Information and Advisory Note Number 18
February 1996
Rivers and their catchments: an overview
1.1 The relationship between a river and its catchment is one of the dominant themes of
hydrology and thus also in studies of river geomorphology and aquatic ecology. The range
of flows experienced, the timing of extreme floods and droughts, the nutrients and
sediments carried and the underlying terrain all reflect the strong interaction between a river
and its catchment This perspective underlies a series of Information and Advisory Notes
addressing the conservation of rivers and their catchments. Five of these Notes (18-22)
have been produced jointly by Scottish Natural Heritage and the Institute of Hydrology,
Scotland.
12. This particular note aims to provide a background to the other more specialised
Information and Advisory Notes, a general glossary of technical terms which will be
encountered in the Notes (particularly Notes 18-22), and a list of contacts and addresses.
1.3 The 'Rivers and their Catchments' series of notes, spanning the principal human
activities which impact on river form and processes, share a number of common themes,
and hence some overlap in their content. For example, times of flood are important in many
aspects of river behaviour: they are the few occasions in the year when erosion processes
effect rapid changes in the cross-sectional and plan forms of the river channel; at the same
time effective rainfall and runoff transport sediment from exposed areas of agricultural land,
flush out solutes which have been accumulating within soils or on forest canopies and, in
concentrated flow, can seriously erode forest roads or river banks with attendant
consequences for the subsequent deposition of sediment.
1.4 Timing emerges as a common theme; for example, the time of fertiliser application
relative to the next rainfall determines its impact on the quality of downstream
watercourses; the time of year in which forestry operations are earned out
influences the amount of sediment released into the river system; the timing of ditch
maintenance also affects the sediment impact on receiving waters.
1.5 Activities often associated with one particular type of land use may have parallels
elsewhere. For example, the use of buffer strips to protect streams from the excessive
fluxes of sediment and nutrients in pre-afforestation ploughing is also recommended as part
of good agricultural practice.
1.6 By focusing on the links between catchment and river, Integrated Catchment
Management (ICM) appears to be an increasingly attractive means to resolve potentially
conflicting activities. Operations which, taken alone, might be within the tolerance of a river
system become highly damaging in the presence of other pressures; multiple nutrient
sources and the algal blooms of Loch Leven provide a case in point ICM allows a river
system to be considered as a whole and for the resources of its catchment to be managed
sustainably and in harmony with the various demands of industrial water supply, fishery
management, effluent disposal and nature conservation. ICM can therefore be regarded as
comprising catchment management plans to which all the major interests in the catchment
subscribe. To be effective, such plans must be consistent with local authority development
plans and asset management plans of water supply utilities and vice versa.
1.7 Understanding river systems and their finks to wider catchment processes is a
fundamental aspect of integrated management This includes not only the underlying
controls of catchment hydrology, but also the geomorphology of river landforms and
processes, together with sediment and chemical fluxes and their associated pathways.
1.8 It is intended that the nature of river behaviour explained in these notes, and the impact
of various land management strategies, will encourage a greater awareness of river
systems per se, as well as the important role they play in providing habitats for many types
of flora and fauna.
Further Reading
Boon, P J, Holmes, NTH, Maitland, P S & Rowel, T A1994. A system for evaluating rivers
for conservation (TSERCON"): an outline of the underlying principles. Verhandlungen der
Internationalen Vereinigung fur theoretische und angewandte Limnologie, 25,1510-1514.
Maitland, P S, Boon, P J. & McLusky, D S1994. The Fresh Waters of Scotland: a National
Resource of International Significance. Chichester, John Wiley.
Werritty, A. 1995. Integrated Catchment Management a Review and Evaluation. Scottish
Natural Heritage Review No. 58.
Glossary of Technical Terms (for Information and Advisory Notes 18 -22)
Alluvial fan - deposit of sediment laid down by a stream or river where it emerges from the
confines of a valley or gorge into a basin. Lack of confinement allows horizontal expansion
of the flow, deceleration and deposition of some, or all, of the sediment load.
