CHAPTER 14
Fluvial Systems: catchments and rivers
Introduction
Flowing water links the terrestrial sector of the global hydrological cycle with continental denudation, of which it is a prime agent, and later stages of geological fractionation.
Tectonic uplift empowers fluvial erosion, on contact with water cycled by solar energy and
concentrated in surface channels by catchment processes. Progressive sediment transfers
occur between upper and lower catchments, and subsquently between lower catchments
and marine basins. This is a continuous process in ‘short’ systems where coarse, raw fluvial
sediments are swept as molasse into trenches and back-arc basins close to orogens. Flood
plains form more enduring sediment stores in ‘long’ systems, where reworking continues
mechanical and chemical sorting before onward transfer of mature sediments to marine
basins.
The chapter commences with the recognition of the drainage basin as the fundamental
fluvial landsystem. Its identifiable hydrogeological characteristics convert measurable
hydrometeorological inputs to stream flow through a series of in-line stores and transfer
processes. The hydrograph is valued as an aid in summarizing discharge characteristics and
components. Stream flow is shown to represent an inevitable and more efficient means of
moving water at the surface than overland flows. The concept of efficiency is central to all
subsequent fluvial geomorphic processes. Sea level provides the principal base to which
rivers work, and their long profile corresponds to a power curve, with exponential energy
decay reflecting increasing age and lowering of, or distance from, source orogens.
Coalescence of tributary flows steadily increases the volumes of water and sediment which
trunk rivers are required to move but also provides a corresponding energy saving as
proportionally less water makes friction contact with the channel. Water movement in channels is outlined prior to establishing core relationships between water and sediment
discharge, channel geometry and stream velocity. Channel geomorphic activity is shown to
represent a continuous attempt to balance these parameters, prior to placing them in
context in catchment-scale fluvial landsystems.
Chapter Summary
Generation of channel flow
•
The catchment, or drainage basin, is a landsurface unit which generates stream flow
in a principal stream or trunk river. It forms a single accounting unit for the
calculation of water and sediment balances.
•
Catchment surface and subsurface components convert water, snow, ice and
influent groundwater inputs into river discharge, evapotranspiration and effluent
groundwater outputs.
•
The three-dimensional landsystem is bounded by a watershed and is modelled as a
series of in-line stores and transfer routes which delay the generation of stream
flow. This moderates the episodic nature of inputs and generally sustains stream
flow during dry spells.
1
•
Hydrometeorological transfers between the atmosphere and catchment are
measured in terms of precipitation amount, type, frequency, intensity and duration;
they strongly influence the
rate and timing of onward transfers.
•
Evapotranspiration returns a proportion of the water-equivalent inputs to the
atmosphere, although for a significant component this occurs after water enters the
drainage network.
•
Hydrogeological transfers occur by gravity draw-down through each store as
storage capacity is reached. Above-ground transfer is influenced by vegetation
characteristics and subsurface transfer by the hydraulic conductivity of soil and
rock.
•
Stream gauging measures discharge over time and permits the construction of
hydrographs which summarize the nature of its response to precipitation events
and the components of stream flow.
Stream flow in channels
•
•
•
•
•
•
•
•
Overland flow, which occurs when precipitation intensity exceeds infiltration rates,
is unstable and inefficient, and surface irregularities concentrate water in parts of
the sheetflow.
Horton overland flow on non-vegetated surfaces is distinguished from saturated
overland flow, which emerges through soil towards valley floors.
Channel initiation occurs where the erodibility of the landsurface and erosivity of
the flow permit and commences as ephemeral rills or more enduring gullies.
Hydraulic efficiency increases immediately, with less water in frictional contact with
the surface, and remains a priority for stream flow in view of downstream potential
energy decay.
Stream flow encounters frictional resistance with the channel, solid sediment load,
atmosphere and internally between ribbons of water as laminar or turbulent flow
conditions develop, depending on water depth and channel roughness.
Channel geometry describes the wetted perimeter and hydraulic radius of any stage
of flow in a small channel segment of known length and slope and, with stream
velocity, is used to calculate discharge.
Channels are dynamic and their geomorphic activity and landforms are the
response to constant changes in their power threshold, form and function.
The drainage network is the sum of stream segments throughout a catchment,
responsible for transferring incremental amounts of water and sediment
downstream through a stream hierarchy and pattern which reflect catchment
attributes and stage of development.
