Drainage of Sloping Lands with Variable Recharge Model Validation and Applications

Semianalytical transient equations describing the behavior of water tables in subsurface drained soils when drains rest on a sloping impervious barrier have been derived previously and represent the bases of the SIDRA model. To validate (SIDRA), water table elevations and drainflow rates have been monitored for six years in the French Alps on fields with a slope of 8%. The predicted drain flow rates and water table shapes compare reasonably well with data of a drainage experiment site but the improvement provided by taking the slope into consideration was limited. Running the model with different slopes confirmed that high water table elevations and peak flows were not significantly changed with a slope of 8%. As could be predicted from the analysis in steady state, low water table elevations were the most affected by slope. With the soil parameters of the field experiment and from an analysis in tail recession conditions, it was shown that there is a clear threshold of 12% slope below which the slope has no significant influence and can be neglected in drainage design.     

Hydraulic Performance of a Steep Single Layer Riprap Drainage Channel

Highway drainage channels often approach slopes of 0.5 (50%). Single layer riprap-lined channels at this slope have been constructed for highway drainage and appear to perform satisfactorily, but no quantitative information is available to guide their hydraulic design. A 1/6 scale laboratory hydraulic model, using a single layer of sized crushed limestone, was constructed to determine the relationship between depth of flow and discharge. The flow range investigated took place at depths near or below the top of the riprap, since riprap instability occurred at greater depths. Standing waves and localized hydraulic jumps dominated the surface of the flow, which held streamwise-averaged Froude numbers in a narrow range near the critical condition for those flow depths for which the channel is designed. This resulted in a simple relationship between unit discharge and depth of flow that applies to the model and prototype channels.     

Back-Analysis Approach for the Design of Drainage Systems

The geotechnical design of drainage or dewatering systems requires a free surface seepage analysis to evaluate the water flux that corresponds to the sought lowering of the water table. It is observed in practice that sometimes the calculated flux is not sufficient to reach the predicted result, even when the hydraulic conductivity of the soil mass has been properly determined. This prevents the initiation of the in situ works (e.g., excavation) with a relevant economical loss. The possible causes of this problem are investigated through a series of two- and three-dimensional unconfined seepage analyses. They show that the numerical results strongly depend on the characteristics of the numerical model and that, consequently, the computed fluxes and lowering of the water table do not necessarily correspond to the field conditions. To overcome this drawback a back-analysis approach is suggested for calibrating the numerical model adopted in design. An application of this technique to an actual field problem is finally discussed.     

Estimation of Maximum Liquid Depth in Layered Drainage Blankets over Landfill Barriers

Based on an extended form of the Dupuit assumption, this technical note proposes a computational solution for calculating the maximum liquid depth (Dmax) in layered porous media (e.g., geosynthetic and/or soil drainage blankets of landfills) under free discharge condition. The liquid profile and the location of Dmax for either homogeneous media or layered media can be provided from the approach presented in this technical note. In comparison with the results obtained by application of other methods, the presented approach is verified. Most approaches other than the presented method may lead to considerable error, especially when applied to the drainage system, which consists of a drainage geocomposite overlain by a sand layer with low hydraulic conductivity. The variations of Dmax in two-layered drainage media with varying geometrical parameters and varying hydraulic properties are studied by a parametric analysis. The results demonstrate for a medium consisting of two sand layers, if the hydraulic conductivity of the upper layer is smaller than that of the lower layer and the maximum liquid thickness above the barrier exceeds the thickness of the lower layer, Dmax is very sensitive to the hydraulic conductivity of the upper layer. For a medium consisting of a drainage geocomposite overlain by a sand layer, Dmax is significantly influenced by inflow rate, transmissivity of the geocomposite, and the hydraulic conductivity of the sand when they are not extraordinarily low, and Dmax is much more sensitive to the slope of the drainage layer compared with the system consisting of two sand layers. It is of great advantage to increase the inclination when geocomposites are applied as drainage material.     

Well-Balanced Bottom Discontinuities Treatment for High-Order Shallow Water Equations WENO Scheme

A finite volume well-balanced weighted essentially nonoscillatory (WENO) scheme, fourth-order accurate in space and time, for the numerical integration of shallow water equations with the bottom slope source term, is presented. The main novelty introduced in this work is a new method for managing bed discontinuities. This method is based on a suitable reconstruction of the conservative variables at the cell interfaces, coupled with a correction of the numerical flux based on the local conservation of total energy. Further changes regard the treatment of the source term, based on a high-order extension of the divergence form for bed slope source term method, and the application of an analytical inversion of the specific energy-depth relationship. Two ad hoc test cases, consisting of a steady flow over a step and a surge crossing a step, show the effectiveness of the method of treating bottom discontinuities. Several standard one-dimensional test cases are also used to verify the high-order accuracy, the C-property, and the good resolution properties of the resulting scheme, in the cases of both continuous and discontinuous bottoms. Finally, a comparison between the fourth-order scheme proposed here and a well-established second-order scheme emphasizes the improvement achieved using the higher-order approach.     

