View source for Loss of vertical connectivity

=Loss of vertical connectivity=
04. Morphological alterations
==General description==

Vertical fragmentation can be produced by physical processes that reduce river bed permeability such as siltation of the riverbed surface and clogging of pore spaces within stream bed gravels (Hancock 2002<ref>Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.</ref>). This may result from increased delivery of fine sediment to the river as a result of for example changes in land use or agricultural practices, as well from reduced flow energy, for example due to flow regulation. In either case, the balance between sediment supply and sediment transport is disrupted, leading to the accumulation of fine sediments within the river bed (Kondolf and Wilcock, 1996<ref>Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and evaluating objectives. Water Resources Research 32: 2589-2599.</ref>). In addition, physical modification of river channels, such as straightening and simplifying channel form (Kondolf ''et al''., 2006<ref>Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E. Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K. Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/</ref>) may reduce water depth and retention within the channel, adversely affecting vertical connectivity.

==Effect/Impact on (including literature citations)==
*HYMO (general and specified per HYMO element)
*physico - chemical parameters
*Biota (general and specified per Biological quality elements)
==Case studies where this pressure is present==
<Forecasterlink type="getProjectsForPressures" code="P20" />
==Possible restoration, rehabilitation and mitigation measures==
<Forecasterlink type="getMeasuresForPressures" code="P20" />
==Useful references==

Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.

==Other relevant information==

[[Category:Pressures]][[Category:04. Morphological alterations]]