8. Proposed River Monitoring Network

8. PROPOSED RIVER MONITORING NETWORK

This section deals with the process by which sites could be selected by outlining the options that should be tested in the first phase of network implementation. It would be the intention that the site selection procedure would be modified where necessary in the light of experience gained in the pilot implementation during 1996. In addition, numbers of sites per station type have been given based on existing data sources, largely the review of current surface monitoring undertaken for DGXI and the Agency (Kristensen and Bøgestrand 1996).

The section has the following main recommendations.

The sampling sites to be included into the EEA network should be selected from the sampling sites in national monitoring programmes supplemented by additional sites to meet the requirement of the EEA. In cases where no national monitoring programmes exist, the sites to be included will, if possible, be selected from regional sampling sites.
The network should be a representative sub-sample of the inland water bodies of the EEA area.
The sampling sites to be included in the network should be selected so that they are representative of:

the size/numbers/types of water bodies in the EEA area (e.g. lake surface area);
the variation in human pressures (e.g. population density and land use);
and should include a number of reference and flux sites.

8.1 Definition of river and monitoring stations

8.1.1 Types of river

If a stratified network design is to be used then there are aspects of the target population (e.g. all rivers in Europe) that require definition and identification. First the types of water body to be sampled needs to be defined. At present the emphasis in many States appears to be on the sampling of the most important rivers, lakes and aquifers in terms of, for example, their size, status or use (e.g. for drinking water). These water bodies are likely to be a small proportion of the total river or lake population in terms of length or surface area. In some countries smaller rivers and streams, especially headwaters, may not be so intensively sampled even though headwaters are very important ecologically and some would be particularly susceptible to the effects of acidification. The combined length of small streams would also be a large percentage of the total river length in a country.

Definitions will often be somewhat arbitrary because one is trying to classify into compartments what is, in reality in most cases, a continuum of types not discrete packages. However, for the purposes of this network we have defined rivers as small, medium and large. Their selection would ideally be based on their appearance on a 1:50,000 scale map but, practically, for many States would relate to 1:250,000 maps which have been digitised for GIS. Size of rivers may also relate to flow, width, stream order, catchment area or altitude. There are advantages and disadvantages with each of these often interrelated descriptors. In addition, the information associated with many of the descriptors is often not readily available.

Stream order appears to be a good option but would require the consistent use of the same scale maps in site selection. The EEA have undertaken a pilot study on digitising Europe’s catchments on a 1:50,000 scale but such maps would not currently be available for most countries. Stream order (sensu Strahler) would then have to be defined on 1:250,000 scale maps. Small would equate to 1 to 3rd order, Medium to 4 or 5th order, and Large to 6th order or greater. Catchment area might also be a good indicator but there would be difficulty in defining a cut-off catchment area for small and medium rivers, for example. Also, catchment details may be missing for some countries. Altitude would be readily available from most maps and so it is suggested that for the pilot study rivers be to be characterised by a combination of stream order and altitude.

Morris and Kronvang (1994) estimated the river length for each country in the EEA area (using a sub-sample of areas from 1:50,000 maps where possible) (Table 8.1). On this basis, it was estimated that the EEA area contains approximately 2 million km of rivers which is equivalent to approximately 0.65 km per km²of the surface area of the EEA area. This estimate only applies to rivers significant enough to be mapped at 1:50,000 and artificial drainage ditches are excluded. The estimated river lengths from this study are generally 2 to 3 times greater than the countries report as the national river length. Ireland, for instance, reports its river length as 13,000 km compared to the 33,700 km estimate from the 1:50 000 maps.

Table 8.1 General characterisation of rivers and streams in the EEA area.

