View source for Discharge diversions and returns

=Discharge diversions and returns=
02. Flow regulations
==General description==
Removal and downstream return of water from the river through a man-made
diversion structure called a ''bypass'' often results in significant flow reduction in the intervening section of the river’s course. This is a typical pressure that affects rivers used for hydropower, whereby flow is diverted from the river by a weir at higher altitude and conducted through a near horizontal bypass channel into turbines that are located downstream at a much lower altitude.
A similar pressure occurs in association with irrigation of farmlands located in the
floodplain and near the river margins, but in this case the return flows are greatly
reduced by plant water consumption, evaporation and infiltration, and may also suffer
from a reduction in water quality.
Diversion also takes place to supply urban areas and industries with water, and in these cases the return flow is affected by significant reductions in both water quality and quantity.
''Flood diversion'' is a special case of flow diversion and return that is designed to
alleviate flooding.

==Effect/Impact on (including literature citations)==

Although in temperate regions water abstractions may have relatively minor impacts, in Mediterranean countries they can represent major alterations with the potential to turn perennial rivers into intermittent rivers and to severely degrade physico-chemical conditions, if base flow becomes limited in relation to emissions or discharge of effluents (Prat & Munné, 2000; Menció ''et al''., 2010).
A review of low flow river conditions during dry periods of the year, as well as the
problem of changing minimum river flows as a consequence of climate variability is
presented by Smakhtin (2001).

==Case studies where this pressure is present==
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==Possible restoration, rehabilitation and mitigation measures==
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==Useful references==
Menció, A., Folch, A., Mas-Pla, J., 2010. Analyzing Hydrological Sustainability Through
Water Balance. Environmental Management 45: 1175–1190.

Prat, N., A. Munne, 2000. Water use and quality and stream flow in a Mediterranean
stream. Water Research 34: 3876–3881.

Smakhtin, V.U., 2001. Low flow hydrology: a review. Journal of Hydrology 240: 147–
186.

==Other relevant information==

[[Category:Pressures]][[Category:02. Flow regulations]]