Welcome to the Hydro-Data website
provided by the
Office of Public Works

1. INTRODUCTION

The Hydro-Data website provides you with quick and easy access to hydrometric data that has been collected and processed by the Office of Public Works (OPW) for over 70 years. The Hydro-Data website was first published in 2013 and replaces the www.opw.ie/hydro website in use since 2002. It is planned to change the point of data dissemination from the old website to the new website on a phased basis, with station data withdrawn from the old website as it is posted on the new website.

There are currently 386 surface water stations in the OPW hydrometric surface water network. It is planned to disseminate all of these station datasets via the Hydro-Data website upon completion of data preparation works. In addition, inactive station datasets will also be made available. The data disseminated will include a range of hydrometric data types, including water levels, estimated flows, summary statistics, and station related meta data. 

If you require data at a location that is not available on this website, then you might contact the Environmental Protection Agency (EPA - www.epa.ie) which also maintains a database of hydrometric information from stations at other locations.

It is important that you read carefully all of the notes provided below. Having read the information provided, you may proceed to viewing and downloading the data by acknowledging the notes and agreeing to certain conditions of use by clicking the ‘Yes’ button provided at the bottom of the page.

If you have any queries or comments concerning the use of the site or the data provided, please contact our staff in the Hydrometric Section of the OPW, by Email at hydrometric@opw.ie, or by telephone on: 093 35456 / 36372.

2. HOW TO USE THE SITE

Explained below is how to find, view and output the data you need. The site has been developed to help first-time users find the information they need, and further guidance notes are provided on the subsequent pages, but if you are having any difficulties, please feel free to contact our staff as noted above.

Once you have read the notes below and agreed to the conditions of use of the data, you will be able to view or download data by first selecting a particular hydrometric station.

A station window presenting available data on a number of station tabs can be selected from a number of options including:

Search / Query: The station can be selected by using the search / query box to search by criteria such as station name, number, river, catchment or River Basin District (RBD).

Station Lists: A full list of stations can be obtained by selecting the ‘Stations’ or ‘Measurements’ headings from the menu bar. The ‘Stations’ or ‘Measurements’ options will provide a complete list of available stations presented as either a Table or Map view. The view can be selected by the tab headings.

Station Maps: Stations within a particular River Basin District (RBD) can be selected via the map on the homepage. Again this will provide a complete list of stations within the selected RBD. As above, this will provide a complete list of stations within the selected RBD presented as either a Table or Map view.

The station data can be selected by clicking on the representative station line or map node. Once the station window has been opened, available data is presented on range of tabs including:

Parameter: Presents instantaneous water level, flow and water temperature data graphically for the last week, month or year together with significant thresholds and statistics eg, percentiles and significant flood data.

Metadata: Presents a range of station related information including Station Number, Station Name, Location (Lat / Long), River, Catchment, Catchment Size (Area), River Basin District (RBD), Station Status, Longterm average flow value, Station type, Diary entries (for disseminating station specific notes), Station Description and a number station photographs (with text explanation).

Statistics: See notes on Summary Statistics under 4.2 below.

Annual Max: See notes on annual maxima series under 4.3 below.

Duration curve: See notes on Summary Statistics under 4.2 below.

Download: Data available for download is available in a number of different formats including instantaneous records and daily mean records of water level, flow and water temperature (where available). A record of water level calibration checks is also available to facilitate user validation of unchecked data.

Owing to the size of the files created, the complete records are only updated on a monthly basis, with the most recent data updated in separate files twice daily. The two files can be appended by the user to create a full record.

The download files have been created in text format but have been zipped or condensed to facilitate faster download. To open the files, the files will first need to be unzipped from the downloaded file. The data can then be viewed using a range of commonly used programmes.

3. DATA COLLECTION PROCESS

Provided below for information is a brief description of the equipment and methodologies that have been used in collecting and processing the hydrometric data that is available on the site.

3.1 Water Level Recording

The water level data is collected using data loggers and historically using autographic recorders.

An autographic recorder provides a continuous trace of water level on weekly or monthly charts (piece of graph paper approximately A3 in size) using a float and weight system which moves a pen on a spindle via a pulley and gearing mechanism. The water level trace on the charts is then digitised to provide a ‘time-series’ of water level against time.

A data logger digitally records the water level at set time intervals converting the water level using a pressure transducer immersed into the water body.

The water levels are recorded as water depths (stage) above a staff gauge zero level. A staff gauge is a graduated plate that allows our Field Technicians to manually check that the correct water level is being displayed on the recording devices, and hence validate the data recorded. The zero level of the staff gauges have been surveyed to either Poolbeg or Malin Head Ordnance Datum levels, and these heights are added to the recorded levels (stage) to provide water levels to an Ordnance Datum. It is important that you check which datum level is being used for each site accessed.

The equipment can malfunction or breakdown, and there are therefore gaps in the records provided. These are indicated by a certain quality code (see below), and must be considered when evaluating the data, and in particular peak or low water levels or flows.