Country

Area

(km ² )

River length ¹

(L km)

Length per surface area (km-L per km ² )

River length given by countries

Number of river mouths ²

Austria	83,855	47,000	0.56	100,000	0
Belgium	30,519	22,600	0.74	NI	6
Denmark	43,092	28,000	0.65	62,000	281
Finland	338,145	159,000	0.47	20,000	526
France	547,026	563,000	1.03	273,000	370
Germany	357,000	179,000	0.50	NI	184
Greece	131,957	NI	NI	NI	352
Iceland	103,000	NI	NI	NI	NI
Ireland	70,285	33,700	0.48	13,000	341
Italy	301,268	136,000	0.45	NI	902
Luxembourg	2,586	1,330	0.51	NI	0
Netherlands	41,864	20,100	0.48	NI	27
Norway	324,219	210,000	NI	NI	1024
Portugal	91,949	172,000	1.87	NI	1137
Spain	504,782	172,000	0.34	NI	NI
Sweden	449,964	315,000	0.70	NI	702
United Kingdom	244,103	171,000	0.70	53,500	1362

EEA Area

3,665,614

2,200,000

0.65

7200

Notes:

NI No information

1 Based on 1:50,000 maps;

2 From Morris and Kronvang (1994) based on 1:200,000 or 1:250,000 maps

Table 8.2 gives an estimate of the number of rivers in the EEA area (excluding Iceland) with catchments of specified sizes. These could be used to stratify sampling sites according to the size of catchment area.

Table 8.2 Estimated distribution of rivers according to catchment area (based on estimates from Morris and Kronvang, 1994)

Catchment area (km ² )

Number of rivers in the EEA area

>10,000	123 to 140
>5,000	280
>2,500	420 to 490
>1,000	800 to 1,200
>500	1,000 to 2,500
>250	1,500 to 4,200
>100	10,000

8.1.2 Types of monitoring site

The need for different types of monitoring site or station has been discussed in Section 4, and for the purposes of this section the following station types have been used.

Reference sites located on rivers in natural catchments with little or no human activity and with greater than 90% natural landscape. It is likely that such sites will not be present in some parts of Europe.
Baseline stations in the context of surface water quantity monitoring which may be required to characterise the generality of run-off behaviour of the region or country.
Representative sites that can give a spatial and temporal general assessment of quality and quantity across Europe.
Impact sites could form part of the representative network for the collection of supportive and interpretative information, or could form separate impact strata within which sites could be randomly selected. Impact networks could reflect general human activities, for example, urbanisation and agriculture, or more specific impacts such as acidification or saltwater intrusion into aquifers.
Flux sites established where rivers discharge into sea, or cross-national boundaries, or there is interchange between surface and groundwater.

8.1.3 Examples of stratification options for rivers

Table 8.3 illustrates how a river-sampling network might be stratified to provide information on the general quality of small, medium and large rivers. As described in previous sections there would also be a need for reference sites which would be selected randomly from all rivers that met the reference criteria. Flux sites would be selected on the basis of location in relation to VALIGN="TOP">

Representative

Flux

The sites representative of general quality identified in Table 8.3 could be established and later divided into different types of impact sites based on the supportive information gathered, e.g. land-use, catchment altitude, population density. The disadvantage here would be if areas impacted by different human activities were over or under representatively sampled. An additional layer or stratum could be added if part of the target population was not being representatively sampled, for example, a stratum based on altitude. Such a potential stratification is shown in Table 8.4. This should ensure that upland and lowland headwaters were representatively sampled.

The next, higher, level of definition of strata (Table 8.5) might include differentiation between impacted and non-impacted sites, and within impacted sites between different causal activities, land-use, population etc. Each additional strata would increase the need for supportive information by which the target population can be defined, and for definitions such as what population density represents an urbanised catchment, what proportion of agricultural use a predominately agricultural catchment, the predominant agricultural use, a forested catchment. These definitions would require the assistance of other EEA Topic Centres and may require revision in the light of experience with the network developed during pilot implementation.

Table 8.4 Potential mid-level stratification of rivers into target populations for sampling

Type of

monitoring site

Relative size

(1:250,000)

small rivers

(1 to 3rd order)

medium rivers

(4 to 5th order)

large rivers

(6th order and above)

Relative European altitude

(class)

Reference

Representative

Flux

Altitude classes: a = >800m, b = 500 to 800m, c = 200 to 500m, d = 100 to 200m, e = <100m

Within impact networks there may also be a case of establishing upstream and downstream sites for comparison purposes. This would be relatively straightforward in the case of large towns and cities but more difficult for more diffuse sources such as from agricultural land. In the latter case they might be established where there is a significant change in land-use. In all cases sites should be located downstream of point sources of contaminants e.g. sewage works discharges and at a point where the effluent has become fully mixed within the flow, in other words downstream of the mixing zone. The latter varies with river discharge and as such should be established at the worst case conditions. Europe’s largest and most important rivers would presumably be included in the flux stations as most would be industrialised and urbanised and potentially the most polluted.