Ablation - the processes of ablation at a snow/ice surface include melting, evaporation,
wind erosion and removal of snow/ice by avalanching.
Attenuation - degree of reduction of peak discharge of a flood as it passes downstream.
Blanket forest - a commercial forest plantation, generally dense, large-scale and coniferous.
Braided channel - a network of shallow, interconnecting streams, typically in gravelly areas,
and characterised by frequent channel switching.
Brash - branch and leaf litter left on forest floor after harvesting operations.
Buffer zone/strip - a strip of land adjacent to a watercourse, offering protection from high
sediment and nutrient fluxes generated by forestry and agricultural activities. Sediment is
intended to settle out of suspension while the water carrying it may flow on into the stream;
nutrient buffering can occur as water seeps through the soil of the buffer strip.
Clearfelling - removing most or all of the existing stand of trees, thus producing an
environment for reproduction that is not influenced by the previous stand
Compensation water- the prescribed flow of water discharged into a stream below a
reservoir in order to provide for fisheries and conservation interests.
Culvert- covered channel or pipe which carries a watercourse beneath a road or other
structure.
Diffuse/non-point source - refers to supply of pollutant, sediment or nutrients from a wide
area, for example agricultural land, as opposed to a point source such as a stream or
sewage outfall.
Discharge - the amount and rate of flow, normally expressed as cubic metres (cumecs), or
litres, per second.
Esker- ridge, often sinuous, resulting from the deposition of sand and gravel by a subglacial stream.
Eutrophication * nutrient enrichment of river waters, often as a result of enhanced inputs
from agricultural activities, industrial or sewage effluents.
Flashy river- a river which responds very quickly to rainfall, the flow of water rising rapidly to
a high peak before receding similarly. Typical of small, steep, upland catchments.
Floodplain - flat, valley-bottom area of sediments deposited in floods, and typically being
reworked as the course of a river repeatedly shifts across the valley floor.
Fluvial - describing processes and landforms of the river system.
Forest cycle - the rotation of forest planting, growth and felling. Ground preparation may be
included in the planting stage.
Freshet- artificial flood on impounded rivers, released for fisheries interests.
Gabion -wire cage filled with rocks, used to protect banks from erosion or to deflect the
current
Groyne - structure protruding out into a channel to deflect the current
Gully- a larger, more permanent channel than a rill.
Hydrogeology- the study of the geological factors relating to the earth's water, including its
occurrence, distribution and movement
Hydrology - the study of all waters in and upon the earth, including underground water,
surface water and rainfall.
Interception - rainfall caught on leaf/branch surfaces of vegetation, subsequently lost back
to the atmosphere by evaporation.
Interstitial spaces - spaces between substrate particles.
Meander- bend in a river, formed by natural channel processes.
Moraines - landforms resulting from material deposited by a glacier.
Mounding - a relatively shallow scoop of surface material turned over to create a bare patch
of ground for tree planting.
Photosynthesis - production, in green plants, of organic compounds from carbon dioxide
and water using light energy from the sun.
Point bar- area of fine sediment, accumulating by fluvial deposition, on the inside of a bend,
and typically balanced by erosion on the opposite bank.
Pool- Portion of the stream with lower velocities and deeper water than surrounding areas.
Used by fish for resting and cover.
Primary productivity - synthesis of organic matter from inorganic materials, usually by
photosynthetic green plants.
Redd- area of streambed dug out by the female salmonid, before spawning, where she lays
her eggs.
Riffle - shallow rapids where water flows swiftly; food supply of fish, i.e. invertebrates,
concentrate here. Female salmonids dig their redds in riffle areas.
Rill- small channel that can develop during a runoff event, particularly on unvegetated
slopes.
Riparian - situated on the banks of a river or stream.
Ripping - disruption of subsoil, using a blade, to allow planting.
