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.

1. 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.
2. The network should be a representative sub-sample of the inland water bodies of the EEA area.
3. 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 km² of 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.

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)

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.

1. 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.
2. 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.
3. Representative sites that can give a spatial and temporal general assessment of quality and quantity across Europe.
4. 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.
5. 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

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

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 of strata and sites could proceed through the following steps. The numbers of river reaches/river lengths meeting the criteria associated with each of the matrix cells in Tables 8.3 to 8.5 would be defined. This would ideally involve a comprehensive (probably GIS) database of the national river network. A reach here is defined as the portion of a river that meets the stream order criteria. Not all countries would have entries into each cell of the matrix. For example relatively flat countries would not have altitude categories a and b (Table 8.4) and some may not have reference sites.

As a first estimate ten percent of the river reaches/lengths would then be randomly selected. The current national monitoring site database would then be interrogated to determine how many and which sites appear in each of the selected reaches. In many cases it is likely that several sites would appear on the same reach. These may be located in relation to differences in quality along that reach. The most downstream site per reach should be selected provided that other criteria such as being downstream of mixing zones are met. Other reaches may not have any current sites at all. 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 representative site selection but would also be treated and selected separately as flux sites based on existing international requirements.

This procedure would potentially identify gaps, for example if current networks did not adequately cover all small headwater rivers or reference conditions. Where possible all existing national monitoring sites would be used.

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

8.2 Indicative example of site selection for rivers

Section 8.1 has described how a representative stratified monitoring network might be established for rivers and this should perhaps be the longer-term aim of the EEA network, and be developed as more information and experience is obtained to test the validity and practicalities of the design. In this section a stratified network is again suggested which could be used as the basis for developing the higher level network described in Section 8.1.

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

1. A basic network containing 1,781 rivers, made up of around 1,425 (80%) representative and 356 (20%) reference rivers. A reference river would be in a catchment with little or no human activity and the percentage of natural landscape would be higher than 90%. A representative river should reflect the majority of rivers in a region with human activities in the catchment consistent with the region’s activities. These rivers would be selected on the basis of 1 river site per 2,000 km² surface area. This density is that typically found across Europe (Kristensen and Bøgestrand 1996).
2. An impact network consisting of 1,588 rivers selected on the basis of population density such that in catchments with:
• < 50 inhabitants/km² there would be 1 river per 10,000 km², and
• between, 50 and 100 inhabitants/km², 1 river per 3,000 km^2, and,
• > 100 inhabitants/km², 1 river per 1,000 km^2.
3. The largest and most important rivers in the EEA area comprising approximately 650 in total. In the EEA area there are approximately 450 rivers with a catchment area greater than 2,500 km². In addition, the most important or well-known rivers/canals in each country should be included. These would also likely include those rivers currently monitored for the Exchange of Information Decisions (see Section 6.1.2).

4. 4. Flux stations. All monitoring information from those sites currently being used for the assessment of international transboundary loads or loads entering Europe’s 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 sites particularly those in relation to the work of HELCOM and OSPAR quantifying riverine loads entering the Baltic and North Atlantic (104 rivers), respectively. However, methodologies would have to be assessed to determine whether valid comparisons 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 country in a general surveillance network

Note:

NI No information

* Excluding flux stations and nationally large rivers not included in other categories

8.3 Selection of sites for surface water quantity monitoring network

Europe has a dense network of flow measurement stations, approximately 19,000 at an average density of 1 per 270 km². As has been indicated in an earlier section, it is recommended that a hierarchy of monitoring stations be established from which surface water quantity data can be obtained and these, where possible, should utilise existing national gauging networks. The hierarchy of stations is:

• Reference stations that characterise regimes in catchments undisturbed as far as possible by man.
• Baseline stations which, in total, characterise the generality of runoff behaviour of the region or country and whose data are appropriate for the transfer of hydrological characteristics to ungauged sites.
• Representative stations that are a subset of the network to provide summary estimates of the regional or national picture. Typically, these sites will have long records to provide a good historical perspective.
• Impact sites that record and characterise the effects of man's interference with the natural regime.
• Flux stations which when used in conjunction with water quality measurements can be used to quantify loads of contaminants entering Europe’s seas or crossing international boundaries. It is likely that this latter type of station may well also meet the criteria of some of the other stations and hence may serve a dual purpose.

The recommended types of monitoring station/site for 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 common aim but may not have to be synoptically located on the same river. In the case of impact sites there may be again a case for locating quality and quantity sites as close as possible. There appears to be no equivalence between the baseline stations which might have to be selected independently of surface quality stations. It would appear that the representative and impact sites would equate to the general surveillance sites from which supportive data would be acquired to identify sites with different impacts and levels of impact.

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

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

+ 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 frequency ranging from 4 to 26 samples per year. The statistical aspects of sampling frequency and sample numbers are discussed in Appendix A in particular in relation to how the information is to be reported. It is recommended that at least for the pilot implementation study that assessments are taken on data obtained over the whole year, spread approximately evenly over that period (e.g. monthly). In addition, long time series (monthly or more frequent) data should be obtained from a range of hydrological river types to assess relatively short term (e.g. monthly, seasonal) and longer term (yearly) variability. This would enable a more rational sample frequency to be established and take into account problems such as rivers drying out in summer in some countries.

8.5 Selection of determinants

The issues which the Agency may wish to address when determining the state of inland waters have been defined according to the following categories:

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

Table 8.8 lists the importance of the information required according to water type.

Through previous Tasks in the work programme it has been possible to identify determinants which would provide useful information for these categories. The determinants have been selected on the following basis:

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

Table 8.8 Information requirements for each water type

+++ 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

Table 8.9 (contd)