Water resources: hydrological conditions
Standards have been developed for water flow conditions in rivers and in lochs, matched to biology.
Water resources standards proposed in this paper |
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Standard | Rivers | Lochs |
Water flow | % change from natural flow | % change from natural inflow |
Proposed numerical standards for flow conditions in both rivers and lochs vary with water body 'type', as discussed earlier. The typology used to classify rivers and lochs for water resources are defined in the next sections, followed by the numerical standards that are proposed in each case.
Rivers - water resources
1. River typologies for water resources
Overall: for water quality, rivers are divided into types depending on the underlying geology, catchment gradient and altitude:
Table A15: River typology - for water resource standards |
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Type | Gradient (m/km) | Altitude (m) | Description |
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A | Clay and/or chalk; low altitude; low slope | A1 | 0.8 ± 0.4 | 36 ± 25 | Predominantly clay. SE England, E Anglia, Cheshire plain |
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Eutrophic †; silt-gravel bed | A2* | Slightly steeper 1.7 ± 0.8 | Low altitude 55 ± 38 | Chalk catchments; predominantly gravel beds; base-rich |
B | Hard limestone and sandstone; low-medium altitude; low-medium slope; typically mesotrophic † with gravel-boulder or pebble-cobble bed | B1 | 4.1 ± 9.9 | 93 ± 69 | Hard sandstone, calcareous shales. Predominantly S and SW England and SW Wales |
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B2 | Shallower than B1 2.7 ± 10.7 | 71 ± 58 | Predominantly NW and E Scotland |
C | Non-calcareous shales, hard limestone and sandstone; medium altitude; medium slope; oligo-mesotrophic † with pebble, cobble and/or boulder bed | C1 | 5.4 ± 6.5 | 101 ± 84 | Hard limestone; more silt and sand than C2; mesotrophic † |
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C2 | Steeper than C1 7.3 ± 10.8 | 130 ± 90 | Non-calcareous shales; pebble bedrock; oligo-mesotrophic † |
D | Granites and other hard rocks; low and high altitudes; gentle to steep slopes; ultra oligotrophic † | D1 | Medium gradient 11.3 ± 15.6 | 93 ± 92 | Oligotrophic †, substrate finer than D2 (including silt and sand); more slow flow areas than D2 |
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Oligotrophic † with cobble, boulder, bedrock and/or pebble bed | D2 | High gradient 25.5 ± 33 | High altitude 178 ± 131 | Stream order 1 and 2 bedrock and boulder; ultra-oligotrophic †; torrential |
* Split into A2 (headwaters) and A2 (downstream) to reflect different sensitivities of chalk rivers. |
† These terms are all measures of the biological productivity of the water. Oligotrophic waters are unproductive ; eutrophic waters are highly productive ; mesotrophic waters lie in between. |
This typology is based on some existing classifications. It is similar to that used by the Environment Agency in England and Wales, as part of their Resource Assessment and Management ( RAM) Framework. Some river types have been grouped together, where it was thought to be difficult to reliably distinguish them on the basis of summarising high level catchment data.
2. Water flow standards - percent change from natural conditions
Table A16: Water flow (% permitted change from natural flow) - rivers |
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'High' Status |
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River type | Season | Flow decreasing ? |
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Flow > QN95 | Flow < QN95 |
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ALL | ALL | Up to 10 | Up to 5 |
'Good' Status |
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River type | Season | Flow decreasing ? |
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Flow > QN60 | Flow > QN75 | Flow > QN95 | Flow < QN95 |
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A1 | Summer: Apr-Oct | 30 | 25 | 20 | 15 |
Winter: Nov-Mar | 35 | 30 | 25 | 20 |
A2 (downstream), B1, B2, C1, D1 | Summer: Apr-Oct | 25 | 20 | 15 | 10 |
Winter: Nov-Mar | 30 | 25 | 20 | 15 |
A2 (headwaters), C2, D2 | Summer: Apr-Oct | 20 | 15 | 10 | 7.5 |
Winter: Nov-Mar | 25 | 20 | 15 | 10 |
Salmonid spawning and nursery areas (not chalk rivers) | Summer: Apr-Oct | 25 | 20 | 15 | 10 |
Winter: Nov-Mar | 20 | 15 | Flow > QN80 10 | Flow < QN80 7.5 |
In cases where flow is artificially increased, e.g. by transferral of water between water bodies, or discharge of treated water to a watercourse, the proposed standards should be applied to changes in the actual flow, not the original flow. |
'Hands-off' restrictions
UKTAG also recommends 'hands-off' restrictions to protect extremely low flows, where the natural flow is at or below QN98 levels. UKTAG recommends that, for these low flows, if the total actual flow is less than four times the maximum removal volume permitted by the proposed standard, no abstraction would be permitted. (This means no abstraction would be permitted for QN98 or smaller flows where the maximum reduction in flow allowed by the proposed standard - e.g. 15% from natural flow in an A1 river, see Table A16 above - is over 25% of the total flow.)
As discussed in section C, the need to consider such restrictions in Scotland will be very rare. For the vast majority of river water bodies in Scotland, if the volume being abstracted meets the proposed standard for flows less than QN95, it will also be less than 25 % of the QN98 volume. The few water bodies where this is not the case are steep, spate rivers which rise and fall rapidly in response to rainfall.
Lochs - water resources
1. Lochs typologies for water resources
Overall: For water resources, lochs have been classified according to six different parameters:
Table A17: Lochs typology for water resources |
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Tier | Units | Categories |
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Geology | As UK lakes typology ( UKTAG 2003) | Peat | Low Alkalinity | Moderate Alkalinity | High Alkalinity | Marl | Brackish |
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Mean depth | (m) | Very shallow (Sh)
< 3 | Deep (D)
 3 |
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Altitude | (m) | Lowland
< 200 | Mid-altitude
200 to 800 | High-altitude
800 |
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Size (loch area) | (ha) | VS/S
1 to 50 | L/VL
50 |
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Season | | Summer
Feb - Sept | Winter
Oct - Jan |
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Basin form* | V d = 3D mean/D max | Vex (VCx/Vx)
< 0.67 | Lin (Scx/L/C)
0.67 |
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* For further information on these typologies and calculations, see UKTAG papers at www.wfduk.org. |
2. Water inflow standards - percent allowable deviation from natural net inflow
Comparison
The standards that have been used to characterise lochs and assess risks from abstraction under the WFD allow between 15 and 25% of the natural inflow to be abstracted, depending on the level of flow (see below). Reports of the characterisation carried out in 2004 can be obtained from the SEPA website: www.sepa.org.uk/publications/wfd/index.htm.
Table A19: Inflow characterisation standards (% reduction of natural inflow) - lochs |
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Sensitivity to flow | Flow decreasing ? |
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At QN50 | At QN70 | At QN95 |
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All categories | 25 | 20 | 15 |