Scarifying - (also screefing) scraping away the surface vegetation prior to planting to
prevent weed competition.
Scavenging - enhanced interception of rainfall and particulate pollutants by an
aerodynamically rough surface, especially the canopy of a mature forest
Sediment starvation - condition arising immediately downstream of a reservoir where,
because of deposition in the reservoir, the river carries much less suspended load or bed
load than expected in high flows. Enhanced erosion results.
Siltation - deposition of fine sediment by a river or stream.
Snowmelt flood - flood generated by melting of large volumes of snow.
Sublimation - direct loss of snow to water vapour as a result of solar energy; no
intermediate melting stage.
Substrate - mineral and/or organic material that forms the bed of a stream. Includes clays,
silts, sands, gravels, cobbles, boulders and bedrock.
Suspended Sediment portion of the sediment load of a river that moves in suspension.
Thalweg - line connecting deepest points along a streambed.
Thermal stratification - layering of water according to its temperature, and hence density.
Transpiration - stomatal water loss from a plant or tree.
Trophic level - division of a food chain defined by the method of obtaining food.
Turbidity - amount of fight scattered or absorbed by a fluid as a result of its content of
suspended particles and dissolved load.
Useful Addresses
Scottish Natural Heritage
Research and Advisory Services Directorate
2 Anderson Place
Edinburgh
EH6 5NP
Tel: 0131-447 4784
Aquatic Environments Branch {provides information on biota in the aquatic
environment): Tel. 0131-447 4784
Earth Sciences Branch {provides information on the physical processes in the aquatic
environment): Tel: 0131-446 2451
Scottish Natural Heritage
Policy Directorate
12 Hope Terrace
Edinburgh
EH9 2AS
{Provides information on wide range of policy, strategy and legislation issues):
Tel: 0131-447 4784
Institute of Hydrology
Alpha Centre
Innovation Park
Stilling
FK9 4NF
(Involved in a wide range of research and monitoring relating to water in the environment)
Tel: 01786 447612
The Scottish Office Agriculture, Environment and
Fisheries Department
Engineering, Water and Waste Directorate
Victoria Quay, Leith
Edinburgh
EH6 6QQ
(Responsible for water management within SOAEFD)
Tel: 0131-6568400
Farming and Wildlife Advisory Group
National Agricultural Centre
Stoneleigh
Kenilworth
Warwickshire
CV8 2RX
(Provides advice on agricultural and wildlife management; local Farm Conservation
Advisers are based in Ayr, Cupar, Dumfries, Forfar,
Inverness, Inverurie, Kirkwall, Lanark, Lerwick, Newbridge, Oban, Paisley, Perth, St
Boswells and Stirling)
Tel: 01203 696760
Forestry Authority/Forest Enterprise Scotland
231 Corstorphine Road
Edinburgh
EH127AT
(Forestry Authority, the regulatory arm of the Forestry Commission, providing advice to the
public on forest management).
Tel. 0131-334 0303
(Forest Enterprise: responsible for managing Forestry Commission owned forests, including
timber harvesting and recreation)
(Conservancy Offices are located in Lockerbie, Galashiels, Huntly, Perth, Dingwall and
Glasgow)
Scottish Environment Protection Agency
Head Office
Erskine Court
The Castle Business Centre
Stirling
FK94TR
(Provides advice on a wide range of water related issues and is responsible for issuing of
consents to discharge substances into the aquatic environment)
Tel: 01786 457700
Regional Offices are located at:
North Region HQ
Graesser House
Fodderty Way
Dingwall
IV149XB
Tel: 01349 862021
West Region HQ Rivers House Murray Road East Kilbride G75 0LA Tel: 01355238181
East Region HQ
Clearwater House
Heriot-Watt Research Park
Avenue North
Riccarton
Edinburgh
EH144AP
Tel: 0131-449 7296
Authors
Institute of Hydrology, Stirling.
Jonathan Clark, Earth Sciences Branch, Scottish
Natural Heritage