Channel erosion and sediment transfer
•
Stream power leads to channel erosion through the removal of soluble minerals,
corrasion by entrained particles and fluid shear stress directed at the channel
boundary by turbulent flow.
2
•
Fluid stressing, capable of eroding soft and well fractured rocks, is enhanced by
cavitation caused by the implosion of bubbles against the channel boundary during
rapid turbulent flow.
•
Subaqueous erosion is augmented by bank caving above the water surface at low
flow stages, through the removal of lateral support.
•
Eroded debris and material delivered to the stream from adjacent slopes are
entrained when stream velocity exceeds the entraining velocity for a given particle
size, summarized in Hjülstrom’s diagram.
•
Downstream sediment transfer occurs as suspended, bed and dissolved loads.
•
Deposition occurs when stream competence falls below the critical velocity
required to maintain movement.
•
The variety of transport styles and particle sensitivity to competence lead to a
considerable amount of particle sorting by size, which is reflected in fluvial
sediments.
Fluvial landsystems
•
The drainage basin landsystem is characterized by upper, erosion-dominated, and
lower, deposition-dominated, components, with typically concave river longprofiles reflecting the downstream decay of potential energy.
•
Bedrock channels are therefore more common in uplands where rivers incise steepsided narrow valleys, or gorges, in areas of active (orogenic) or renewed uplift
(rejuvenation).
•
Upland fluvial sediments may be restricted to discontinuous pockets of raw, coarser
sands and gravels with debris cones or alluvial fans where tributaries join less steep
channels.
•
Alluvial channels are more common in lowlands where silt–sand–gravel beds are
spread over flood plains by meandering rivers and overbank floods.
•
Straight channels are rare, occurring only when bed load is low, and meandering
develops as channel geometry responds to changes in water and sediment
discharge. It consumes surplus energy by lateral erosion and the larger wetted
perimeter implicit in sinuosity.
•
Meanders develop in close association with a riffle–pool sequence of bedforms of
alternating deposition (riffle) releasing energy for erosion (pool), leading to
increased sediment load, etc.
•
Where streams divide at low flow around multiple bars or riffles and dissect them
at high flow the channel becomes braided, or is said to be anabranching if stabilized
by vegetation.
•
Meandering, braiding and anabranching characterize the floodplain landsystem and
rework its extensive fluvial sediment spreads. The enduring nature of the flood
plain is also marked by aggradation or incision and terrace formation in response to
changing sea level, climate and land use.
3
CASE STUDY : Aspects of the River Severn Catchment, Wales and England
Aims and Objectives Catchment studies are one of the most prominent areas of
applied geographical and environmental studies, integrating the specific threedimensional landsystem unit of a drainage basin with its human occupancy and land
use. Catchment climate determines the hydrometeorological inputs whilst the basin
landsystem components (soils, geology, slope and ecosystems together with human
structures and activities) determine the hydrogeological volume, routeing and timescale
of water transfers. Watershed models, calculation of the water balance and
measurement of the hydrographic character are all necessary ingredients in the human
management of the catchment This case study identifies the principal catchment
characteristics of Britain’s biggest river ~ the Severn ~ and directs the reader to
website resources of recent, current and continuing time-and-space data which create
good opportunities for interactive analysis of its catchment hydrology and problematic
management.
Catchment character
The River Catchment is Britain’s largest river in every sense. The trunk river is 347 km
in length from the source on Plynlimon Fawr (756m OD) in the Cambrian Mountains,
mid-Wales to the commencement of its tidal estuary ~ near the Haw Bridge gauging
station between Tewkesbury and Gloucester in western England (Catchment Map
available through the Centre for Ecology & Hydrology and National River Flow
Archive listed under Web Resources below) Its catchment above Haw Bridge covers
9,895 km2 but at its maximum extent ~ including the Leadon (right-bank tributary) and
Chelt (left-bank) below that ~ the overall catchment exceeds 11,000 km2. The highest
point on its watershed is 827m OD on Cader Berwyn in the extreme north-west, and
mean discharge as it enters the tidal stretch is 104.95 m3 sec-1. For comparison, the
equivalent data for the River Thames is that its catchment extends over 9950 km2 above
its tidal limit at Teddington Lock, Richmond-upon-Thames, flows for 345 km below a
maximum watershed altitude of 330m OD in the Cotswold Hills, Gloucestershire and its
mean discharge at Teddington is 65.59 m3 sec-1.
