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It is important that you read carefully all of the notes provided below. If you have any queries or comments concerning the use of the FSU Web Portal or the related data, then please read these FAQs first before contacting the OPW FSU Helpdesk Team.

1. About the FSU Programme 
Q: What is the FSU Programme?
A: The FSU Programme is a programme of research and development, undertaken by the Office of Public Works (OPW), to provide improved methods of extreme rainfall and flood estimation at both gauged and ungauged river locations in the Republic of Ireland. It is a substantial update of a programme of study called the Flood Studies Report (FSR) (NERC, 1975), which was undertaken in the early 1970s by organisations in Ireland and the United Kingdom (UK) to provide methodologies for flood estimation in Ireland and the UK. The outputs from the FSU Programme are now implemented with this Portal as a free-to-use suite of online design tools. 

Q: Why was the FSU Programme undertaken?
A: The Flood Studies Report (FSR) (NERC, 1975) has been the recognised suite of methods used in Ireland for estimating extreme rainfalls and floods. In 1999 the Flood Estimation Handbook (FEH) (Institute of Hydrology, 1999) superseded the FSR in the UK. Considering the large amount of extra data and improvements in technology and methods since 1975 it was recognised that a similar update of extreme rainfall and flood estimation methodologies for Ireland was required.

Q: When did the FSU Programme start?
A: The Irish Government approved the Report of the Flood Policy Review Group in September 2004. The report included a recommendation for an update of the Flood Studies Report (FSR) (NERC, 1975) for Ireland, which became known as the FSU Programme. In 2005 the first research work began under the FSU Programme.

Q: How long did the FSU Programme take to undertake?
A: The research work under the FSU Programme was completed in 2011 (a total of 17 research projects were undertaken).
Since 2011 the focus has been on organising this research into a suite of methodologies for implementation in the FSU Web Portal.

Q: How was the FSU Programme managed?
A: The FSU Programme was managed in-house by Engineering Services Division of the OPW. 

Q: Who provided technical input / advice to the FSU Programme?
A: In early 2005, a Technical Steering Group (TSG) chaired by the OPW took on the role of specifying and managing the technical aspects of the FSU Programme.  The TSG was made up of a number of experts from the OPW, EPA, Met Éireann, ESBI, NUI Galway, and included Professor Con Cunnane and Dr. Duncan Reed who were centrally involved in the development of the Flood Studies Report (FSR) (NERC, 1975) and Flood Estimation Handbook (FEH) (IH, 1999) methodologies respectively. Dr. Duncan Reed was retained as the external Technical Advisor for the duration of the FSU research, and provided expertise in specifying the research to be commissioned and the review of that research. Dr. Reed also was responsible for editing four of the Volumes of the FSU Technical Research Reports. Technical input / advice was also required in relation to the development of the FSU Web Portal in order to effectively disseminate the programme outputs and this was provided by the FSU Web Portal Steering Group comprising members of the OPW, RPS Group and HydroLogic BV.

Q: What are the expected benefits to the State of completing the FSU Programme?
A: The methodologies provided by the FSU Programme will allow improved estimation of design flows at all gauged and ungauged river locations in the country. This will lead to efficiencies in the design of flood relief schemes, roads, bridges, commercial and housing development, and other infrastructure. The outputs of the FSU Programme will also be incorporated into flood mapping and catchment flood risk management plans. These plans will ultimately inform planning and development policy in the future. The Physical Catchment Descriptors (PCDs) developed through the FSU Programme are already being used for other non-flood related applications.
Q: Were users / stakeholders consulted in the development and implementation of the FSU Programme?
A: Three separate stakeholder consultation workshops were undertaken in June 2007 (in Galway, Cork and Dublin) to assess the needs of those who would eventually become users of the FSU methodologies. In response to the feedback received at the consultation days, some further research work packages were added to the FSU Programme. In the later stages of the programme, a selected group of prospective users was chosen to carry out Alpha and Beta testing of the FSU Web Portal. The feedback received from this testing was further used to inform the final design of the Portal.

