Entrance Head Research Articles

Knitted-sock geotextile envelopes increase drain inflow in subsurface drainage systems

A knitted-sock geotextile envelope is commonly used in the USA, Canada, and parts of Europe to prevent sediment entry into agricultural subsurface drain pipes. Sand-slot pipes have a narrow width to prevent sediment from moving into the drain pipe, and they are used in the USA and Canada as a cheaper alternative to knitted-sock-wrapped pipes. The type of drain pipe (sand-slot or sock-wrapped) is important in subsurface drainage design because it affects the entrance head loss caused by the convergence of flowlines toward the drain perforations, thereby influencing the effective radius of the pipe, which in turn affects drain inflow. Although the theoretical effective radius of a knitted-sock-wrapped pipe can be estimated based on analytical equations, no study has experimentally measured it to verify the theoretical equations. This study had two objectives: (1) Experimentally measure the effective radius of sock-wrapped and sand-slot pipes to verify the theoretical method, and (2) comparatively evaluate the drain inflow performance of a sock-wrapped pipe and a sand-slot pipe. We tested the pipe materials in a sand-tank experiment equipped with manometers. The results showed that the measured and theoretical effective radii were 5.5 and 5.6 cm for the sock-wrapped pipe, 0.7 and 0.7 cm for the 4-row sand-slot pipe, and 1.6 and 1.6 cm for the 8-row sand-slot pipe, respectively. This agreement confirmed that the theoretical method reliably estimated the effective radius of the pipes. The sock-wrapped pipe had a considerably lower entrance head loss (0.4 cm) than the 8-row (6.1 cm) and 4-row (10.4 cm) sand-slot pipes, thereby increasing the effective radius of the sock-wrapped pipe. The estimated drain inflow of the sock-wrapped pipe was 12% and 20% higher than that of the 8-row and 4-row sand-slot pipes, respectively. In conclusion, we verified that the theoretical method accurately estimated the effective radius of the pipes and demonstrated that the sock-wrapped pipe had considerably higher drain inflow than the sand-slot pipe.

Investigation on Flow Maldistribution and Thermo-Hydraulic Performance of PCHEs with Spoiler Perforated Boards

In this study, the effects of the maldistribution coefficient on the thermo-hydraulic performance of discontinuous fin printed circuit heat exchanger (DF-PCHE) entrance head and channels are numerically investigated. To improve the flow uniformity at the entrance head, the flow in the exchanger with three types of spoiler perforated boards (SPBs) having 3 × 3, 4 × 4, and 5 × 5 holes and three kinds of hole diameters (Φd = 30, 25, and 20 mm), respectively, are compared to the flow in an exchanger with no SPB. The results show that a small maldistribution coefficient for the inlet velocity field is beneficial for the thermo-hydraulic performance of the DF-PCHE channels, and a maldistribution coefficient of 0.7 is an acceptable velocity distribution for the PCHE channel inlet. Using the 3 × 3 SPB with Φd = 30 mm, the maldistribution coefficient becomes 0.7, the fastest among all the SPB application cases at ΔL = 150 mm. Moreover, its heat transfer coefficient and pressure drop increase by 22.46% and decreases by 47.2% compared to those of the exchanger without SPB, respectively.

Choice of Pipe Material Influences Drain Spacing and System Cost in Subsurface Drainage Design

HighlightsFor 3- or 4-row regular-perforated pipes, the effective radius ranged from 0.3 to 0.9 cm (average 0.6 cm).For 8-row regular-perforated pipes, the effective radius was 1.9 cm.The effective radius of sock-wrapped pipes ranged from 5.7 to 6.0 cm (average 5.9 cm).The 8-row sand-slot pipes had a lower initial system cost than the sock-wrapped pipes.The 8-row regular-perforated pipes had a lower initial system cost than the 4-row regular-perforated pipes.Abstract. Knitted-sock envelopes are applied in agricultural subsurface drainage to prevent sediment clogging of the drain pipes. In the United States and Canada, sand-slot pipes are sometimes used as a cheaper alternative to sock-wrapped pipes. However, their initial system cost has not been compared. The main objective of this study was to evaluate the effect of pipe material on drain spacing and initial system cost. First, the theoretical effective radius of each pipe material was estimated. Then, the drain spacing was calculated for each pipe material in a drainage design, such that each pipe would provide the same design drainage rate (i.e., same water removal rate). The results showed that the effective radius of sock-wrapped pipes (average 5.9 cm) was much greater than that of 4-row (average 0.4 cm) and 8-row perforated sand-slot pipes (average 1.6 cm). Rows refer to number of longitudinal rows of perforations. The sock-wrapped pipes considerably increased the effective radius of the pipe by reducing the entrance head loss. Furthermore, the sock-wrapped pipes allowed for a wider drain spacing (ranging from 0.8 to 5.4 m wider) in soil with risk of drain sedimentation, thereby reducing the total length of the lateral drain pipe needed for drainage design compared to both 4- and 8-row sand-slot pipes. The 8-row regular-perforated pipes allowed for a wider optimum drain spacing, thereby reducing the initial system cost in soil without a drain sedimentation issue compared to 4-row regular-perforated pipes. In conclusion, even though the sock-wrapped pipe reduced the total length of the lateral drain pipe, the 8-row sand-slot pipe had a lower initial system cost compared to the sock-wrapped pipe, when designed at the same design drainage rate and drain depth. Keywords: Drain spacing, Effective radius, Entrance resistance, Geotextile, Knitted sock, Perforation.

