Water Conveyance System Research Articles

Experimental study of air delivery into water-conveyance system of the radial-axial turbine

The paper presents an experimental study of oscillatory response in the Francis turbine of hydraulic unit. The experiment was performed on large-scale hydrodynamic test-bench with impeller diameter of 0.3 m. The effect of air injection on the intensity of pressure pulsations was studied at the maximum pressure pulsations in the hydraulic unit. It was revealed that air delivery into the water-conveyance system of the turbine results in almost two-fold reduction of pressure pulsations.

Extreme hydrological changes in the southwestern US drive reductions in water supply to Southern California by mid century

The Southwestern United States has a greater vulnerability to climate change impacts on water security due to a reliance on snowmelt driven imported water. The State of California, which is the most populous and agriculturally productive in the United States, depends on an extensive artificial water storage and conveyance system primarily for irrigated agriculture, municipal and industrial supply and hydropower generation. Here we take an integrative high-resolution ensemble modeling approach to examine near term climate change impacts on all imported and local sources of water supply to Southern California. While annual precipitation is projected to remain the same or slightly increase, rising temperatures result in a shift towards more rainfall, reduced cold season snowpack and earlier snowmelt. Associated with these hydrological changes are substantial increases in the frequency and the intensity of both drier conditions and flooding events. The 50 year extreme daily maximum precipitation and runoff events are 1.5–6 times more likely to occur depending on the water supply basin. Simultaneously, a clear deficit in total annual runoff over mountainous snow generating regions like the Sierra Nevada is projected. On one hand, the greater probability of drought decreases imported water supply availability. On the other hand, earlier snowmelt and significantly stronger winter precipitation events pose increased flood risk requiring water releases from control reservoirs, which may potentially decrease water availability outside of the wet season. Lack of timely local water resource expansion coupled with projected climate changes and population increases may leave the area in extended periods of shortages.

Hysteresis Characteristic in the Hump Region of a Pump-Turbine Model

The hump feature is one of the major instabilities in pump-turbines. When pump-turbines operate in the hump region, strong noise and serious fluctuations can be observed, which are harmful to their safe and stable operation and can even destroy the whole unit as well as water conveyance system. In this paper, a low specific speed (nq = 36.1 min−1) pump-turbine model was experimentally investigated. Firstly, the hump characteristic was obtained under 19 mm guide vane opening conditions. More interestingly, when the hump characteristic was measured in two directions (increasing and decreasing the discharge), characteristic hysteresis was found in the hump region. The analysis of performance characteristics reveals that the hump instability is the result of Euler momentum and hydraulic losses, and different Euler momentum and hydraulic losses in the two development processes lead to the hysteresis phenomenon. Then, 12 pressure sensors were mounted in the different parts of the pump-turbine model to obtain the time and frequency characteristics. The analysis of the corresponding fast Fourier transform confirms that the hump characteristic is related to low-frequency (0.04–0.15 times rotational frequency) vortices. The occurrence and cessation of vortices depend on the operating condition and measurement direction, which contribute to the hysteresis feature. Finally, the type of the low-frequency vortices was analyzed through the cross power spectrum.

Hydraulic characteristics of a siphon-shaped overflow tower in a long water conveyance system: CFD simulation and analysis

The siphon-shaped overflow tower is a new type of pressure-suppressing structure used in long water conveyance systems, and it plays a crucial role in guaranteeing the system's stability and safety during hydraulic transient processes. The flow in the tower is characteristic of weir flow in a closed duct, and is thus a complex air-water two-phase flow. Intensive studies of the flow patterns, the pressure pulsations, and the discharge capacity are necessary for better understanding of the flow processes and for the purpose of design. In this paper, we simulate the flow in a siphon-shaped overflow tower under both steady and unsteady flow conditions. Through a steady-flow field simulation, the relationship between the overflow discharge and the pressure in the connected pipeline is analyzed and an empirical formula for evaluating the discharge capacity is provided. Through a transient-flow field simulation, the negative-pressure distributions on the weir crest, the pressure pulsations on the crest and in the falling pond, and the transformation of the air-water two-phase flow in the downstream outlet pipe are analyzed. Moreover, the major influencing factors of the flow patterns, especially, the sectional area of the air vents, are clarified. It is indicated that the siphon-shaped overflow tower can regulate the pressure surge during hydraulic transients and guarantee the safety and stability of the pipeline system, if the shape and the vents are properly designed.

