Üniform su almayı sağlayan yansavakların tasarımı

Abstract

Bu çalışma, bir sulama kanalı boyunca kanal kenarına yerleştirilen yansavakl ardan, sulanacak bölge için yeterli miktarda ve eşit şekilde su alınmasını sağlayacak kanal ve yansavakların projelendirme şekli hakkındadır. Bir çok sulama bölgesinde büyük ana kanallar ve su alma yapıları inşa edilmesine rağmen bütün sulayıcılara sulama suyunun istenilen miktarda ve zamanında erişemediği bir gerçektir. Bunun nedeni, gösterişli büyük barajların ve sulama kanallarının planlanmasına büyük önem verilmesine karşılık sulama projelerinin su dağıtım tekniği yönünden yetersiz planlanması ve su dağıtımında büyük önem taşıyan su alma ağızlarına planla mada hiç önem verilmemesi veya kaba yaklaşımla boyut lan- dırı İması olduğu söylenebilir. Bu durum yetersiz ve ada letsiz bir su dağıtımı yanında büyük su israfına neden olmaktadır. Sulama şebekelerinde sulama suyunun dağıtımı, su miktarını ve su seviyesini düzenlemek suretiyle gerçek leştirilebilir. Bu çalışmanın birinci bölümünde, kenarında bir yan- savak bulunan bir açık kanaldaki akımın özellikleri, genel hesap esasları ve uygulanan tertip şekilleri hakkında bir takım faydalı bilgiler verilmiştir. İkinci bölümde, yansavaklarla ilgili yapılmış olan çalışmalar hakkında özet bilgiler aktarılmıştır. Üçüncü bölümde, öncelikle incelenecek problem tanı tılmıştır. Sonra laboratuvarda mevcut kanal içine bir deney kanalı inşa edilmiş ve daraltma faktörü esas para metre olarak seçilerek deneysel çalışmalar yapılmıştır. Deney ölçüm değerleri ve bunlara ait hesap sonuçları da bu bölümde verilmiştir. Çalışmanın dördüncü bölümünde deney sonuçlarının değerlendirilmesi yapılmış ve gerekli öneriler sunulmuştur.