The catchment and river possess two quite distinct characters either side of the WalesEngland border. The Hafren, its Welsh name, rises on the east side of the Cambrian
mountains within a few hundred metres of the source of the River Wye, also one of
Britain longest rivers and which joins the estuarine Severn at Chepstow in south-east
Wales. Although arising from the same upland moorland watershed, on Lower
Palaeozoic rocks of low permeability, the Rheidol and Ystwyth reach the Irish Sea
within 40 km to the west ~ little more than 10% of the distance the Severn travels and
hence with a much steeper profile and faster mean flow. Nevertheless, the Severn and
its upstream tributaries also have steep profiles, rapid mean flow and “flashy”
hydrographs as a result of the high elevation of the Cambrian Mountains plateaux
(Plates 1 and 2), high orographic mean precipitation of 2482 mm yr-1 at the Plynlimon
gauging station (Plate 3) and generally 1700-2000 mm yr-1 in the mountains (Figure 1).
The Severn is joined by one major left-bank tributary, the Vyrnwy, before it crosses the
English Border downstream of Welshpool and ~ simultaneously ~ passes below the
4
generalized 200 m OD contour and onto permeable Mesozoic (Triassic) sandstones of
the Cheshire-Shropshire Plain.
Plate 1 A typical landscape on the Cambrian Mountains’ summit plateau near Plynlimon Fawr, with thin
soils and quite intensively grazed moorland vegetation shedding high rainfall quickly. (Photo: Ken
Addison)
Plate 2 Off the eastern plateau edge, slopes become much steeper in narrow tributary valleys and shorten
lag times to the rivers.(Photo: Ken Addison)
5
Plate 4 Flume for stream gauging in a steep catchment on Plynlimon, mid-Wales. Its height, and baffles
to dissipate stream energy, reflect the ‘flashy’ nature of upland stream flow. Photo: M.A. Fullen.
Figure 1 Abstract from Average annual total precipitation amount (mm) for 1971-2000, currently Figure
2:42 on page 68 of Jenkins, G.J, Perry, M.C. and Prior, M.J.O (2007) The climate of the United Kingdom
and recent trends, UK Climate Impacts Programme, Exeter: Met Office Hadley Centre (Exeter EX1 3PB)
ISBN 978-906360-01-6 enquiries@ukcip.org.uk © Met Office. taken from: UK CI08: The Climate of the
UK and recent trends.
6
Thereafter, the Severn undergoes two abrupt changes in direction which are probably
attributable to significant Neogene developments of the British Landform and
superimposed river systems, and certainly to their Quaternary ~ probably Late
Pleistocene ~ disruption by glaciers. As it crosses the border, the Severn turns almost
90o east ~ away from its NNE line which would take it into the River Dee just 20 km
north at Overton; the Dee itself also swings abruptly northwards from its easterly course
out of Wales. The Severn swings again 40 km further east, by 60o to flow south towards
the Gloucester and the Severn Estuary ~ this time diverted by the Ironbridge Gorge
from a line which would have taken it into the River Trent 40 km away near Stafford
(Plate 14.4).
Plate 4 The world’s first Ironbridge, completed in 1779, spanning the Severn in Ironbridge Gorge. The
high arch is a functional element of the bridge, designed to allow Severn sailing barges carrying industrial
raw materials and good to pass underneath at most stages (depths) of the river, which can rise quickly
through the gorge. (Photo: Ken Addison)
The entire region occupied in common by stretches of the Dee, Severn and Trent was
breached by ice passing from the Irish Sea basin between the Cambrian Mountains to
the west and Pennines to the east. A combination of glacial erosion on the flanks of the
uplands, extensive lowland glacial deposition in the Plain ~ including the WrexhamEllesmere-Wolverhampton moraine and esker complexes, and subglacial meltwater
erosion of Ironbridge Gorge radically reorganised Borderland drainage systems. The
presence of an essentially-Devensian (< 125,000 ka) series of river terraces below
Bridgnorth helps to confirm the Late Pleistocene age of these events. In all likelihood,
the Severn and Dee were tributaries of an older “super-Trent” system draining
eastwards out of the Welsh Mountains into the North Sea; now they both outflow
westwards into the Irish Sea basin, after turning almost 180o.