Looping Dynamic Characteristics of a Pump-Turbine in the S-shaped Region During Runaway

During transients, hydroturbines may demonstrate some dynamic characteristics that differ from the corresponding static characteristics in steady operating conditions. To study the dynamic characteristics of a pump-turbine, we simulated the runaway transients in a model pumped-storage plant by coupling one-dimensional (1D) water conveyance system and three-dimensional (3D) pump-turbine. The results show that the runaway dynamic trajectories form loops in the S-shaped region in the unit discharge and unit torque charts of the pump-turbine, not following the corresponding static characteristics. Theoretical analysis and flow patterns comparisons illustrate that the looping trajectories are mainly caused by the successive features of transient flow patterns, namely, the transient flows in the pump-turbine are influenced by their previous status. These features induce different performances between similar dynamic operating points in different moving directions. Furthermore, through comparing the transient parameters calculated by the dynamic and static characteristics separately, we found that both methods are available to capture the unstable behaviors of the pump-turbine, but the dynamic method displays more accurate results when simulating the critical transient parameters. Therefore, in practical engineering applications, we suggest to use the static characteristics method for stability analysis while dynamic characteristics method for transient parameters, which is important for optimizing the layout of water conveyance systems.

Comparison of Water Routing Computing Techniques

Comprehensive computational analysis was made for modelling the integrated hydrologic–hydraulics characteristics of varied unsteady flow in hydraulic structures as part of water engineering practices and river basin management. Several numerical skills, linear, non-linear, implicit, explicit methods were developed and tested with existing river analysis software of Danish Hydraulic Institute (DHI) and Hydrologic Engineering Centre (HEC) series models. Coupled hydrological and hydraulics analysis of storming run-off flows in broad waterway boundaries including flood plains of compound sections was performed. Application of models was encouraging, the complex water conveyance systems that transported lateral flows in natural rivers were modelled satisfactorily. Storming flow events in real rivers were coded and compared through different numeral techniques such as method of characteristics, Mac-Cormack, diffusive numeral model and Preissmann fully implicit model. Predicted results were close to observed values verified and confirmed the hand-written codes and programs in MATLAB environment. Enhanced modelling skills were justified by (HEC) series and Mike series computer software. Merits of this research were seen based on: numerical accuracy, consistency, stability and convergence results to observed targets.

An Experimental Investigation of Head loss through Trash Racks in Conveyance Systems

Trash racks are widely used in the water conveyance systems to prevent trappings of floating and submerged debris that would cause operational problems at downstream reaches. Head loss through the trash rack is one of the key parameters in designing trash racks. The trash racks commonly used in Sri Lanka are with circular bars. The existing methods to estimate head loss through these trash racks give very wide results which make it difficult for engineers to produce reliable designs for water conveyance systems. In order to investigate this problem in detail and to develop a methodology to estimate head loss through trash racks a set of experiments was performed in open channel with trash racks by considering the variable parameters such as bar diameter, clear spacing, inclination angle and unit discharge. In this study, a new head loss equation is proposed based on the experimental findings to estimate the head loss through trash racks made up of circular bars.

Flash flood water management practices in Dera Ghazi Khan City (Pakistan): a remote sensing and GIS prospective

Flash flood hazard of Wador hill torrent has distressed human activities in almost every part of Dera Ghazi Khan (D.G. Khan) City, Pakistan. In order to mitigate such hazards, and to utilize the flash flood water in such water-deficit area, the study identifies potential suitable sites for dam construction with quantitative assessment resulting in capacity determination of the designed dams. The developed methodology also incorporates the designing of downslope water conveyance system in storm water management model’s (SWMM) environment. The efficacy of the dams was analyzed using SWMM model’s runoff and transport module by integrating meteorological and topographic factors with the utilization of curve number method for runoff generation and modeling. Two sites were identified as suitable for dam construction with sufficient collective designed capacity of approximately 27 million m3 to store the flashy peaks. Number of channels designed results in systematic waterways to flow from the dam site to the outlet point (D.G. Khan Canal). The findings may be useful for mitigation strategies of the severe weather conditions. Similar integrated approach could be used for mitigation of flash flood around the world.