This study is about lateral weir which is set up along the canal which ensures obtaining sufficient and equal amount of outflow from the canal by defining optimum canal shape. In our everyday life, water, being one of the few resources, is getting its significant continiously. Due to rapid population increase and rising of life standarts, intake and planning foundation in many parts of the world are obliged to distribute limited water potential in a bit more rational fashion and to use its work up tecnique in a best way. Inspite of irrigation of large main canals and contraction of intake, its a fact that irrigators do not get the necessary amount of water and the supply does not reach in time. Because of this, irrigation projects water distribution techniques may have inadequate planning and no importance to water inlets planning which is important in water distribution or approximate approach to designing. In this situation, besides inadequate and unequal water distribution, a big loss results as well. In the sense of improving water distribution of a network, all the problems arising in the distribution of water through a canal network in a desired manner may be understood. Distribution of water through water canals, water quantity and water levol can be nchlvod in an adjusted way. Water level from point of view of water distribution In canals having adjusted water level get a great importance. Due to the function of outflow, the water level in the open canals having free surface flow, by the irrigator regulators it is possible to adjust the quantity of water. In this text, test data related to uniformly discharging lateral weirs are presented. Uniform weir outflow conditions were obtained by altering the geometric parameters of weir system. The outflow through the lateral weir model was obtained on the basis of the hydrodinamic model. -xiii- In the first chapter, some useful knowledge about the characteristics of flow in open canal with lateral weir on the side of canal, basic calculation rules, and apl icat ion of designed shapes are presented. Due,to complexity of flow and outflow in the vicinity of lateral weir, no definite solution is found till now. Because of this, investigators have made experimental studying and have researched about lateral weirs problem by means of some assumptions or theortical studies. We must know that the lateral weirs are short in size. Otherwise, due to secondary flow which occurs along the lateral weir and other energy loss, constant energy level idea is wrong. During the test, the energy level of fluid along lateral weir is assumed constant. Because of different flow regimes in the free canals and changing in flow depth at the end of lateral weir acording to the critical depth, water surface profiles occur in different shapes along lateral weir. The relation between quantity of water which flows through canal with a constant energy level and depth of water can be explained by "KOCH PARABOLA". If the flow depth at the beginning of lateral weir is higher than critical depth (subcritical regime), then the flow depth in the main canal increases along lateral weir. After that swelling which occurs at the end of lateral weir decreases towards end of the canal and becomes equal to the critical depth. If the flow depth at the beginning of lateral weir is lower than critical depth (supercritical regime), then the flow depth in the main canal decreases along lateral weir. Next, flow depth increases from at the end of lateral weir and reaches to a uniform flow depth. The lateral weirs may be constructed parallel to the canal axis or at a definite angle. In practice, usually, it is constructed in a manner in which weir crest is parallel to the canal floor. Sometimes, the lateral weir may be set up at a positive or negative slope acording to the canal floor. Designed shape of the lateral weir affects output (discharge capacity). On the other hand, the profile of weir crest may be plain, sharp crested or lifted nappe form. Sharp crested profiles are applied on the models and small foundations. The studies about lateral weirs have been started at the end of 19. th century. Preliminary studies were usually experimental and as a result of these, some -XIV- emprical formulas developed that are still used in practice. In the course of time, investigates started theoretical studying, and theoretical results were compared with experimental studies. In these experimental studies, rectangular sectional canals were used more. After that, theoretical analysis were developed by considering rectangular section. In the first chapter: First of all, lateral weir problem was explained. After that, conditions of obtaining irrigation water from uniform elevation by use of lateral weirs contructed at specified intervals along the canal of vertical profile where water flows in subcritical regime, were studied experimentally. Theoretical approaches were expressed firstly, and experimental studies carried out by choosing contouring factor as a basic parameter. In order to approach the problem theoretically, it is convenient to examine an equivalent single lateral weir in place of multiple weirs housed on the side of weir. It is reasonable to assume that the outflow through individual weirs of a system of multiple weirs will be equal when the water surface elevation in the canal is uniform along the reach that spans the weirs, when the weir parameter, F, is held constant. o The level of flow in the canal decreases continiously. This problem could be prevented (or decreased) by some geometrical variations. These are presented following, respectively. a - ) Contouring of the canal side b - ) Rise in the canal bed. To provide uniform water surface along the canal on the weir crest in case of side contouring and bed rising which depend on rates of discharge and amount of contouring two new dimensionless indicators R and R are mentioned. Q Q w w Q Q 1 _ 1 Rb = b ' Rh " IT 3 Q : Lateral weir discharge (m /s) w 3 Q : Main discharge in the canal (m /s) i b : Amount of side contouring (cm) B : Canal width (m) l z : Amount of bed rising (m) -xv- When the variable R has the value of unity, the D water surface profile will be horizontal in the canal reach spanning the weir, for case where side contouring is undertaken. Smilarly when the variable RHhas the value of unity, the water surface profile will be horizontal in the canal reach spanning the weir, for the case where side contouring is done. Because of this, variable is useful in the analysis of the experimental data. In this study, only contouring of the canal side condition was investigated because of time insufficiency. For experimental study of the problem a test canal was set up in the Hydraulic and Water Structures Laboratory at Istanbul Technical University. A 26 m. long, 98 cm. wide and 45 cm. high canal of the rectangular profile, which is already avalaible in the lab, was divided in two parts by use of reinforced concrete plates and 3 lateral weirs were placed at 335 cm. intervals. At the inlet, canal's width was adjusted to 30 cm. up to the first lateral weir, and, since the side wall of the test canal was built as to permit adjustment acording to desirable width, a gradual contouring was provided as from the first lateral weir up to the last one. The side weir is contructed as a sharp crested weir of variable size, the length and heigth of the weir is varried by the addition of fibre glass plates. The incoming water from the upper tank enters the initial part of the canal by gravity. In the mean time, the flow is calmed by various things such as perforated iron plates, submerged baffles and floating wooden plates. A 60° triangular ganging weir was used to determine the discharge of weired water from the lateral weir. Water height on the crest of weir which is required for discharge calculations was measured by use of limnimeter which was moved in the direction parallel and perpendicular to the canal axis so that water depth at the beginning of canals can be measured and changes on water surface through canal reach spans can be determined. After weired from lateral weirs, the remaining water in the main canal continues its journey and pours to the measurement bin at the downstream of canal. Quantity of poured water is defined by 90° triangular weir and water flows to lower bin. Test were held for three positions of side contouring and non-contouring position. -XVI - The side contouring positions are; 1 - l.st side contouring position (b=3, 3, 3) cm 2 - 2.nd side contouring position (b=l. 5, 4. 5, 7. 5) cm In each side contouring, sill height was altered for two times to be s = 15.00 cm, and s = 17.00 cm, and weir width was altered for three times to be L = 14 cm, L = 17 cm, L = 20 cm in each sill heigth. In addition all of these experiments were made with both control gates where at the end of canal opened and partly closed positions. During all tests, flow in the canal was kept constant in the subcritical regime (F < 1). In all the tests, Froude numbers at the in let were limited between 0.12 and 0.69. The outflow from lateral weir was changed between 14 lt/s and 75 lt/s. Test results are listed in tables and graphs. In the fourth chapter, the results of tests were evaluated and some suggestions were recomended. Water surface profiles which occur on weir reach spans as a result of contouring on the side of the canal are horizontal when dimensionless parameter R close to 1 and water surface profiles are less horizontal when dimensionless R is not close to 1. This condition can b be obviusly observed for 2.nd and 3.rd side contouring positions. When the sill height is increased, usually, flow speed at the inlet (V. ) increases, and outflow from lateral weir decreases. In the test results and graphs indicating the relation ship between theoretical discharge and test discharge it is observed that there is a harmony and a link between theoretical lateral weir discharge which was obtained by the use of hydrodynamic model, and that of lateral weirs in case of side contouring. While the control gates are open, the difference between the theoretical and real outflow from lateral weir increases because of downstream conditions. A favorable condition is taking enough quantity and each equal to another outflow from lateral weirs. From the point of wiev of outflow rates, more suitable results are observed at 2.nd and 3.rd side contouring positions when the outflow taken from 2.nd and 3.rd lateral weirs are compared to the outflow of l.st lateral weir. For outflow from lateral weirs: There is an avarage (3 - 4) % deviation on the 2.nd -XVII - lateral weir and 8 % deviation on the 3. rd- lateral weirs, when compared to the l.st lateral weir. This deviation reachs (18-20)% at the non-contouring position. The rates of outflow taken from lateral weirs acording to the quantity of water in main canal is presented in Table 4.3. The rates are very low, and water loss increases at the non-contouring position. On the other hand, water loss is very few at the 3.rd side of contouring position In practice, water distribution system with optimum side contouring ensures economic use of water. Moreover, due to side contouring, cross section of canal reduces, so the cost of canal reduces as well.