Thesis (M.Phil.)--University of Waikato, 2006. / Includes bibliographical references (leaf 89)

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This thesis describes a short study to examine the behaviour of submerged flow over a thin plate weir with differing upstream and downstream bed levels i.e. an unequal bed weir as opposed to an equal bed weir where the upstream and downstream beds are at the same level. As submerged weir flow is a function of downstream conditions, it was thought that a lower downstream bed would make submerged flow over the weir easier, This is turn suggested that; The shape of the upstream head (Hu) vs downstream head (Hd) graph would change, being initially more steep in the unequal bed case. The Froude Number of the approaching flow would be lower for the unequal bed weir than for an equal bed weir at the same submergence. Using one of the existing submerged flow formula would lead to an erroneous calculated value. A series of measurements was done on two model weirs of different sizes subject to successive levels of submergence. Analysis of the readings of upstream and downstream heads indicated that the difference in bed levels was significant and the three effects above were noted. The work also suggested a new form of equation to calculate flow over a submerged weir. This was looked at briefly.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science in Engineering Johannesburg, 2017 / South Africa is a water scarce country and dams play a large role in the infrastructure of our country by providing water for many purposes. With the growth of the country, new dams are needed and existing dams require rehabilitation. Often, increasing a spillways capacity forms part of the rehabilitation required at dams. Therefore, one of the main aims of this study is to look at an option for increasing a spillways discharge capacity. The labyrinth and Piano key weirs (PKW) were investigated together with a combination of the two spillway types. Different geometric attributes were combined and varied to develop a new design that would assist in improving discharge capacity while reducing the cost, producing an economically viable option. Thirty five physical models were built and tested in this regard. Comparison was made with the standard PKW design in terms of discharge capacity, hydraulic efficiency, length ratio (L/W) and cost related to concrete volume required. It was concluded that efficiency, discharge capacity and cost can be improved with this new combined design however more geometric variations need to be studied to ascertain these results. / MT 2018

Oblique weirs are those weirs placed at an angle with respect to the channel centerline. They can be used in canal applications where more discharge is needed, but there is limited freeboard. The discharge coefficients were determined for 54 different weirs by measuring total head for various flows over each weir. These weirs included sharp, half round and quarter-round-crested weirs. There were 18 weirs for each crest shape with three weir heights for each angle tested. The oblique angles tested were 10°, 15°, 25°, 45°, 60°, and 90° with respect to the channel centerline, with the nominal weir heights being 4, 8, and 12 inches. The half-round-crested weirs were the most efficient, followed by the quarter-round-crested weirs and the sharp-crested weirs were the least efficient. By decreasing the oblique angle, the weir length became longer and the weir would be more efficient than the normal weir.

Installation of low-grade weirs in agricultural drainage ditches is being evaluated as an innovative, and cost effective, management practice that decreases nutrient concentrations and loads by increasing water volume and hydraulic residence time of the ditch. Results revealed that weirs significantly increased (P = 0.029) hydraulic residence time (HRT) and ditch water volumes, leading to considerable reductions in outflow water volumes (61%). Furthermore, ditches with weirs achieved greater (P = 0.09) cumulative outflow load reductions (96%) and greater (P = 0.029) concentration reductions during the biogeochemical reduction phase of the experiment. Similarly, field research from Terrace Ditch in Yazoo County, MS yielded significant percentage concentration reductions for baseflow (53%), stormflow (63%), and load (65%). Results from the experimental approach and field scale research offer promising insight into the future of low-grade weir’s establishment as an additional best management practice in agricultural landscapes.