Site Investigations for Involvement of Water Films in Lateral Flow in Liquefied Ground

Previous research indicates that if layered sand deposits are liquefied during earthquakes, water films are likely to develop beneath less permeable sublayers and lead to the destabilization of sloping ground. In Niigata City, large lateral flow displacements were reported in almost flat areas during the 1964 Niigata earthquake. The involvement of water films in lateral flow failure during the earthquake is examined in this research based on site investigation data. Soil profiles in the investigated areas estimated from many borehole logs indicate that continuous or partially continuous sublayers of fine soil that cap liquefiable loose sand exist. Elevation contours of 0.1 m increments are drawn based on an in situ leveling survey and local maps. The ground slopes obtained are found to be closely related to flow displacements evaluated in previous research, indicating that a gentle slope of less than 1% results in displacement of several meters. This strongly suggests that water films with literally no shear resistance formed beneath fine soil sublayers were highly responsible for the large lateral flow displacements in these areas during the Niigata earthquake.     

浅谈选矿厂给排水设计

简单介绍了(有色金属)矿山工程选矿厂给排水设计的重要性,同时对矿山工程选矿厂给排水设计中的水量平衡、生产废水处理、高位水池的设置及回水泵站吸水池的设计提出看法。     

Water Table Fluctuation in the Presence of a Time-Varying Exponential Recharge and Depth-Dependent ET in a Two-Dimensional Aquifer System with an Inclined Base

An analytical solution is presented for water table fluctuation between ditch drains in presence of exponential recharge and depth-dependent evapotranspiration (ET) from groundwater table in a two-dimensional gently sloping aquifer. The groundwater head above the drain is small compared to the saturated thickness of the aquifer. A sound mathematical transformation is devised to transform the two-dimensional groundwater flow equation into a simple form, which makes possible to obtain an analytical solution. The transient midpoint water table variations from the proposed solution compare well with the already existing solutions for horizontal aquifer. A numerical example is used to illustrate the combined effect of depth-dependent ET coupled with a time-varying exponential recharge on the water table fluctuation. The inclusion of a depth-dependent ET in the solution results in water table decline at a faster rate as compared to the case when ET is not considered. With an increase in slope of the aquifer base, water table profiles become asymmetric and the water table divide shifts towards the lower drain. The height of the water table profiles increases on moving away from the boundary of the aquifer and the highest level of the ground water table is obtained in the central portion of the aquifer basin due to the presence of drainage ditches on the aquifer boundary. When the effect of ET is incorporated in combination with recharge, the analytical solution results in accurate and reliable estimates of water table fluctuations under situations subjected to a number of controlling factors. This study will be useful for alleviation of drainage problems of the aquifers receiving surface recharge and surrounded by streams.     

南昌市地铁车站给排水设计

以南昌市地铁车站给排水设计为例,简要论述了地铁工程作为典型的地下市政工程在设计上鲜明的自身特点和特殊的技术要求。     

Approach to Control the Depth of Water in Basin Irrigation and Wetland Flooding

The controlled ponding of water over level terrain in basin irrigation or wetland flooding is described quantitatively as a three-phase process. During the first phase, water is applied at a known rate until ponding emerges at the time of ponding initiation. In the second phase, water continues to be applied at the same rate until a desired ponded depth is attained. In the third phase, water is applied to maintain the desired ponded depth during an arbitrarily long period. The desired ponded depth is maintained by adjusting the water-application rate to equal the infiltration rate plus the evaporation rate. The time of ponding, the ordinary differential equations (ODEs) governing cumulative infiltration during the second and third phases, and the water-application rate during the third phase are derived in this work using an extended Green-and-Ampt formulation of infiltration. Computational examples illustrate the solutions of the derived ODEs and their application in the control of basin irrigation and wetland flooding.     