There may also be a case for stratification on a regional basis reflecting biogeographic or hydrological regions of Europe.

Table 8.5 Potential high level stratification of rivers into target populations for sampling

Type of

monitoring site

Relative size

(1:250,000 map)

small rivers

(1 to 3rd order)

medium rivers

(4 to 5th order)

large rivers

(6th order and above)

Relative European altitude

(class)

Catchment/reach characteristics

Reference or baseline

natural
(little or no human activity, >90% natural landscape)

Representative sites divided according to type/source of impact

- Impact

urbanised

a) with towns

> 2,000 inhabitants or

>50 inhabitants/km ²

b) heavily urbanised >100,000 inhabitants or >100 inhabitants/km ²

- Impact

rural ^- with towns

< 2,000 inhabitants

< 50 inhabitants/km ²

- Impact

agricultural

- Impact

forested

Flux

Tidal limits, transboundary rivers, lakes

Altitude classes

a = >800m, b = 500 to 800m, c = 200 to 500m, d = 100 to 200m, e = <100m

8.1.4 Selection of strata and sites

In the approach described above the selection ofstrata and sites could proceed through the following steps. The numbersof river reaches/river lengths meeting the criteria associated with eachof the matrix cells in Tables 8.3 to 8.5 would be defined. This would ideallyinvolve a comprehensive (probably GIS) database of the national river network.A reach here is defined as the portion of a river that meets the streamorder criteria. Not all countries would have entries into each cell ofthe matrix. For example relatively flat countries would not have altitudecategories a and b (Table 8.4) and some may not have reference sites.

As a first estimate ten percent of the river reaches/lengthswould then be randomly selected. The current national monitoring site databasewould then be interrogated to determine how many and which sites appearin each of the selected reaches. In many cases it is likely that severalsites would appear on the same reach. These may be located in relationto differences in quality along that reach. The most downstream site perreach should be selected provided that other criteria such as being downstreamof mixing zones are met. Other reaches may not have any current sites atall. These gaps would be noted, and if possible as an interim measure,sites from similar reaches would be selected.

Flux sites should be included in the representativesite selection but would also be treated and selected separately as fluxsites based on existing international requirements.

This procedure would potentially identify gaps, forexample if current networks did not adequately cover all small headwaterrivers or reference conditions. Where possible all existing national monitoringsites would be used.

As an alternative to selecting river lengths or reaches,existing national or regional monitoring sites could be selected by thestrata criteria. This would not give such a representative view of totalriver resources but might be more easily implemented in the short term.However, there would be a need to fill these gaps in progressively as thenetworks change to become more representative.

8.2 Indicative example of site selection for rivers

Section 8.1 has described how a representative stratifiedmonitoring network might be established for rivers and this should perhapsbe the longer-term aim of the EEA network, and be developed as more informationand experience is obtained to test the validity and practicalities of thedesign. In this section a stratified network is again suggested which couldbe used as the basis for developing the higher level network describedin Section 8.1.

A general surveillance network to obtain informationon the general quality of rivers would consist of:

A basic network containing 1,781 rivers, made upof around 1,425 (80%) representative and 356 (20%) reference rivers. Areference river would be in a catchment with little or no human activityand the percentage of natural landscape would be higher than 90%. A representativeriver should reflect the majority of rivers in a region with human activitiesin the catchment consistent with the regions activities. These riverswould be selected on the basis of 1 river site per 2,000 km ² surfacearea. This density is that typically found across Europe (Kristensen andBøgestrand 1996).
An impact network consisting of 1,588 rivers selectedon the basis of population density such that in catchments with:

< 50 inhabitants/km ² there would be 1 river per 10,000 km ² , and
between, 50 and 100 inhabitants/km ² , 1 river per 3,000 km ^2, and,
> 100 inhabitants/km ² , 1 river per1,000 km ^2.