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: The compound sharp-crested weir, which consists of two or more notches at different elevations, is the most common type of flow gauging structure found in South Africa. The Department of Water Affairs and Forestry (DWAF) is responsible for the operation of these weirs. They are currently experiencing the following problems regarding flow measurement with compound sharp-crested weirs: 1. During free-flow conditions, also known as modular flows, there is uncertainty about the accuracy of the discharge formulas. Although reliable formulas exist for single notch weirs, it is not clear how they should be modified for compound weirs. Whilst methods have already been developed to deal with compound weirs their accuracy needs to be investigated further. 2. When the weirs become submerged during floods, the upstream water head is affected by downstream water levels and the original formulas are not applicable. It has so far been impossible to calculate discharge accurately under these so-called non-modular flow conditions. This report summarises the findings of an extensive study which addressed the issues mentioned above. A comprehensive test programme was completed during which variations of compound sharp-crested weirs were tested under both modular and non-modular flow conditions. In the development of new methods care was taken to adhere to internationally accepted standards. This should make South African practice acceptable to others. One important characteristic of compound weirs is the presence of end contractions. It was found that they have a significant effect on discharge measurement. Generally, the more a weir is contracted, the lower its coefficient of discharge becomes. It was also established that end contractions can ensure excellent aeration for compound weirs. For modular flow conditions it was possible to develop a discharge formula based on the IMFf equation, which is included in the ISO standards. This new method was found to produce the smallest errors when compared to other existing formulas (average error 0.6%). During non-modular flow conditions it was noted that end contractions also play an important role, at least during the early stages of submergence. In full-width weirs the upstream water level tends to drop first (due to de-aeration) before it rises again with increasing submergence. Weirs with end contractions do not suffer from this problem. It was further established that the effect of submergence could be described in terms of an energy loss occurring at the drowned weir. This energy loss is a function of the velocities at the so-called vena contracta of the weir and at the downstream river cross section. As the difference between these velocities increases, the energy loss increases as well. Two methods were tested to estimate the discharge under submerged conditions. The Villemonte formula works well if the energy losses at the weir are relatively high, while the Wessels method is reliable if the energy losses become smaller. A procedure was developed which indicates when each method is applicable. The test data indicated that the maximum error is up to ±10% at high submergence ratios (S> 0.80) if this procedure is followed. / AFRIKAANSE OPSOMMING: Multikeep-skerpkruinmeetstrukture bestaande uit twee of meer kepe op verskillende vlakke word meestal gebruik om vloeie in Suid-Afrikaanse riviere te meet. Die Departement van Waterwese en Bosbou (DWAF) is verantwoordelik vir die instandhouding van sulke meetstrukture. Hulle ervaar tans die volgende probleme met vloeimeting by multikeepskerpkruine: 1. Gedurende modulêre (onversuipte) toestande bestaan daar nog onsekerheid oor die akkuraatheid van die formules wat gebruik word om vloeitempo's te bereken. Alhoewel betroubare formules ontwikkel is vir enkelkepe, is dit nie duidelik hoe hulle aangepas kan word sodat hulle ook vir multikepe gebruik kan word nie. Die akkuraatheid van sommige bestaande metodes vir multikepe moet ook ondersoek word. 2. Onder versuipte toestande word die stroom-op watervlak beïnvloed deur die stroom-af watervlak en die formules vir vry-vloei toestande is nie geldig nie. Dit was tot nou toe nie moontlik om vloeitempo ' s akkuraat te bereken onder hierdie nie-modulêre toestande nie. Hierdie verslag bied 'n opsomming van die bevindinge van 'n navorsingsprojek wat bogenoemde probleme aangespreek het. 