The Middle and Lower Severn meanders in its floodplains across two substantial
topographic basins on permeable rocks, generally sandstones and mostly of Mesozoic
age. Floodplain elevations everywhere are < 50 m OD downstream of Shrewsbury
(mean flow c. 43 m3 sec-1) and in the rainshadow of the Cambrian Mountains with <
750 mm yr-1. The upper floodplain is centred around Shrewsbury and collects the major
7
tributaries of the Rea (right-bank), Perry, Roden and Tern (left-bank) which raise the
mean flow to 60 m3 sec-1 in just 15 km as the river enters the Ironbridge Gorge. Exiting
the gorge 30 km to the south at Bewdley with a mean flow just 1.5 m3 sec-1 higher, the
river now enters the Worcester-Tewkesbury-Gloucester floodplain. Two major
tributaries ~ the Avon (left-bank) draining the south-west Midland Plain and the Teme
(right-bank), whose catchment sweeps in a long, concentric arc south of the Severn
itself and also rises in Wales ~ contribute mean flows of 16.7 and 17.5 m3 sec-1
respectively, adding almost 60% to overall mean flow in just 30 km between Worcester
and Gloucester.
The hydrography, and therefore management, of the Severn is complex, the more so
through the abrupt switch along the eastern scarp of the Cambrian Mountains from an
essentially-upland to meandering flood-plain river. In Wales, it drains steep-sided
valleys in high-rainfall, winter maxima conditions on -permeability strata through an
almost entirely moorland, pastoral and occasionally forested catchment. It carries the
water and sediment discharges associated with this, in “flashy” hydrographic style into
England. Here, additional discharge is suppressed and regulated by much lower rainfall,
with increasing tendencies towards summer and autumn maxima (particularly from the
Avon sub-catchment), permeable strata and a more arable farming catchment. There are
no major conurbations and relatively few large towns and industrial areas to seriously
disturb catchment characteristics but the floodplains provide major river and
groundwater abstraction sources for public water consumption well beyond the basin.
Water management complexity is underlined by the extent of floodable land, flood risk
and a recent steep increase in flood incidence ~ forecast to be exacerbated by climate
change ~ in the Severn Catchment. Severn-Trent Water manages its water resources,
taking a big chunk of mid-Wales out of Dŵr Cymru (Welsh Water) hands, whilst the
national Environment Agency has responsibility for flood management. Only two
reservoirs regulate discharge in the Cambrian Mountains and only one of these ~ Llyn
Clywedog, impounding a maximum of 11 billion gallons ~ was purpose-built in the
1960s to hold back flood peaks on the left-bank tributary River Clywedog, lowering
flood risk in Welshpool and Shrewsbury. The other, Llyn Vyrnwy, was constructed in
the 1890s for the city of Liverpool. The hydrographs of the rivers leaving both lakes are
inevitably quite different than those of adjacent upland catchments.
With no other flood-control reservoirs, and with much higher annual and intra-annual
flow variability that is suggested by mean discharge values alone, the floodplains
between Welshpool and Shrewsbury and Bewdley and Gloucester are amongst the most
flood-prone in Britain (Plate 5 and 6) and have experienced serious local or widespread
flooding in the past decade ~ none more so than in 2007. Rising river stage (depth) at
Bewdley is often taken as a marker for flood risk across England and Wales as a whole
and communities along the Severn corridor are implementing hard (permanent) and soft
(rapid-deployment and dismountable) flood defences (Plate 7). These are likely to be in
increased demand if and when forecast increases in the amount and intensity of British
precipitation kick in !
8
Plate 14.5 Flooding in the lower reaches of the Shrewsbury flood plain above Buildwas, looking towards
Ironbridge Gorge and the thermal power station. The power station makes a significant abstraction of
Severn water for cooling, much of which is lost to the atmosphere as steam. Photo: Ken Addison
Plate 14.6 The river Severn floods in Shrewsbury, December 2000, picking out the incised meander
around the medieval core of the country town of Shropshire, generated by high antecedent and intense
rainfall in its Welsh catchment. The upstream Welsh (centre left) and downstream Englidh (centre right)
bridges can be seen; the railway bridge crosses the river at the meander neck. Photo: by courtesy of the
Shropshire Star.
9
Plate 14.7 Temporary flood defences on the river Severn in Ironbridge, Shropshire, consisting of heavyduty polythene sheeting stretched over aluminium A frames, provides a cheap and rapid-response means
of protection at congested sites. Photo: Ken Addison.