Uncertainty in the Analysis of Water Conveyance Systems

Conventionally, the design of water conveyance and distribution systems is based on the assumption that all the involved parameters are known a priori and remain unaltered throughout the life cycle of the system. This type of approach offers simplicity in the calculations by neglecting a variety of uncertainties which accompany the parameters and processes involved. However, significant uncertainties do appear during the analysis and design of these systems, such as the equivalent pipe roughness and the actual internal diameters of the pipes. Furthermore, the demands at the nodes of the system are dependent on several ambiguous assumptions which are not always met at the operation stage. To deal with these uncertainties, several mathematical data demanding approaches have been proposed in the past. In this study these uncertainties are incorporated in the analysis of the system, using the extension principle of the fuzzy sets and a new operation of the fuzzy subtraction. Based on the calculation of head losses for each branch of the system, the nodal heads are derived as fuzzy numbers. The proposed methodology, being a low data demand methodology, is illustrated by a numerical example of a water conveyance system.

Land subsidence in the San Joaquin Valley, California, USA, 2007–2014

Abstract. Rapid land subsidence was recently measured using multiple methods in two areas of the San Joaquin Valley (SJV): between Merced and Fresno (El Nido), and between Fresno and Bakersfield (Pixley). Recent land-use changes and diminished surface-water availability have led to increased groundwater pumping, groundwater-level declines, and land subsidence. Differential land subsidence has reduced the flow capacity of water-conveyance systems in these areas, exacerbating flood hazards and affecting the delivery of irrigation water. Vertical land-surface changes during 2007–2014 were determined by using Interferometric Synthetic Aperture Radar (InSAR), Continuous Global Positioning System (CGPS), and extensometer data. Results of the InSAR analysis indicate that about 7600 km2 subsided 50–540 mm during 2008–2010; CGPS and extensometer data indicate that these rates continued or accelerated through December 2014. The maximum InSAR-measured rate of 270 mm yr−1 occurred in the El Nido area, and is among the largest rates ever measured in the SJV. In the Pixley area, the maximum InSAR-measured rate during 2008–2010 was 90 mm yr−1. Groundwater was an important part of the water supply in both areas, and pumping increased when land use changed or when surface water was less available. This increased pumping caused groundwater-level declines to near or below historical lows during the drought periods 2007–2009 and 2012–present. Long-term groundwater-level and land-subsidence monitoring in the SJV is critical for understanding the interconnection of land use, groundwater levels, and subsidence, and evaluating management strategies that help mitigate subsidence hazards to infrastructure while optimizing water supplies.

Water Works Through Four Millenia in Turkey

Turkey is one of the foremost open-air museums of the world with regard to historical water works from the last 4000 years. Some of them are still in operation after several centuries or even several millennia. There are remains of dams, irrigation canals, and water collection structures dating back to the IInd millenium BC, the Hittite period in Central Anatolia. Several dams, irrigation canals, qanats date back to the first half of the Ist millenium BC, the Urartu period in Eastern Anatolia. Long-distance water conveyance systems, pipes, masonry canals, inverted siphons, tunnels, dams date back to the second half of the Ist millenium BC and the Ist millenium AD, the Hellenistic, Roman and Byzantine periods in Western and Southern Anatolia. Some dams, canals, watermills date back to the 11th to 14th centuries, the Seljukide period in Central and Eastern Anatolia. Several dams, irrigation canals, long distance water conveyance systems date back to the 14th to early 20th centuries, the Ottoman period in Turkey. Based on this tradition from four millenia, the modern Republic of Turkey, founded in 1923, is continuing to develop her water resources. The South-eastern Anatolia Project, encompassing the Euphrates-Tigris basin in Turkey, is the most interesting example.