The largest and most important rivers in the EEAarea comprising approximately 650 in total. In the EEA area there are approximately450 rivers with a catchment area greater than 2,500 km ² . Inaddition, the most important or well-known rivers/canals in each countryshould be included. These would also likely include those rivers currentlymonitored for the Exchange of Information Decisions (see Section 6.1.2).
4. Flux stations. All monitoring information fromthose sites currently being used for the assessment of international transboundaryloads or loads entering Europes Seas should be included in the network.Some of these are likely to correspond to those included in (3) above.There are obviously prime sources of existing information for these sitesparticularly those in relation to the work of HELCOM and OSPAR quantifyingriverine loads entering the Baltic and North Atlantic (104 rivers), respectively.However, methodologies would have to be assessed to determine whether validcomparisons could be made or, at least, any differences identified.

This potential network in summarised in Table 8.6.

Table 8.6 Approximate number of rivers per countryin a general surveillance network

Country

Area

(km ² )

Representative rivers

1 per 2,000 km ²

Impact rivers

Total*

Austria	83,855	42	38	80
Belgium	30,519	15	31	46
Denmark	43,092	22	17	39
Finland	338,145	169	41	210
France	547,026	272	230	502
Germany	357,000	179	357	536
Greece	131,957	66	34	100
Iceland	103,000	51	NI	at least 51
Ireland	70,285	35	23	58
Italy	301,268	151	283	434
Luxembourg	2,586	1	3	4
Netherlands	41,864	21	40	61
Norway	324,219	162	33	195
Portugal	91,949	46	47	93
Spain	504,782	253	161	414
Sweden	449,964	225	59	284
United Kingdom	244,103	122	191	313

EEA Area

3,665,614

1,832

1,588

3,420

Note:

NI No information

* Excluding flux stations and nationally large riversnot included in other categories

8.3 Selection of sites for surface water quantitymonitoring network

Europe has a dense network of flow measurement stations,approximately 19,000 at an average density of 1 per 270 km ² .As has been indicated in an earlier section, it is recommended that a hierarchyof monitoring stations be established from which surface water quantitydata can be obtained and these, where possible, should utilise existingnational gauging networks. The hierarchy of stations is:

Reference stations that characterise regimes incatchments undisturbed as far as possible by man.
Baseline stations which, in total, characterisethe generality of runoff behaviour of the region or country and whose dataare appropriate for the transfer of hydrological characteristics to ungaugedsites.
Representative stations that are a subset of thenetwork to provide summary estimates of the regional or national picture.Typically, these sites will have long records to provide a good historicalperspective.
Impact sites that record and characterise the effectsof man's interference with the natural regime.
Flux stations which when used in conjunction withwater quality measurements can be used to quantify loads of contaminantsentering Europes seas or crossing international boundaries. It is likelythat this latter type of station may well also meet the criteria of someof the other stations and hence may serve a dual purpose.

The recommended types of monitoring station/sitefor surface quantity and quality monitoring are compared in Table 8.7.Some types would ideally be synoptically located as close together as possible,for example for flux/load determinations. Others appear to have a commonaim but may not have to be synoptically located on the same river. In thecase of impact sites there may be again a case for locating quality andquantity sites as close as possible. There appears to be no equivalencebetween the baseline stations which might have to be selected independentlyof surface quality stations. It would appear that the representative andimpact sites would equate to the general surveillance sites from whichsupportive data would be acquired to identify sites with different impactsand levels of impact.

It is recommended for the pilot implementation ofthe network that the same selection procedure be applied to the surfacequantity network as for the river quality network. Where possible qualityand quantity sites would be selected at the same location or at least onthe same river reaches. Baseline sites should be selected independently.The numbers and density of stations should be based on the variabilityof the systems being monitored and the desired precision and confidenceof the information supplied.