'n Toetsprogram is uitgevoer wat moontlike konfigurasies van multikepe ingesluit het. Die modelle van die meetstrukture is onder beide vry-vloei en versuipte toestande bestudeer. Gedurende die ontwikkeling van nuwe formules vir die berekening van vloeie is daarna gestreef om so veel as moontlik gebruik te maak van internasionale standaarde. Dit behoort Suid-Afrikaanse praktyke vir andere aanvaarbaar te maak. 'n Belangrike eienskap van multikepe is die voorkoms van end-kontraksies. Hulle het 'n groot invloed op vloeimeting en oor die algemeen het 'n keep met groot end-kontraksies 'n laer vloei koëffisient as 'n vol-wydte keep. End-kontraksies is ook baie effektief om skerpkruine te belug. Vir vry-vloei toestande is gevind dat 'n metode gebaseer op die IMFT vergelyking (ingesluit in ISO standaarde) baie goeie resultate lewer. In vergelyking met ander bestaande metodes gee dié metode die kleinste foute met 'n gemiddelde fout van 0.6%. Onder versuipte toestande speel end-kontraksies ook 'n belangrike rol, ten minste by beperkte versuiping. As vol-wydte kepe beskou word, kan gesien word dat die stroom-op watervlak eers daal voordat dit weer styg (weens ontlugting). Kepe met end-kontraksies ly nie aan hierdie probleem nie. Dit is verder bevestig dat versuipte toestande beskryf kan word in terme van 'n energie verlies wat by die versuipte meetstruktuur voorkom. Hierdie energie verlies is 'n funksie van die snelhede by die vena contraeta van die keep en by die stroom-af rivier snit. As die verskil tussen die twee snelhede groot is, is die energie velies ook groot. Twee bestaande metodes vir versuipte toestande is getoets. Villemonte se vergelyking werk goed as die energie verliese groot is, terwyl Wessels se metode beter werk as die verliese klein raak. 'n Prosedure is ontwikkel wat dit moontlik maak om die regte metode te kies vir 'n spesifieke toestand. Vanaf die toetsdata is bepaal dat die maksimum fout ±10% is by hoë grade van versuiping (S> 0.80) wanneer bogenoemde prosedure gevolg word.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: As part of a previous WRC project, three types of sluicing flumes were developed for use in compound weirs in combination with sharp-crested and crump weirs, (Rossouw et al., 1998). These sluicing flumes have several advantages which make them ideal structures for flow measurement in South African rivers. These are a high modular limit, stable modular flow characteristics, an ability to measure a wide range of flows accurately, as well as good sediment handling characteristics. These three flumes have been calibrated under modular or free flow conditions in combination with sharpcrested and crump weirs. There is a high degree of variability of flow in South African rivers. Flood discharges are part of this variability, and can form an important part of the mean annual runoff. Measuring weirs cannot always be built so that they do not become submerged during floods, but it is nevertheless important that flood discharges be recorded. It is therefore important that these compound weirs be calibrated for flow measurement under non-modular or submerged conditions. The purpose of the research undertaken for this WRC project is to find a method to calculate the non-modular discharge over compound weirs consisting of sluicing flumes in combination with sharp-crested and crump weirs. By analysis of existing data from the previous WRC project, as well as data from laboratory tests undertaken as part of this project, the submergence effect of sluicing flumes has been quantified. A range of configurations of sharp-crested weirs as well as crump weirs in combination with the sluicing flume have been tested. A new method has been developed to calculate the submerged discharge over these compound weirs. This method is suitably accurate, and can be recommended to the DWAF for use. The calculation procedure that must be followed in order to calculate the submerged discharge over these compound weirs becomes rather complicated due to the iterations that must be carried out. In order to clarify these procedures, flow charts are provided which set out the steps that must be followed. Calibration curves for all the combinations of compound weirs analysed in this report are also provided. These can be used to obtain estimates of the discharge in the field, and can also be used as a check on any calculations carried out. The principal goal