Water conveyance and on-farm irrigation system efficiency gains in southern Alberta irrigation districts from 1999 to 2012

Efficiency gains from on-farm irrigation system upgrades and canal rehabilitation in southern Alberta irrigation districts are influenced by weather variability. The Irrigation Demand Model was used to estimate differences in on-farm demand and conveyance losses based on irrigation district characteristics in 1999 and 2012 using weather data from 1928 to 2012. Monte Carlo simulations were subsequently performed to determine the magnitude of potential efficiency gains at different chances of exceedance. Changes in irrigation systems and water conveyance infrastructure reduced gross demand by 74 mm from 1999 to 2012, with a 55-mm reduction in on-farm demand and a 19-mm decrease in conveyance losses at a 10% chance of exceedance. Reductions in gross demand on a volume basis from 1999 to 2012 ranged from 170 to 200 million m3, even with about 30,300 ha of irrigation expansion. Conveyance loss reductions were stable at about 50 million m3, so 70 to 75% of the potential water savings were achieved through reduced on-farm demand. Mean seasonal naturalized flows available for use in southern Alberta from 1912 to 2009 ranged from 2.08 billion m3 in high-demand years to 3.95 billion m3 in wet years. Gross demand based on irrigation district characteristics in 2012 varied from 1.73 billion m3 in wet years to 2.83 billion m3 in high-demand years. Additional gains in efficiency from on-farm irrigation system upgrades and rehabilitation of conveyance infrastructure in the future will help mitigate the increased risk of water scarcity as irrigation districts expand with current licensed water allocations.

English

Irrigation water pricing has been considered as a tool to enhance water conservation in irrigated agriculture. We have evaluated the effects of water pricing on water management practices in Awash Basin Authority (ABA). The water charge has been collected over years with the aim to generate money for the Awash Basin Authority to cover operational expenses. Both the authority and water users see the charges paid as the contribution than as water demand management tool. Widespread irrigation inefficiency and low performances are more due to low level of irrigator’s knowledge to manage water, poor water conveyance and distribution systems, public ownership over large and medium-scale irrigation schemes, and inability to measure and control water. Increasing water price under such service conditions will only add burden to farmers and unlikely to be feasible. Despite these poor water delivery services, users are willing to pay relatively more than they currently pay which could increase the income of the basin authority. Improvement in irrigation water management requires strengthening of irrigation research and extension services, building the capacity of irrigators, and improving irrigation system operation and maintenance services.   Key words: Irrigation, water pricing, irrigation performance, willingness to pay.   &nbsp

Reliable Solution in Dynamic River Flow System Computations

Reliable Solution in Dynamic River Flow System Computations Application and limitation of various computational methods handling hydrologic runoff and varied unsteady river flow equations was studied here. Investigations were focused on many numerical aspects linear, non-linear solution of continuity and dynamic equations. A river catchment was examined, hydrometric stations, water control measures at upstream and hydrodynamic systems of river- reservoir at downstream were modeled provided evaluation and performance of water conveyance systems proposed for water resources planning and management. Application of modeling flow discharge in rivers was reviewed through a number of flow routing techniques. These classical computational methods have been widely used in water resources engineering and are subject of front line research by hydrologic and hydraulic modelers. Application of conventional and practical methods such as Muskingum-Cunge which are classified under hydrologic and hydraulic routing categories was examined for nonlinear variation of hydrodynamic parameters. Several methods including various numerical schemes were used and compared for modeling accurate unsteady flows computations. Analysis were ranked based on four criterions (consistency, stability, convergence and accuracy) examined with field observations and recorded data. Result of analysis verified that with careful description of constant and variable parameters involved in the Muskingum-Cunge model, the nonlinear terms and physical behavior of the problem was best fitted as compared by developed numerical solutions. The kinematic wave model and Hydrologic Engineering Centre (HEC) and Danish Hydraulic Institute (DHI) Mike series software were employed to verify developed fully dynamic wave model. A 42 kilometer reach length (a location between two hydrometric stations) was modeled with hydrologic and hydro-informatics parameters in Kor River were used. Comparing performances of two constant and variable Muskingum-Cunge methods, nonlinear model with variable parameters had highest reliability and accurately was used for dynamic water wave routing in water conveyance systems (especially for rivers without measuring gage stations).

