Editing Entrenched river (section)

== Causes ==
As observed above, an entrenched river can be caused by either tectonic uplift in the area or when the lowering of the sea level occurs. It can also be caused by increased level of downcutting or a collapse of [[moraine]]-dammed lake downstream, or capture of the river by another river. Moreover, the process of river rejuvenation can also be the cause of river entrenchment, especially when the process has occurred due to tectonic uplift. River rejuvenation increases the power of the flowing water and, therefore, the process of erosion is accelerated.

Studies show that [[tectonic movement]], particularly movement associated with uplift, can influence spatial patterns of [[erosion]] and [[sedimentation]]. Although it is very difficult to offer detailed information of past [[tectonic]] activity, the basic temporal and spatial scale can show evidence of how this movement leads to the formation of an entrenched river.<ref>Shields Jr, F. Douglas, Andrew Simon, and Lyle J. Steffen. "Reservoir effects on downstream river channel migration." Environmental Conservation 27.01 (2000): 54-66.</ref> Various authors have used an entrenched river as evidence of tectonic movement in the past, and in this way they have proven the significant role of tectonic uplifts in the formation of an entrenched river.<ref>Goldberg, Paul, Vance Holliday T.,  and Reid Ferring C.  Earth Sciences and Archaeology. Boston, MA: Springer US, 2001. Print.</ref>

Several studies have cited incised meander a major feature of river entrenchment, as an impact of river rejuvenation. On the other hand, scholars argue that incised meanders and entrenched meanders are features formed before river rejuvenation. Incised meanders occur at the base of the river and they occur when the river base level has reduced, thus giving the river enough power for vertical erosion to take place. Some studies also indicate that [[Human impact on the environment|anthropogenic]] factors such as clearing of vegetation, development of dams, and [[reservoir]] and [[urbanization]] are also causes of river entrenchment. For example, [[gravel]] mining along the [[Russian River (California)|Russian River]] developed the Middle Reach pit, which in turn led to the creation of the entrenched river. According to Posamentier, in the 1950s and 1980s, the Russian River had [[gravel]] pits and dry [[creek (stream)|creek]]. However, over time the river has become entrenched due to [[mining]] (p.&nbsp;1777).<ref>Posamentier, Henry W. "Lowstand alluvial bypass systems: incised vs. unincised." AAPG bulletin 85.10 (2001): 1771-1793.</ref>

Urbanization and clearing of vegetation increase runoff water, which in turn increases water volume, especially during rainy seasons. Therefore, the increased level of vertical erosion of the river increases the power of the water, leading to erosion of the river. A study of [[San Pedro River (Arizona)|San Pedro River]] and another river in the southwest have indicated that floods were the main cause of river entrenchment in the 18th century. The study shows that increased population and human activities in these places increased floods and, consequently, the volume of runoff water (Hereford 43).<ref>Hereford, Richard. Entrenchment and Widening of the Upper San Pedro River, Arizona. Boulder, Colo, 2003. Print.</ref>