of this project, namely that of finding a suitably accurate method to calculate the non-modular discharge over these compound weirs has therefore been achieved. / AFRIKAANSE OPSOMMING: As deel van 'n vorige Water Navorsings Kommisie (WNK) projek, is drie spoelgeute ontwikkel vir gebruik in saamgestelde meetwalle in kombinasie met skerp-kruin en Crump oorlope, (Rossouwet al., 1998). Die spoelgeute het eienskappe wat hulle gunstig maak vir vloeimeting in Suid Afrikaanse riviere. Vanhierdie eienskappe is 'n hoë modulêre limiet, stabiele modulêre vloei eienskappe, goeie sediment hanterings eienskappe en 'n vermoë om oor 'n wye bereik vloeie akkuraat te kan meet. Hierdie drie geute is in kombinasie met skerpkruin en Crump oorlope gekalibreer onder vryvloei toestande. Vloeie varieër baie in Suid Afrikaanse riviere. Vloede is deel van hierdie variasies en maak 'n belangrike deel uit van die gemiddelde jaarlikse afloop. Meetwalle kan nie altyd gebou word sodat hulle nie versuip tydens vloede nie, maar dit is nogtans belangrik dat hierdie vloeie gemeet word. Daarom is dit belangrik dat saamgestelde meetwalle gekalibreer is vir vloeimeting onder versuipte of nie-modulêre toestande. Die doel van die navorsing wat gedoen is vir hierde WNK projek was om 'n geskikte metode te ontwikkel om die nie-modulêre vloeie oor saamgestelde meetwalle, wat bestaan uit spoelgeute in kombinasie met skerpkruin en Crump oorlope, te kan bereken. Met die analise van bestaande data van die vorige WNK projek, asook data van labratoriumtoetse wat gedoen is as deel van hierdie projek, is die versuiping van spoelgeute beskryf. 'n Hele reeks skerpkruin asook crump oorlope is getoets in kombinasie met die spoelgeute. 'n Nuwe metode is ontwikkel om die nie-modulêre vloei oor hierdie saamgestelde meetstrukture te kan bereken. Hierdie metode IS akkuraat genoeg om aan die Departement van Waterwese te kan aanbeveel. Die berekingsproses wat gevolg moet word om die versuipte vloei oor die saamgestelde meetstrukture te bereken, raak ingewikkeld as gevolg van die iterasies wat uitgevoer moet word. Vloeidiagramme is opgestel wat hierdie prosedures duidelik uiteensit. Kalibrasie kurwes is ook ontwikkel vir al die kombinasies van saamgestelde meetwalle wat geanaliseer is in hierdie verslag. Hierdie kurwes kan gebruik word om skattings te maak van vloeie in die veld, maar ook om enige berekings wat gedoen is te kontroleer. Die hoofdoel van hierdie projek, naamlik om 'n geskikte metode te ontwikkel wat die nie-modulêre vloeie oor saamgestelde meetwalle akuraat kan bereken, is bereik.

The Utah Water Research Laboratory, in conjunction with the State of Utah, initiated a study to determine the accuracy of a wide variety of flow measurement devices in Utah. The project selected 70 sites with flow measurement devices throughout the state. During the assessment each device had its physical condition and flow measurement accuracy documented. Although a wide variety of flow measurement devices were tested, the majority were Parshall flumes. Many of the assessed Parshall flumes were not measuring flow to the specified ±5 percent design accuracy. Problems in flow measurement were due to issues with the staff gauge location and incorrect entrance geometry. Laboratory tests were conducted at the Utah Water Research Laboratory in an attempt to provide accurate flow measurement from flumes with these issues. The tests simulated incorrect locations for measuring upstream head with different entrance geometries on a 2-ft-wide Parshall flume. The flume was tested with three different entrance wingwall configurations, eighteen stilling wells, and two point gauges, allowing water surface profiles to be collected throughout the flume. Corrections for incorrect head measurement locations and entrance geometries were created. The objective of this thesis is to provide water users and regulators with the information necessary to help improve open-channel flow measurement accuracies. An overview of design accuracies and flow measurement devices is given. In addition, a method to correct for incorrect head readings in Parshall flumes, a widely used flow measurement device in Utah, is presented. It is expected that this information will help water users and regulators monitor their water with the understanding necessary to ensure that water is more accurately measured.

Thesis (Ph.D.)--University of Oregon, 2002. / Adviser: Jon M. Erlandson. Includes bibliographical references.