Development of Fishway Assessment Model based on the Fishway Structure, Hydrology and Biological Characteristics in Lotic Ecosystem

The main goal of this study is to develop a multi-metric fishway assessment model (M m-FA) and evaluate the efficiency of fishway. The M m-FA model has three major fishway components with nine metrics: structural characteristics, hydraulic/ hydrologic features, and biological attributes. The model was developed for diagnosing and assessing fishway efficiency and tested to Juksan Weir at the Yeongsan River Watershed. Structural characteristics of fishway included slope of the fishway (M 1), ratios of fishway width to stream width (M 2), and the proportion of orifice clogging and orifice size (M 3). Hydraulic/hydrologic characteristics included depth of fishway entrance head (M 4), depth of exit tail (M5), and current velocity of inner fishway (M 6). Biological characteristics included fish species ratio of inner fishway to upper-lower weir (M7), fish length distribution (M 8), and the proportion of migratory fish species to the total number of species (M 9). Overall, the assessment of fishway efficiency showed the total score of the M m-FA model was 25 in the Juksan Weir, indicating “good condition” by the criteria of the five-level classification system. The M m-FA model may be used as a key tool for the assessment of fishway efficiency, especially on the 16 weirs constructed for the “Four Rivers Restoration Project” after a partial calibration of Mm-FA model.

Simulating unsaturated flow and transport in a macroporous soil to tile drains subject to an entrance head: model development and preliminary evaluation

Accurate prediction of water flow and chemical transport in agricultural soil profiles requires the use of a simulation model that considers the most important physical, hydrological and chemical processes. Two important flow-related processes in tile-drained field systems are macropore flow and water discharge from the tile drains. To better account for these two processes, we extended an existing two-dimensional model (SWMS_2D) by adding a macropore flow component as well as a Hooghoudt type boundary condition that considers the presence of an entrance head at the tile drain. The macropore component is necessary to account for water and solutes short-circuiting the soil matrix, while the drainage entrance head is needed to account for the contraction of streamlines around the drains, a feature that causes delayed discharge. The applicability of the new model to a landfill problem was examined. The simulation results, which included water flow and solute transport, compared well with other models.

Application of a two‐dimensional model to simulate flow and transport in a macroporous agricultural soil with tile drains

SummaryIt is essential that important field processes are taken into account to model water flow and chemical transport accurately in agricultural fields. Recent field studies indicate that transport through macropores can play a major role in the export of solutes and particulates from drained agricultural land into surface water. Non‐ideal drain behaviour may further modify the flow and transport. We extended an existing two‐dimensional flow and transport model for variably saturated soils (SWMS_2D) by adding a macropore domain and an additional Hooghoudt drain boundary condition. The Hooghoudt boundary condition accounts for an entrance head needed to initiate flow into the drains. This paper presents the application of the new model (M‐2D) to an agricultural field in Switzerland. To understand interactions between macropore flow and drains better we simulated water flow and bromide transport for four different field scenarios. We considered both collector drains only with an ideal drain boundary condition (with and without macropores) and collectors and laterals with a Hooghoudt boundary condition (also with and without macropores). For each scenario, inverse modelling was used to identify model parameters using 150 days of data on observed cumulative discharge, water table depth, and tracer concentration. The models were subsequently tested against a 390‐day validation data set. We found that the two additional components (macropore flow, drain entrance head) of the M‐2D model were essential to describe adequately the flow regime and the tracer transport data in the field.

Transient analysis for compressible fluid flow in transmission line by the method of characteristics

Transient analysis for compressible fluid flow has been conducted to evaluate the dynamic characteristics of the dead-ended or volume-terminated transmission lines following a sudden pressure change at its entrance. The two partial-differential equations, based on the conservation of mass, energy and momentum, were derived for the one-dimensional adiabatic compressible flow with friction and entrance head loss. The governing equations describing the present transient-state flow are hyperbolic, and the boundary conditions include a fixed volume termination at the exit and sinusoidal disturbance in the sudden pressure change at tube entrance. The method of characteristics is used to transform the partial differential equation into the particular total differential equations, which can be integrated along the characteristic lines. The present result shows good agreements with the existing results. The effects of tube length. tube diameter and end volume are evaluated on the responses of the pressure and on the damping factor.