Catchment hydrology data sources and their use
The principal UK hydrological data source is the National Water Archive (from which
the data summary above comes)~ comprising the National River Flow Archive and
National Groundwater Level Archive, maintained by the Centre for Ecology and
Hydrology’s base in Wallingford, Berkshire under the overall management of the UK’s
central government-funded Natural Environment Research Council. Other important
agencies include the UK Environment Agency, Environmental Data Index (UKED) and
catchment-specific management agencies or schemes (such as the Severn & Avon
Wetlands Partnership) and the UK Meteorological Office. Their data and graphics
enable, for example, comparative studies of the hydrographic data and river
hydrographs from different parts of the catchment, according to the location of gauging
station and the many meteorological, geological, land-use, river-network and
management variables across the catchment.
Learning Objectives
•
•
•
Explain the role of drainage basins characteristics, including those modified
by human activity, in converting precipitation into river discharge to the sea.
Appreciate how the processes of water and sediment transfer shape the
geomorphic character of individual river channels and the river networks of
the catchment.
Understand how any significant human socio-economic activity inevitably
changes hydrographic characteristics of the basin and may create water
management problems.
10
Essay titles
1. How do the cross- and long-sections of stream channels adjust to variations in
stream discharge, sediment load and potential energy?
2. Outline the likely impacts on stream flow, sediment yield and channel
morphology of a catchment due to changes in land use from woodland to arable
farming and then suburban development over the past century.
3. What may meandering, braiding and terracing by floodplain rivers tell us about
stream power and climatic change?
Discussion topics
1. Use the principal website data sources, together with appropriate topographic
and geological maps and UK Meteorological Office data, to explore and explain
Severn basin hydrographic characteristics ~ including short-term variability and
analysis of change over time.
2. Consider the rôle of the drainage network in the efficient evacuation of water
from a catchment.
3. After decades of straightening and smoothing river channels, why are many
rivers managers now seeking to reverse the changes?
Further Reading
Bridge, J.S. (2003) Rivers & Floodplains: Forms, Processes and Sedimentary Record.
Oxford: Blackwell Publishing. A richly-illustrated and comprehensive cover of
fluvial processes and landforms, bridging the interface between geomorphology with
useful sections on sedimentology and fluvial stratigraphic records.
Downs, P.W. and Gregory, K.J. (2004) River Channel Management: Towards
Sustainable Catchment Hydrosystems. London: Arnold. An excellent introduction to
the issues of sustainable channel/catchment management in the light of river channel
sensitivity and responsiveness to change.
Robert, A. (2003) River Processes: An Introduction to Fluvial Dynamics, London:
Arnold. A short but useful text, concentrating on river channel processes and channel
morphology rather than rivers and floodplains in any wider sense.
References
Boulton, G. S. (1992) ‘Quaternary’ in P. M. D. Duff and A. J. Smith (eds) Geology of
England and Wales, London: Geological Society, 413–44
Butzer, K. W. (1976) Geomorphology from the Earth, New York: Harper & Row
Department of the Environment Water Data Unit (1983) Surface Water: United
Kingdom, 1977–80, London: HMSO
11
Gregory, K. J. and Walling, D. E. (1973) Drainage Basin Form and Process: a
geomorphological approach, London: Arnold
Institute of Hydrology (1980) Low Flood Studies, Wallingford: Institute of Hydrology
Knighton, A. D. (1998) Fluvial Forms and Processes : a new perspective, London:
Arnold
Leeder, M. (1999) Sedimentology and Sedimentary Basins: From Turbulence to
Tectonics, Oxford: Blackwell Science
L’vovich, M. I. (1979) World Water Resources and the Future, Chelsea, MI: American
Geophysical Union
Mackay, G. A. and Gray, D. M. (1981) ‘The distribution of snow cover’ in D. M. Gray
and D. H. Male (eds) Handbook of Snow: principles, processes, management and
use, Toronto: Pergamon Press, 153–90
Newson, M. D. (1992) Land, Water and Development, London: Routledge
Newson, M. D. (1981) ‘Mountain streams’ in J. Lewin (ed.) British Rivers, London:
Allen & Unwin, 59–89
Ouichi, S. (1985) Response of alluvial rivers to slow active tectonic movement,
Geological Society of America Bulletin, 96. 504-515
Selby, M. J. (1985) Earth’s Changing Surface: an introduction to geomorphology,
Oxford: Clarendon Press
Strahler, A. N. and Strahler, A. H. (1992) Modern Physical Geography, New York:
Wiley
Ward, R. C. (1975) Principles of Hydrology, second edtion, London: McGraw-Hill
Ward, R. C. and Robinson, M. (2000) Principles of Hydrology, fourth edition, London:
McGraw-Hill
Web Resources
~ General UK Catchment
http://ceh.ac.uk/data/nrfa/index.html and
http://www.nerc-wallingford.ac.uk/ih/nwa/index.html
The principal websites for the Centre of Ecology & Hydrology (CEH), National Water
Archive (NWA) and National Water Flow Archive (NWFA), providing hyperlink
access and information on their component River Flow and Groundwater Archive of
data sets for British catchments. The aim of these UK Designated Data Centres is to
provide a focus for the Natural Environment Research Council's environmental holdings
and provide information and advisory services to a wide range of users. NWA data
holdings range from the catchment scale, eg detailed climatological and hydrological
data for a network of experimental catchments, to national (flood event data, annual
reviews) and international coverage (world flood archive). Onward linkages to other
data sets (including digitised rivers map, a Digital Terrain Model of the UK, hydrology
of soil types map, digital representation of average rainfall and evaporation records and
flood studies reports) can be made available by contacting the NWA. The access route
to these centres may change from time to time.