3.2 Flow Estimation

The OPW does not continuously record river flow, but rather estimates it from ratings (stage-discharge relationships) and the recorded water levels.

A rating is a relationship that equates a given water level to a given flow at a particular location. It is developed from a series of flow gaugings taken at the monitoring sites (see below). By applying the rating to the water level time-series it is possible to estimate a flow time-series which can then be manipulated to provide data such as daily mean flows, or flow duration statistics.

During a flow gauging, the velocity is measured at a series of points across the river from which the flow is calculated for the water level at that time. This is the velocity-area method of measurement (see ISO748 / BS3680). A flow gauging is hence a spot calculation of flow (discharge) for a given level (stage). Using a series of such gaugings over a range of water levels, it is possible to derive an equation for the line-of-best-fit through the scatter of gaugings, which effectively describes the relationship at that location between the stage and discharge, i.e., a stage-discharge relationship, or rating as they are commonly known.

A fundamental assumption of the use of ratings to generate flow estimates is that the relationship between stage and discharge remains constant in time. This is not always the case. Seasonal weed-growth, sedimentation, erosion, drainage, variable structures (such as locks or sluices) or construction work in the channel or floodplain can all change the control that determines level for a given flow. Other water bodies downstream, such as lakes, larger rivers and indeed the sea can backwater the monitoring site and so the level is dependent on factors other than the flow at the gauging location. At fully tidal sites, the level is generally independent of the flow and so there is effectively no relationship between level and flow. These effects and phenomena have a number of impacts:

§                     it is not possible to derive an adequate rating at some stations, and so while water levels are recorded and provided on this website, flow data will not be available at all stations,

§                     the ratings at most sites can change with time, and so ratings can therefore be extrapolated in time in the absence of recent flow gaugings, and might be changed retrospectively by the OPW should further data come to light, and so flow estimates for a given date can be subject to revision:.

§                     whenever a rating is extrapolated in time, a provisional ratings is applied to cover the period of estimated flow data from last assessment of the rating up to the current time. Certain quality codes are attached to such data (see below), which must be treated as potentially erroneous and hence with caution,

§                     ratings at stations subject to frequent but minor changes in control can have a significant degree of scatter of gauging points around the rating, and hence a high margin of error, and so estimated flow data at these sites should be treated with caution (see quality codes below).

The ratings are developed from flow gaugings (as described above) over the range of water levels for which flow gaugings have been (or can be) taken at that station. Frequently this range does not cover the entire range of levels (and hence flows) that can occur. Where levels occur that are outside of the gauged range, flows are estimated using a direct extrapolation of the rating equation. In some instances this might be appropriate, but this is certainly not always so. Whenever an extrapolated rating is used, certain quality codes are attached to the data (see below), which must be treated as potentially erroneous and hence with caution.

It is important to remember that the flow data provided is estimated and can contain a significant degree of uncertainty due to the scatter in flow gaugings around the rating equation and changes of control in time. The flow data provided should therefore only be used with due consideration given to the above warnings and the quality codes attached.

You might note that a range of flow data statistics (low flow statistics in particular) for a number of stations around Ireland are available from the EPA website.

4. DATA TYPES

The various types of data that are available on this website are outline below, together with particular points that should be noted in relation to potential problems with data reliability.

4.1 Average Annual Mean Values (Summary Statistics)

These values are the mean values of flow or water level as calculated over a period of full years.

It should be noted that the values might be skewed under the following circumstances:

§                     the period of record was abnormally wet or dry,

§                     significant gaps in the records have occurred during low or high flow periods,

§                     inappropriate extrapolation of ratings has been used (flow data only).

4.2 Duration Percentiles (Summary Statistics)

These are values of flow or water level that are equalled or exceeded for the given percentage of time.

It should be noted that these values can be skewed for the same reasons as those given under 4.1, and for extreme percentiles, the last of the reasons given is particularly relevant. It should also be noted that for flashy catchments, percentiles derived from daily mean values may be skewed.


4.3 Daily Mean Values

These are the mean values of flow or level as calculated for each day.

4.4 Annual Maxima Values

These are the highest recorded water levels or estimated flows in each available hydrometric year of record. A hydrometric year runs from 1st October in the given year to the 30th September the following year, i.e., the hydrometric year 2010 runs from 1st October 2010 to 30th September 2011.

As noted above, there are gaps in the record due to logger or autographic recorder malfunction, missing charts, etc. It is therefore possible that the water levels (and estimated flows) in any given year may have exceeded the maximum value given for that year, and indeed that the maximum given for the period of record may have been exceeded during that period.

The majority of estimated annual maxima flows have been derived from extrapolated ratings (see 3.2). Where this is the case, the data may be erroneous and should be treated with caution. Note however that quality codes are not attached to annual maxima data, and reference should therefore be made to the ‘reliable limit’ values specified for each series.

