‐channel sediment supply. Both high flow events and lower flows associated with onset and late recessional storm flow (‘low flows’) are analysed in order to distinguish external from in‐channel sources of sediment and to assess the relationship between low flows and sediment supply. We find that SSC during low flows is affected by changes to sediment supply, not just discharge capacity, indicated by the variation in the discharge‐SSC relationship both within and between low flows. Results also demonstrate that suspended sediment and discharge dynamics differ between reaches; high bed sand fractions provide a steady supply of sediment that is quickly replenished, resulting in more frequent sediment‐mobilizing low flow and relatively constant SSC between floods. In contrast, SSC of a gravel‐dominated reach vary widely between events, with high SSC generally associated with only one or two high‐flow events. Results lend support to the idea that fine sediment is both more available and more easily transported from sand‐dominated streambeds, especially during low flows, providing evidence that bed composition and in‐channel sediment supplies may play important roles in the mobilization and transport of fine sediment. In addition, the analysis of low‐flow conditions, an approach unique to this study, provides insight into alternative and potentially significant factors that control fine sediment dynamics. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Micromechanics of saturated and unsaturated porous media     

Xavier Chateau  Luc Dormieux 《国际地质力学数值与分析法杂志》2002,26(8):831-844

The homogenization method is used to determine the formulation of the behaviour of both saturated and unsaturated porous media. This approach makes it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale. Furthermore, the influence of the morphologies of the solid and fluid phases on the macroscopic behaviour is studied. The strain induced by drying is examined as a function of the morphological properties. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Diurnal variations in discharge and suspended sediment concentration,including runoff‐delaying characteristics,of the Gangotri Glacier in the Garhwal Himalayas     

Pratap Singh  Umesh K. Haritashya  K. S. Ramasastri  Naresh Kumar 《水文研究》2005,19(7):1445-1457

Diurnal variations in discharge and suspended sediment concentration (SSC), including runoff delaying characteristics, have been studied for the Gangotri Glacier, the largest glacier in the Garhwal Himalayas (glacierized area 286 km²; drainage area 556 km²). Hourly discharge and SSC data were collected near the snout of the glacier (∼4000 m) at an interval of about 15 days for an entire ablation period (May–October 2001). Diurnal variability in SSC was found to be much higher than the discharge. Hysteresis trends between discharge and SSC were established. Results indicate that, for the study glacier, clockwise hysteresis dominated for the entire melt season, indicating that most of the time the SSC led the discharge. During the peak melt period, anticlockwise hysteresis was also observed for a few hours. Assessment of runoff‐delaying characteristics was made by estimating the time lag between the occurrence of melting and its appearance as runoff along with estimation of time to peak. A comparison of runoff‐delaying parameters with discharge ratio clearly indicated that changes in time lag and time to peak are inversely correlated with variations in discharge. Attempts have also been made to establish the relationship between discharge and SSC using short‐interval data. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Influence of soil moisture hysteresis on the functioning of capillary barriers     

Qi Zhang  Adrian D. Werner  Raden F. Aviyanto  John L. Hutson 《水文研究》2009,23(9):1369-1375

Previous experimental studies of capillary barriers have identified highly hysteretic soil moisture retention characteristics in the materials used. In this study, numerical modelling is used to analyse the role of soil moisture hysteresis in capillary barrier functioning. Comparisons between published experimental results and model simulations indicate that soil moisture hysteresis was a necessary inclusion in the modelling approach to adequately reproduce pore water pressure distributions and the timing of breakthrough occurrences. Under hypothetical intermittent infiltration and evaporation conditions, the predicted volumetric water content in the moisture retention layer was significantly different for hysteretic and non‐hysteretic models. The hysteresis effect was found to be dependent on the nature of infiltration–evaporation cycling, although the predicted volume of flow through the hysteretic barrier was lower than that of the non‐hysteretic case, regardless of the nature of the cyclic upper boundary conditions. For practical engineering designs, where the water leakage through the barrier is the primary concern, the inclusion of soil moisture hysteresis in numerical modelling is needed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

极低屈服点软钢阻尼器恢复力模型的研究   总被引：3，自引：0，他引：3  

李玉顺  大井谦一  沈世钊 《地震工程与工程振动》2004,24(6):142-145,153

本文通过试验和理论分析探讨极低屈服点软钢阻尼器的恢复力特性。随着塑性变形的发展将恢复力模型中的骨架曲线进行平移,其卸载曲线用Ramberg—Osgood函数来描述,由此得到的恢复力模型定义为骨架平移模型,将其应用于描述极低屈服点软钢阻尼器的恢复力特性、为了验证该馍型的有效性并确定合理的参数,对安装极低屈服点软钢阻尼器的3层钢框架结构进行了拟动力试验．同时用该骨架平移模型模拟极低屈服点软钢阻尼器的恢复力特性进行了大量的弹塑性地震反应分析,通过取用不同平移系数时的数值计算结果与拟动力试验结果的比较,发现平移系数为0．6左右时,该模型具有较高的精度。  相似文献   