12
~ Severn Catchment-specific Web Resources
By intelligently navigating the principal websites above, it is possible to obtain maps,
data-sets, information, hydrographs, reports etc. for most river catchments in the UK. It
is not usually possible to go straight into the specific pages referenced below; instead,
entry through the entry web page opens a list of options and the particular ones to look
for ~ either on the entry page or click-on links listed there ~ are: River Flow Data :
Time Series Downloads. UK Gauging Stations Network (with click-ons → Regional
Maps → named and located gauging stations → their catchment details, descriptions,
data, sample hydrographs, gauged daily flows etc.).
The following related pages provide examples of useful types of data sets and graphics
you can find but they have to be searched for by title from the main sites, rather than
targeted directly. In other words, the page addresses below are the reference address,
not the search address.
http://www.nwl.ac.uk/ih/nrfa/webdata/eam.html
This specific web page consists of the Severn catchment in its series of UK catchment
maps, which also show the principal gauging stations for which other parts of the
overall website provide meteorological and hydrographic data. Clicking on any active
gauging station brings up station details.
http://www.nwl.ac.uk/ih/nrfa/river_flow_data/explanatory_notes.html
http://www.nwl.ac.uk/ih/nrfa/river_flow_data/about_the_data.htm
As these web addresses suggest, they provide useful summaries of what the NWA data
show and how to use them.
http://www.nwl.ih.nrfa.webdata/054001/g.html
This web page ~ of the River Severn at Bewdley, Worcestershire ~ shows the data
which is typically available for all individual gauging stations and includes local
catchment details affecting runoff, annual hydrographs continuously from 1921-2005
(for this station) and daily mean discharges with summary statistics for the most recent
complete year (2005).
http://www.environment-agency.gov.uk/regions/midlands/567079/567090/893833/89
The UK Environment Agency and the Department for Environment, Food and Rural
Affairs (DEFRA) open up other website opportunities to review, inter alia, flood-risk
areas and strategic approaches to river and flood management. This particular address
opens up their River Severn Strategies site.
Other Web Resources
http://www.environment-agency,gov.uk
The Environment Agency is the UK’s principal environmental protection organization,
with a wider brief than just rivers, river and coastal management and flooding.
Nevertheless, it is an excellent source of contemporary issues and events and provides
direct access to a wide range of data and information sources, government consultancy and
policy documents covering catchment and coastal management.
13
http://www.metoffice.gov.uk/ This accesses the homepage of the UK Meteorological
Office, the prime source of current and past weather data and related information and
services. The principal access to data records is
http://metoffice.gov.uk/education/index.html
http://www.epa.gov/OWOW
The United States Environment Protections Agency’s Office of Wetlands, Oceans and
Watersheds website, replicating for the USA many of the services and sources of
information on its field of responsibility as the UK Environment Agency. The website
provides a good balance of regional, national and international contemporary interest in
contemporary catchment management, conservation and protection issues.
http://www.iahs.info
The International Association of Hydrological Sciences (giving its English name)
promotes the study of all aspects of hydrology through the initiation of international
collaborative research and publication of results. As high-level research organization, its
principal value is to provide access to newsletters and reports of its various associated
International Commissions dealing with a wide range of hydrological fields including
Groundwater, Snow & Ice, Water Quality and Water Resources.
14