Table 8.7 Comparison of types of monitoring station/sitefor surface quantity and quality monitoring

Surface quantity

Reference

Baseline

Representative

Impact

Flux

Surface quality

Reference	@	¥	¥	¥	¥
Representative	¥	¥	@	@	¥
Impact	¥	¥	@	+	¥
Flux	¥	¥	¥	¥	+

+ synoptic sites

¥ no overlap

@> equivalent purpose,though specific sites may not have to be synoptic

8.4 Sampling frequency

According to the inventory of river quality monitoring(Section 5.2.1) most monitoring is undertaken annually with a sample frequencyranging from 4 to 26 samples per year. The statistical aspects of samplingfrequency and sample numbers are discussed in Appendix A in particularin relation to how the information is to be reported. It is recommendedthat at least for the pilot implementation study that assessments are takenon data obtained over the whole year, spread approximately evenly overthat period (e.g. monthly). In addition, long time series (monthly or morefrequent) data should be obtained from a range of hydrological river typesto assess relatively short term (e.g. monthly, seasonal) and longer term(yearly) variability. This would enable a more rational sample frequencyto be established and take into account problems such as rivers dryingout in summer in some countries.

8.5 Selection of determinants

The issues which the Agency may wish to address whendetermining the state of inland waters have been defined according to thefollowing categories:

ecological quality;
acidification;
nutrient status;
pesticides;
heavy metals;
organic pollution;
pathogens;
water availability;
physical intervention.

Table 8.8 lists the importance of the informationrequired according to water type.

Through previous Tasks in the work programme it hasbeen possible to identify determinants which would provide useful informationfor these categories. The determinants have been selected on the followingbasis:

they are commonly measured under international agreements;and/or,
they are commonly measured in national programmes.

Table 8.8 Information requirements for each watertype

Information required

Rivers

Lakes

Groundwater

ecological quality;	+++	+++
acidification;	+++	+++	+++
nutrient status;	+++	+++	+++
pesticides	++	++	+++
heavy metals;	+++	++	+++
organic pollution;	+++	++	++
pathogens;	+++	++	++
water availability	+++	+	+++
physical intervention.	+++	++

+++ Key

++ Important

+ Useful

Table 8.9 lists the suggested primary determinants, that is those that are essential, and secondary determinants, that is those which would be useful but not essential, that would provide useful information to answer specific problems or issues. It should be noted that pesticides, other synthetic organic substances and heavy metals would be selected on the basis of their use in the catchment of interest.

Supportive determinants used to interpret the information listed above for example, salinity when measuring DO in estuaries, land-use, population in catchment will also be required. It is recommended that other Topic Centres, such as that on Land Cover, are consulted about which indicators are most appropriate for quantifying human activities.

Table 8.9 List of suggested primary and secondary determinants required for the river and lake monitoring networks

Indicator determinants ¯	Problems/issues ®	EQ	AC	NS	TS	OP	WU	RA	PI	FL
	++	+++	+++	+	++	++ (ss)
Flow	Flows, levels	+++	++	++	++	++	+++	+	+++	+++
Additional determinants	Biochemical oxygen demand Chemical oxygen demand Total organic carbon, Secchi disc, Aluminium fractions	++	+++	++	+	+++	++	+	+	+
Nutrients	Total phosphorus, Soluble reactive phosphorus, Nitrate Nitrite, Ammonia, Organic nitrogen, Total nitrogen	++	+	+++	+	++	+	+	+	+++

Table 8.9 (contd)

Indicator determinants ¯	Problems/issues ®	EQ	AC	NS	TS	OP	WU	RA	PI	FL
	Examples of indicators ¯

Major ions	Calcium, Sodium, Potassium, Magnesium, Chloride, Sulphate, Bicarbonate	+	+++	+	+	+	++	+	+	+
Heavy metals	Cadmium, Mercury Based on catchment/land-use	+	+	+	++	+	++	+	+	++
Pesticides	Based on catchment/land-use	+	+	+	+++	+	++	+	+	+++
Other synthetic organic substances	PAH, PCBs Based on catchment/land-use	+	+	+	+++	+	++	+	+	+++
Microbes	Total and faecal coliforms, Faecal streptococci, Salmonella, Enteroviruses	+	+	+	+	+++	++	+	+	+
Radionuclides	Total alpha and beta activity Caesium 137	+	+	+	+	+	+	+++	+	++

Key to problems/issues	Key to importance:
EQ Ecological quality	+++ Key determinants - primary
AC Acidification	++ Important but not key determinants - secondary
NS Nutrient status	+ Not considered as essential
TS Toxic substances
OP Organic pollution Other:
WU Water use and availability ss Suspended solids
RA Radioactivity
PI Physical intervention
FL Fluxes