华北平原典型地段地面沉降演化特征与机理研究   总被引：3，自引：2，他引：1       下载免费PDF全文

郭海朋  白晋斌  张有全  王丽亚  石菊松  李文鹏  张作辰  王云龙  朱菊艳  王海刚 《中国地质》2017,44(6):1115-1127

华北平原是世界上最大的地下水系统之一,地面沉降问题突出。由于沉积环境变化多样、地质条件差异性显著和人类开采活动强烈,使得该地区地面沉降成因机理复杂。本文采用卫星对地观测技术与传统手段相结合,监测地面沉降灾变过程,分析华北平原地面沉降发展历史和现状。结合应力-应变图解法及土工实验研究地面沉降差异性特征及滞后变形成因机理。取得了以下关键认识:(1)华北平原地面沉降空间分布差异性明显,沉降主要分布在平原区第四纪沉积凹陷,呈现东西分带、南北分段特点。地面沉降空间发展部分受到北东向和北西向构造控制。在沧县隆起区,地面沉降也比较发育,主要原因是沧县隆起在第四纪时期构造运动相对不活跃,沉积了较厚的第四系;存在与构造走向一致的3期古河道,该地区赋存丰富的地下水资源并被大量开采。(2)地面沉降发生发展与地下水开采历史密切相关,沉降主要压缩贡献层随地下水开采层位变化而变化。北京平原100 m以深地层对地面沉降贡献呈增加趋势。天津平原目前地面沉降的主要贡献层来自300 m以下地层。(3)气候干旱导致地下水补给量减少,同时增加了地下水的开采,因而是引起地面沉降的重要间接驱动因素。高层建筑荷载、基坑降排水、地热开采对地面沉降的影响应引起足够重视。(4)地面沉降具有很强的滞后性,最大滞后时间可达25年。除了渗透固结成因以外,土体蠕变是另外一个重要原因。更新世地层在不同荷载下,蠕变特征明显。沧县隆起晚更新世地层次固结可达到总变形28.3%。(5)土的物理性质、地下水位变化模式对土层变形特征具有重要影响。不同埋深地层在地下水位变化条件下的变形特征存在较大的差异(弹性、黏弹性、黏弹塑性)。浅部含水组呈现以弹性为主的变形特征。  相似文献   

基于压磁效应的锈蚀钢筋应力状态检测试验研究     

金伟良  项凯潇  毛江鸿  徐方圆  张军 《海洋工程》2017,35(6):62-70

钢筋锈蚀是严重威胁结构安全的耐久性问题,基于压磁效应,研究均匀锈蚀和坑蚀两种锈蚀钢筋的应力状态与压磁场变化的关系。首先,采用通电加速锈蚀方法进行钢筋均匀锈蚀和点蚀试验;然后,通过轴向拉伸静载试验和疲劳加载试验,分析锈蚀钢筋的压磁信号特征。试验结果显示,磁感强度与钢筋应力状态之间具有较好的对应关系,屈服阶段不同锈蚀率下的钢筋磁感强度曲线有较明显区别,疲劳荷载作用下锈蚀钢筋的法向残余磁感强度和磁滞回环面积均呈现疲劳三阶段变化规律,可进一步运用于钢筋应力状态的检测中。  相似文献   

水位变化条件下粘性土渗流特征试验研究     

曹文炳  万力  龚斌  王大纯 《水文地质工程地质》2006,33(2):118-122

开采孔隙承压含水系统，引起含水层水头下降。通常认为相邻含水层一经出现水头差，便会有通过粘性土层的越流渗透。但在粘性土两侧含水层出现水头差初期，粘性土内部水头降低缓慢，并伴随有释水压密过程。本文采用多用途饱水粘性土固结和渗透试验装置，对不同岩性的粘性土原状样进行了释水、吸水与越流发展过程之间关系的试验。试验表明，含水层水位升、降变化，首先引起相邻粘性土吸水回弹或释水压密，而后出现粘性土吸水或与释水越流并存阶段。越流的出现。明显滞后于含水层水头变化，当吸水或释水过程结束后，越流渗透达到稳定。越流滞后时间与土的固结程度有关，笔者采用一维固结理论提出了计算越流滞后时间的方法。  相似文献