Filling of Pipelines with Undulating Elevation Profiles

A model is formulated to describe the unsteady motion of a lengthening rigid water column filling an empty pipeline with an undulating elevation profile. The model gives time histories of the water column's length, velocity, and pressure at various locations. A criterion to judge the applicability of the model is given in terms of air intrusion at the advancing front. The early phase of filling was investigated experimentally. The model yields velocities comparable with the experimental data. A high but short-lived peak velocity can occur when the inlet submergence is large, the entrance head loss small, and the length of water column short. As the column lengthens, it accelerates or decelerates according to the undulating profile, the inertia of the column, and the velocity history. The interaction of these variables is captured by the model. Applications of the model for assessing the velocity history and for judging the occurrence of column separation in filling an undulating pipeline are demonstrated by an example.

Hydraulic calculation of side filtering intake structures

1. The main factors affecting the capacity of the dam are: porosity of the dam, diameter of the particles composing the dam, entrance head into the dam, and dam width. The effect of the average water velocity in the flume on the seepage discharge is insignificant. 2. The main factors affecting the intake ratio are: water velocity in the flume, dam width, particle diameter, and dam porosity. 3. The width of the zone of influence on the dam width, water velocity in the flume, and particle diameter. The water depth in the flume does not substantially affect the width of the zone of influence. 4. Seepage in the dam body become turbulent with increase of particle diameter. At the same time, the dependence of the Re number of the dam on the Re number of the flume is stronger for large particle diameters than for small.

Measurement of Irrigation Flows through Irrigation Turnouts

Accurate measurement of applied water volumes in surface irrigation fields is important towards improving irrigation efficiencies and management of the surface irrigation system. In flood irrigated fields, applied water may be supplied through spiles, or turnout pipes connecting the field directly to the supply canal. A simple measurement of head loss across the turnout pipe is all that is necessary to estimate onflow rates when the total head loss coefficient for the spile is known. The total head loss coefficient is primarily dependent on the entrance and exit head losses, and entrance head losses depend on the orientation of flow in the canal relative to the spile. For spile flows perpendicular to the axis of canal flow, the entrance head loss is greater than traditionally assumed. This paper reports results of field calibration of spiles having a supporting bracket for the cover plate, perpendicular flow and into which flow develops a sizable vortex that dissipates energy. A calibration curve relating head loss to spile discharge is developed from the field data.

Head Losses in Storm Sewer Manholes: Submerged Jet Theory

The design of storm sewers especially suffers from lack of knowledge of the head losses in manholes. A submerged jet theory for the flow in manholes with straight throughflow has been outlined. The entrance head loss has been related to the kinetic energy transformation associated with the entrainment/detrainment in the jet. The exit head loss is calculated as a Carnot-loss in connection with the vena contracta in the exit pipe. The jet theory and the experiments have shown that the only governing parameter for a specific manhole shape is the ratio of manhole diameter to pipe diameter. The theory has been compared to laboratory experiments. The head loss in storm sewer manholes is shown to be considerably smaller than the values calculated by traditional formulas.

Laboratory Testing of Filters and Slot Sizes for Relief Wells

Results of a laboratory experimental program conducted to evaluate three different criteria for the selection of the required screen slot width for gravel pack relief wells are presented. A widely graded filter is used in conjunction with continuous slot screen sections based on the D20 size and the D50 size of the filter. A third test involves a uniform filter with a continuous slot screen section based on the D10 size of the filter. The two filters are compared in terms of (1) Entrance head losses; (2) amount of material entering the screen; and (3) effective radius of the well. The investigation indicates that all three systems result in minimal entrance head losses at the screen. The largest loss of filter material occurs in the well designed with the D50 size of the filter. A larger effective well radius is obtained using the widely graded filter. The conclusion applies to conditions shortly after the well is installed and does not consider changes in entrance losses after clogging of well screens an...

Estimation of Uplift in Cracks in Older Concrete Gravity Dams: Analytical Solution and Parametric Study

An analytical solution is proposed to model the internal uplift pressures associated with cracks in older concrete gravity dams and assess drain effectiveness. Each crack is assumed to be finite, rectangular with constant aperture and surface properties and in direct hydraulic connection with the water in the reservoir. Flow in the crack is laminar, steady and is a potential flow. The crack is intersected by a single drainage well or a line of drainage wells. A parametric study is presented to study the effect of the following parameters on uplift; (1) Crack elevation, entrance head, geometry, aperture, and roughness; (2) drain radius and location; and (3) drain boundary conditions, i.e., constant head as dictated by the elevation of the dam drainage gallery or constant flow rate induced by pumping. It is found that drainage wells are effective in reducing crack pressures and therefore uplift.

Measurements of Head Losses in a Subirrigation System

ABSTRACT THE head losses were measured in a subirrigation system on a sandy loam soil in southern Quebec during the Summer of 1985. The measurements included entrance head loss from a control chamber, friction head loss in drain pipes, exit head loss from perforations in the pipe and divergence head loss in the soil around drain pipes. The head losses were found to be a function of the flowrate in the subirrigation system. For the experimental setup, total head losses were found to be about 55 cm for an average water inflow of 30 L/min in the control chamber. It was found that the exit head loss from perforations in pipes is the most significant head loss in the subirrigation system. It was 75% of the total head loss in the subirrigation system.