Plajlar ince kumlardan iri kayalara kadar değişen büyüklükte kayaların birikmesiyle oluşmuş jeolo-jik bölgelerdir. Plajlar kara, hava ve deniz birleşiminde yer almakta olup morfolojileri dalga meka-niği, katı madde özellikleri ve mekaniği, plaj yeraltı suyu akımı ve mekaniği ile rüzgar etkilerinin etkileşimine bağlıdır. Sahil drenajı, sahil altına yerleştirilen perfore drenaj boruları vasıtasıyla dalga ve yeraltı sularının drene edilmesi ve böylece yeraltı su seviyesinin düşürülmesi ile sızma oranının arttırılması prensibine dayanır. Araştırmada ince taneli kuma sahip sahillerde sızma ora-nının arttırılması ile erozyonun nasıl değişeceği deneysel olarak incelenmiştir. Çalışmanın amacı değişik dalga özelliklerinin etkisinde drenaj borusunun farklı konumlarında profil şeklinin ve dre-naj debisinin tayin edilmesidir. Bu amaçla fiziksel bir model geliştirilmiş ve basit analitik çözümler önerilmiştir. Bu çalışmalar daha sonra düzenli dalga koşullarında yapılan laboratuvar çalışmaları ile karşılaştırılmıştır. Drenaj debisinin tahmini, inşaa edilecek su toplama kuyusunun hesabında ve bu kuyudan suları denize deşarj edecek pompa kapasitesinin tayininde kullanılmaktadır. Öte yan-dan, değişik dalga ve drenaj borusu yerleşim yerleri için erozyon alanının tahmin edilmesi, kıyı du-varları ve kıyı kaplamaları gibi çeşitli yapıların stabilitelerinin belirlenmesi açısından önemlidir. Bu çalışmada hem drenaj debisi hem de erozyon alanı parametrelerinin tahmini için denklemler önerilmiştir. Sahil drenajı ile erozyon alanında azalma yaşanmıştır. Bunun nedeni olarak yer altı su seviyesinin düşmesi ile sızma oranında artma ve buna mukabil katı madde efektif ağırlığında artış söylenebilir. Profil verileri incelendiğinde erozyon alanındaki artışın en önemli nedeni ise dalga tırmanma yüksekliğinde yaşanan azalma görülmüştür.

Beaches play important roles in both the dissipation of wave energy and for the recreational purposes. They are generally in dynamic equilibrium. But, due to increasing industrial activities and population, human interference into the beaches occurs and the dynamic equilibrium deteriorates. In order to control the cross-shore and alongshore sediment transport in eroding beaches, some struc-tures like breakwaters, groins, seawalls are con-structed. These structures are composed of massive concrete blocks which lead to loss in aesthetic vi-sion. Moreover, these structures are very difficult to relocate after construction. Beach drainage is an erosion control method studied in-situ, laboratory and numerically and offers an alternative to massive coastal control structures. Main philosophy lying under this method is lowering the water table and increasing the infiltration through the sediment matrix. As the infiltration rate increases, the probability of liquefaction and effec-tive weight reduction of sediments will be reduced. Also, water that infiltrates during the wave runup will lead to reduction in flow velocity during both in runup and run-down phases. This reduction in flow velocity will lead to reduction in shear stresses. Recently, some numerical studies claim that for fine sediments, in case of infiltration, erosion occurs due to offshore migration of sediments. On the other hand, reports of in-situ investigations reveal that, in case of infiltration either the beach accretes or the erosion is reduced. Experiments are conducted in a narrow flume with 22m in length, 1m in width and 80cm in depth. Slope of beach profile is always kept constant (1:5), the profile and drainage flow rate data are measured. The median grain size of the sediment is d50=0.3 mm. The diameter of the drainage pipe is 50mm and is laid all width of the flume. The pipe is perforated in 8mm holes to allow the water suction. Geotextile sheet is wrapped over the pipe to prevent the holes from sediment clogging. 6 drainage pipe locations are determined; beach profiles and drainage flow rates are measured in these locations. Between the beach head and the ground water trench, geotextile filter layer is placed to prevent clogging of the holes, which allow the ground water flow through the beach. Ground water level is al-ways kept constant in all experiments as the same as the still water level. According to the experimental analysis, the waves which have lower height than 5.5 cm do not result in erosion in the profile in no-drain case. The area of the erosion is almost linearly increasing with wave height. In case of drainage, the wave height which does not result in erosion in the profile is observed as 8cm. Center of gravity of the offshore bar mi-grates landwards as the drainage pipe location ap-proaches the intersection of beach profile and still water line. There is no direct relation between the drainage flow rate and erosion area. The important factor is that whether the runup/rundown wave water or the existing ground water is drained. The ground water is drained as the pipe location migrates landwards. According to the experimental analysis results, the most obvious reduction in the erosion area is ob-served when the pipe is placed in location (2). When the data measured in location (2) is compared with no-drain data, erosion area reduction rate is reduced when the wave height is increased. When the wave height is increased up to 25 cm, drainage has no advantage to reduce erosion Dimensionless drainage flow rate and dimensionless erosion area parameters are derived analytically by using the data measured in pipe locations of 1, 3, 4 and 5. Derived equations are verified by using loca-tions 2 and 6. The increase in the infiltration rate by lowering the water table leads to reduction in the effective weight of the sediments and decrease in the flow velocity of the runup/rundown swash flows. When the profile graphs are investigated, the main reason for the ero-sion reduction should be the reduction of the wave runup height. Increase in the infiltration rate leads to reduction of the wave runup wave flow velocity and quantity, resulting in the decrease of runup limit of water waves. In the down-rush phase, the flow velocity is also reduced and the ability to carry sed-iments is decreased.