Development of rectangular broad-crested weirs for flow characteristics and discharge measurement

One of the important problems which designers and engineers are faced with is proper measurement of water flow rates in open channels and rivers. To solve this problem, the water discharge to be precisely measured in water conveyance systems such as off takes and distribution ditches. The common procedure to meet this requirement is achieved by using water-measuring structures such as flumes, orifices, weirs and current meters. Among the mentioned structure, engineers prefers the weirs because of their simple structure and economical features. The broad-crested rectangular weirs are very common which are widely used in water ways and canals. In this study, the effect of steeping in the upstream side of rectangular broad-crested weirs over discharge coefficient and flow characteristics is investigated. Five weirs with 15, 30, 45, 60 and 90 weir angles were developed and flow discharge coefficient, negative velocity over the weir crest edge and water surface profiles along the weir crest evaluated in laboratory hydraulic flume. The obtained results showed by decreasing the slope of the upstream side, discharge efficiency and the discharge capacity of the weir are increased subsequently. Consideration of experimental data it is obvious that by using the proposed weir with slope of 15 degree in comparison with standard weir, the efficiency is increased up to 19.17%. It is noteworthy that by reducing the slope, return current on the crest is not observed.

Evaluation of urban growth effects on surface runoff using SCS-CN method and Green-Ampt infiltration model

Evaluation of land cover/use change and its impact on hydrological design aspects plays a vital role in assessing the capacity of existing storm water conveyance systems and its capability towards the anticipated peak flow. This paper attempts to illustrate an application of Soil Conservation Service (SCS-CN) method for runoff estimation using continuous time series rainfall. And also, the present work proposes a Land use factor based on the Curve Number to correct the infiltration rate according to the prevailing land cover/use. Indian remote sensing (IRS) satellite data for the years 1989, 1992, 1995, 1998, 2001, 2004, 2007, and 2010 are used to evaluate the growth of Tiruchirapalli city, India city and to assess its impact on surface runoff. The Geographical information system (GIS) is used to prepare the different layers belonging to various land covers identified from remotely sensed data. The sub-watersheds are created using Digital Elevation Model (DEM) prepared by ARC GIS software. The single storm event and 50-year return period rainfall data are used as a hydrological input to the model to evaluate the increase in runoff over the years due to change in the land cover of the study area. The study reveals that the impact of land cover/use change is more significant for longer duration storm than short duration storm at the same magnitude. Further, it is noticed from the study that the runoff depth and runoff co-efficient is large for short duration rainfall than long duration rainfall at the same magnitude.

Rainwater Collection and Management from Roofs at the Edison Environmental Center

AbstractIn the past, the U.S. Environmental Protection Agency Edison Environmental Center, a 80.9-ha (200-acre) federal-run facility, directed all rainwater from roofed areas to the existing storm water conveyance system. Over the last several years, modifications have been made to the practice of discharging storm water to the existing conveyance system due to federal mandates. Roof runoff from approximately 0.28 ha (0.69 acre) has been directed to bioinfiltration units to infiltrate into the ground, while rainfall from another 0.14 ha (0.34 acre) is being captured and used for nonpotable purposes. This paper discusses the water quality of the roof runoff directed to the bioinfiltration units and the reductions in usage of potable water due to a rainwater capture system. The mean pollution concentrations of the roof runoff were for the most part below drinking water standard levels. An exception was antimony because mean concentrations were over the drinking water standards; the primary source of contami...

