Deltas Where running water flows into another body of water, its flow velocity decreases rapidly and it deposits sediments. As a result, a delta forms, causing the local shoreline to build out, or prograde. The simplest prograding deltas (ilerleyen deltas) exhibit a characteristic vertical sequence in which bottomset (alt takm) beds are successively overlain by foreset (n takm) beds and topset (st takm) beds. This sequence develops when a stream enters another body of water and the finest sediments are carried some distance beyond the streams mouth, where they settle from suspension and form bottomset beds. Nearer the streams mouth, foreset beds form as sand and silt are deposited in gently inclined layers. The topset beds consist of coarse-grained sediments deposited in a network of distributary channels (datc kanallar) traversing the top of the delta. Depending on the relative importance of stream, wave, and tidal processes geologists

Stream-dominated (akarsu egemen) deltas, consist of long fingerlike sand bodies, each deposited in a distributary channel that progrades far seaward. These deltas are commonly called birds foot (ku aya) deltas. In contrast, wave-dominated (dalga egemen) deltas the seaward margin of the delta consists of a series of barrier islands formed by reworking of sediments by waves, and the entire margin of the delta progrades seaward. Tide-dominated (gel-git egemen) deltas are continually modified into tidal sand bodies that are parallel to the direction of tidal flow.

Alluvial Fans (Alvyon yelpazeleri) An alluvial fan is a large, fanor cone-shaped pile of sediments that usually forms where a streams velocity decreases as it emerges from a narrow mountain canyon onto a flat plain. The sudden loss of velocity when a stream flows from steep mountains onto a plain causes the sediments to deposit on an alluvial fan. The loss of velocity is due to both the decrease in gradient and the widening or branching of the channel as it leaves the mountains.

Drainage Systems A drainage basin (akalama havzas) is an area from which a stream or river and its tributaries carry all surface runoff. High areas called divides (su blm izgisi) separate drainage basins from one another. Various arrangements of channels within an area are characterized as different types of drainage patterns (akalama dzenleri): Dendiritic drainage (dendritik akalama), consisting of a network of channels resembling tree branching, is the most common. It develops on gently sloping surfaces composed of materials that respond more or less homogeneously to erosion, such as areas underlain by nearly horizontal sedimentary rocks. Rectangular drainage (dikdrtgenimsi akalama) is characterized by right-angle bends and tributaries joining larger channels at right angles. Such regularity in channels is strongly controlled by geological structures, particularly regional joint systems that intersect at right angles.