5. DATA

5.1 Introduction to Quality Codes

Quality codes provide an indicative measure of the reliability and confidence placed on each item of data, and can appear numerically or as a symbol, depending on the format of the data. It should be noted that the majority of the codes are allocated following certain criteria but are subjective, and are not associated with any given confidence limits in terms of percentage, absolute value or standard error. The codes should therefore be used only as an indication of the reliability of the data, and must not be used in any way as justification to waive or forgo any independent verification process appropriate to the proposed use of the data.

5.2 Table of Quality Codes

Code

Symbol

Description

WATER LEVEL DATA

1

*

Unchecked digitised water level data – Data is provisional only and must be used with caution

31

  31

Inspected water level data – Data may contain some error, but has been approved for general use

32

C

As per Code 31, but where the digitised water level data has been corrected

99

*

Superseded quality code, see code 254. Unchecked imported water level data – Data is provisional only and must be used with caution

145

<

Data is below prescribed data range and must only be used with caution

146

>

Data is above prescribed data range and must only be used with caution

150

I

Partial statistic – Data has been derived from records that are incomplete and do not necessarily represent the true value

101

!

Unreliable water level data – Data is suspected of being erroneous or is artificially affected (e.g., during drainage works) and must only be used with caution

>150

Various

Data is not available as it is missing, erroneous or of unacceptable quality

254

*

Unchecked imported water level data – Data is provisional only and must be used with caution

ESTIMATED FLOW DATA

31

  31

Flow data estimated using a rating curve that it is considered to be of good quality and inspected water level data – Data may contain some error, but is considered to be of acceptable quality for general use

32

C

As per Code 31, but using water level data of Code 32

36

F

Flow data estimated using a rating curve that it is considered to be of fair quality and inspected or corrected water level data – Data may contain a fair degree of error and should therefore be treated with some caution

46

B

Flow data estimated using a rating curve that it is considered to be of poor quality and inspected or corrected water level data – Data may contain a significant degree of error and should therefore be used for indicative purposes only

56

X

Flow data estimated using an extrapolated rating curve (see Section 3.2) and inspected or corrected water level data – Reliability of data is unknown and it should therefore be treated with caution

96

P

Flow data estimated using a provisional rating curve – data may be subject to revision following retrospective assessment of rating curves with the most recently taken flow measurements

99

*

Superseded quality code, see code 254. Flow data that has been estimated using unchecked water level data – Data is provisional only and must be used with caution

101

!

Flow data that has been estimated using unreliable water level data – Data is suspected of being erroneous and must only be used with caution

145

<

Data is below prescribed data range and must only be used with caution

146

>

Data is above prescribed data range and must only be used with caution

150

I

Partial statistic – Data has been derived from records that are incomplete and do not necessarily represent the true value

>150

Various

Data is not available as it is missing, erroneous or of unacceptable quality

254

*

Flow data that has been estimated using unchecked water level data – Data is provisional only and must be used with caution

Please note that quality codes are only associated with daily mean values text files and reports, and will be displayed either as a code (text files) or a symbol (reports). The quality codes are not displayed on hydrograph plots, and so reference should be made to either text files or reports for an indication of data quality. The reliability of annual maxima and summary statistic data is indicated on the relevant page.

5.3 Independent Verification

The operations of the Hydrometric Section of the OPW are quality assured and have been certified under ISO 9001: 2008 by the National Standards Authority of Ireland. While the quality management procedures include quality control of data, this does not guarantee accuracy, and you must undertake any independent quality control and verification procedures appropriate to the proposed use of any data taken from this website. To this end, unprocessed and source data are available for inspection on prior arrangement at our offices in Headford, Co Galway. To arrange to inspect the data, you can contact our staff using the Email address or telephone numbers given under section 1 above.

6. USERS DECLARATION

Please read carefully the following statements and conditions of use of the data. Proceeding to data viewing and retrieval by clicking on the ‘Yes’ button denotes agreement to, and unconditional acceptance of, all of the statements and conditions.

I have read in full, understand and accept all of the above notes and warnings concerning the source, reliability and use of the data available on this website.

I agree that the Commissioners of Public Works have the absolute right to reprocess, revise, add to, or remove any data available on this website as they deem necessary, and that I will in no way hold the Commissioners of Public Works liable for any damage or cost incurred as a result of such acts.

I will use any data available on this website in an appropriate and responsible manner and in accordance with the above notes, warnings and conditions.

I understand that the Commissioners of Public Works do not guarantee the accuracy of any data available on this website, and it is my responsibility to independently verify and quality control any of the data used and ensure that it is fit for use.

I will not pass on any data used from this website to any third party without ensuring that said party is fully aware of the notes, warnings and conditions of use.

I accept all responsibility for the use of any data available on this website that is downloaded, read or interpreted or used in any way by myself, or that is passed to a third party by myself, and will in no way hold the Commissioners of Public Works liable for any damage or loss howsoever arising out of the use of interpretation of this data.

Do you agree to all of the above statements and conditions of use?