A geochemical perspective on Parisian urban history based on U–Th dating, laminae counting and yttrium and REE concentrations of recent carbonates in underground aqueducts

Two laminated carbonate deposits from the wall of an underground aqueduct, built between the 13th and 15th century, in Paris, France, were studied to provide historical information about nearby human occupation and urban development. To obtain a robust chronology for these small (29 and 45 mm thick) and very young deposits (< 800 a based on the probable date of aqueduct construction), we adopted two methods: laminae counting and U–Th analysis. For laminae, we tested the hypothesis that their deposition is bi-annual. Concerning U–Th dating, the influence of inherited 230Th on calculated ages is discussed and detrital 230Th/232Th values for each speleothem was determined using stratigraphic constraints and found to be significantly different despite their close proximity. In these speleothems, that precipitated over approximately 300 a according to U–Th dating, the number of laminae is similar, and two laminae were deposited each year. The lamina-counting chronology was used to interpret the rare earth elements and yttrium content (REE + Y) variations measured by ICP-QMS as historical variations in water quality in relation with the anthropogenic use of these elements. There is a marked increase of the REE + Y concentrations since the second half of the twentieth century. A marked negative Ce anomaly in the NASC-normalized REE trend is evidenced, and is more pronounced for post 1850s. This anomaly could be due to prior precipitation of Ce4+ before the water reached the aqueduct, related to a high organic matter content of the water in oxidizing conditions. The increase in the Ce anomaly could indicate a second source of water, from a wastewater collection system or a modern water conveyance system. We thus demonstrate the interest of using these annual carbonate deposits in urban areas as a proxy for the history of urbanization or human activities.

Hydraulic capacity of ancient water conveyance systems to Ephesus

Ephesus was supplied by several long-distance water conveyance systems in ancient times. The 8 km long Şirince water conveyance system consists of baked clay pipes, and had a hydraulic capacity of around 10 l/s. The 7 km long Derbentdere water conveyance system consists also of baked clay pipes; and its hydraulic capacity was around 20 l/s. The 36 km long Değirmendere water conveyance system is a masonry conduit; its hydraulic capacity was around 200 l/s. The 42 km long Kayapınar water conveyance was also a masonry conduit; its hydraulic capacity was around 100 l/s. The Şirince system was extended over to the Ayasuluk hill and Saint John basilica in the 6th century ad by the 650 m long Selcuk aqueduct, serving as the venter of an inverted siphon.

Assessing the impact of urbanization on storm runoff in a peri-urban catchment using historical change in impervious cover

his paper investigates changes in storm runoff resulting from the transformation of previously rural landscapes into peri-urban areas. Two adjacent catchments (∼5 km2) located within the town of Swindon in the United Kingdom were monitored during 2011 and 2012 providing continuous records of rainfall, runoff and actual evaporation. One catchment is highly urbanized and the other is a recently developed peri-urban area containing two distinct areas of drainage: one with mixed natural and storm drainage pathways, the other entirely storm drainage. Comparison of observed storm hydrographs showed that the degree of area serviced by storm drainage was a stronger determinant of storm runoff response than either impervious area or development type and that little distinction in hydrological response exists between urban and peri-urban developments of similar impervious cover when no significant hydraulic alteration is present. Historical levels of urbanization and impervious cover were mapped from the 1960s to the 2010s based on digitized historical topographic maps and were combined with a hydrological model to enable backcasting of the present day storm runoff response to that of the catchments in their earlier states. Results from the peri-urban catchment showed an increase in impervious cover from 11% in the 1960s to 44% in 2010s, and introduction of a large-scale storm drainage system in the early 2000s, was accompanied by a 50% reduction in the Muskingum routing parameter k, reducing the characteristic flood duration by over 50% while increasing peak flow by over 400%. Comparisons with changes in storm runoff response in the more urban area suggest that the relative increase in peak flows and reduction in flood duration and response time of a catchment is greatest at low levels of urbanization and that the introduction of storm water conveyance systems significantly increases the flashiness of storm runoff above that attributed to impervious area alone. This study demonstrates that careful consideration is required when using impervious cover data within hydrological models and when designing flood mitigation measures, particularly in peri-urban areas where a widespread loss in pervious surfaces and alteration of drainage pathways can significantly alter the storm runoff response. Recommendations include utilizing more refined urban land use typologies that can better represent physical alteration of hydrological pathways.