Short-Duration Rainfall Intensity Equations for Urban Drainage Design

A practical method for developing rainfall-intensity equations for short durations (approximately one hour or less) for locations in the United States covered by NOAA Atlas 14 Volumes 1, 2, 3, and 4 is presented. For the semiarid western United States covered by Volume 1, for Puerto Rico and the U.S. Virgin Islands covered by Volume 3, and for Hawaii covered by Volume 4, single formulas apply to rainfall of all average recurrence intervals (ARIs). For the central and mid-Atlantic regions of the United States covered by Volume 2, formula coefficients are provided for several ARIs ranging from 1.58 to 1,000 years. All equations are based on a single-term exponential expression plus a constant that provides excellent fits to the available data. Mathematical expressions for the central and mid-Atlantic region coefficients as functions of the ARI are provided to simplify application of the approach. Mathematical relations representing design storm hyetographs are developed using the intensity-duration expression by distributing rainfall about the time of peak intensity proportioned by a factor r = tp/td, where tp = time to peak rainfall intensity, and td = storm duration.     

Divergence Form for Bed Slope Source Term in Shallow Water Equations

A novel technique is presented for the treatment of the bed slope source terms within the numerical solution of the shallow water equations. The proposed method consists of writing the bed slope source term as the divergence of a proper matrix, related to the static force due to bottom slope. Such a technique is founded on analytical reasoning and is physically based, so that it can be easily applied to a wide range of numerical models, as it is completely independent of any adopted discretization technique, and requires a minimum computational effort. Herein, we show an application to a Godunov-type model, second order accurate both in space and time, based on the finite-volume method. The presented technique leads to a strong improvement in the source terms numerical treatment, especially for steady states, in which flux gradients are exactly balanced by source terms. A surprising degree of simplicity is maintained, with respect to different existing methods. The numerical model has been applied to a set of classical test cases and to a selected laboratory experiment, in order to verify its stability, accuracy, and applicability to practical real-world cases.     

大型仓储式超市给排水设计中应注意的问题

通过对南昌万达沃尔玛购物广场、东方家园建材超市南昌店等大型仓储式超市的给排水设计，总结在此类设计中值得注意的问题。     

人民防空地下室给排水设计探讨

主要介绍设在民用建筑地下室内的五级、六级设防的人员掩蔽防空地下室给水、排水、消防设计的常见作法、设计要点、有关要求。     

南北方工业给排水设计差异

从给水和排水管网、消防给水系统和工业循环冷却水系统4个方面介绍了南方地区及北方地区工业给排水设计的不同及其注意事项。     

乐平市排水专项规划设计

介绍了乐平市的城市概况及排水现状,针对其排水现状及地形地势特征,排水专项规划从实际出发,科学合理地提出了用水量指标的取值,专项规划的污水量预测合理,规划方案可行,对乐平市的排水系统建设具有较强的指导意义。     

浅谈铜冶炼企业给排水设计

为了贯彻国家节约水资源和保护环境的方针政策,铜冶炼企业给排水设计应在满足企业安全、高效生产与相关规范的前提下,根据水源情况及用水户对水量、水质、水温等要求,合理用水,一水多用,废水回用与循环使用,使水的重复利用率满足相关要求,尽可能降低吨铜新水耗量和排污量。     

Water Quality Aspects of Irrigation and Drainage: Past History and Future Challenges for Civil Engineers

This paper presents a brief history of irrigation and drainage related to ASCE activities on its Jubilee. This paper discusses legislation and policies that affect irrigation and drainage practices, water quality constituents of increasing concern in irrigation and drainage practices, and presents a prognosis on the future of declining freshwater resources available for irrigated agriculture and growing water quality problems in irrigation and drainage. Civil engineers in ASCE’s Irrigation and Drainage Division have compiled an 80-year history of highly meritorious service and accomplishments. In the next millennium, civil engineers will face a formidable challenge in managing and protecting the precious freshwater resources in the U.S.     

Optimal Design of a Settling Basin for a Small-Scale Drainage Area

This paper develops a nonlinear programming model to optimally design a settling basin for a small-scale drainage area with a minimum total cost. It is assumed that the shape of the settling basin is rectangular parallelepiped, and it is connected to an open channel at both ends. Therefore, the decision variables include the scales of the settling basin (i.e., length, width, and height) and the scales of the channel (i.e., width and height). The design trap efficiency requirement, which must be greater than or equal to the required one of the considered watershed, makes up the main constraint. Other constraints consist of the upper and lower bounds of the decision variables, the equations for computing the trap efficiency, and the average flow velocity in the settling basin. The objective function is to minimize the total annual cost, which is the sum of the land, capital, and maintenance-operation cost. The developed model is solved by using a genetic algorithm. This model is applied to a subwatershed of the Wu-She Reservoir watershed in central Taiwan. The obtained results effectively demonstrate the applicability and practicability of the model.