2. About the FSU Research 
Q: What organisations / bodies undertook the FSU research?
A: The organisations that carried out the FSU research were as follows:
  • Office of Public Works         (3 Work Packages)
  • JBA Consulting                     (2 Work Packages)
  • Met Éireann                           (2 Work Packages)
  • NUI Galway                           (2 Work Packages)
  • University College Dublin       (2 Work Packages)
  • Compass Informatics            (1 Work Package)
  • DWRconsult                          (1 Work Package)
  • Hydro-Logic Services          (1 Work Package)
  • NUI Maynooth                       (1 Work Package)
  • RPS Group                            (1 Work Package)
  • University College Cork       (1 Work Package) 

Q: How were the researchers (external) selected?
A: The researchers from outside the OPW were selected through a competitive tendering process whereby the tenders were advertised on either the website or the website of the Official Journal of the European Union (OJEU).
Q: When did the research begin and conclude?
A: The research aspects of the programme began in 2005 and concluded in 2011.
Q: How many surface water (hydrometric) gauging stations were used in the FSU research?
The original dataset used in the FSU research amounted to 215 hydrometric gauging stations, that possessed an overall total of 6,725 Annual Maximum flow values. For comparison, the Flood Studies Report (FSR) (NERC,1975) used just 112 hydrometric gauging stations from Ireland that possessed a total of 1,700 Annual Maximum flow values.
Q: How were the hydrometric gauging stations that were used in the analysis selected (criteria for use / basis for classification)?
A: The hydrometric gauging stations that were used in the FSU research were chosen to possess as a minimum, 10 years of Annual Maximum flow data. This group of stations was then subdivided into classifications of A1, A2, B, C. These classifications are described as follows:
  • A1 stations – Confirmed ratings good for flood flows well above QMED with the highest gauged flow greater than 1.3 times QMED and/or with a good confidence of extrapolation up to 2 times QMED, bankfull or, using suitable survey data, including flows across the flood plain.                                   
  • A2 stations – Ratings confirmed to measure QMED and up to around 1.3 times the flow above QMED. Would have at least one gauging to confirm and have a good confidence in the extrapolation.
  • B stations – Flows can be determined up to QMED with confidence. Some high flow gaugings must be around the QMED value.
  • C stations – Stations within the classification have the potential to be upgraded to B stations but require more extensive gauging and/or survey information to make it possible to rate the flows to at least QMED.

Those stations classified as 'C' were not used in the FSU research.

Q: What is the average length of record (in years) for the hydrometric gauging stations used?
A: The average length of record for the hydrometric gauging stations used in the FSU research was 31.3 years, this is in contrast to a figure of 15.2 years for the stations from Ireland that were used in the Flood Studies Report (FSR) (NERC, 1975).
Q: What is the breakdown by owner organisation of the hydrometric stations used?
A: The breakdown of the number of hydrometric gauging stations provided by the gauging authorities in Ireland is as follows:
  • OPW - 150
  • EPA (on behalf of Local Authorities) - 61
  • ESB - 4.
Q: How many rain gauging stations were used in the FSU research?
A: The Rainfall Depth-Duration-Frequency Analysis research of the FSU used a total of 577 daily rain gauging stations that possessed a total of 25,800 station years of data. This is in contrast to the Flood Studies Report (FSR) (NERC, 1975) which used 330 daily rain gauging stations from Ireland with a total of 3,300 station years of data. The analysis also used sub-daily rainfall data from 39 rain gauging stations, as opposed to just 12 that were used in the FSR.
Q: How were the rain gauging stations that were used in the analysis selected (criteria for use / basis for classification)?
A: The full set of rain gauging stations over the whole of the island of Ireland was used. However it was necessary to fill gaps in the records where necessary.
The Met Éireann archive for periods within 1941-2004 was used as this had already undergone extensive quality control. However, dry months and daily rainfalls in excess of 75.0mm were re-examined and some faulty data corrected before forming the initial table of daily rainfall. High-quality stations were picked out by examining the number of accumulated totals or missing days in each month of record. For these stations accumulations were broken up into daily values and missing days were estimated to give a complete set of daily values.
For most stations estimations were made by using up to six neighbouring stations with similar (within about 10%) average annual rainfall (AAR); these were ranked in order of preference and the first to have a complete record for a period requiring estimation was used as this had the perceived advantage of using a total actually recorded in the general area rather than a weighted mean.
If the AAR of the station requiring estimation differed considerably from its nearest neighbours then three neighbours with complete daily records were chosen and the global monthly ratios of target station over neighbour determined. For missing months the total was taken as a weighted mean of the three estimated totals and then reduced to daily values by reference to the daily rainfalls at the nearest neighbour.
Months with a total but no daily values were treated by forming the weighted mean of the three neighbours and giving it equal weight to the target station total; the agreement between the two was usually good. Again daily values were found from the estimated monthly total by reference to the nearest neighbour.
The remaining missing or accumulated days were treated by multiplying the daily values at the nearest available neighbour by the monthly ratio. Annual maxima extracted from the original and treated data showed that the differences were usually small as the quality of the chosen stations was high.
Q: What is the average length of record (in years) for the rain gauging stations used?
A: The average length of record for the daily rain gauging stations used in the FSU was 44.7 years. This is in contrast to the Flood Studies Report (FSR) (NERC, 1975) where the average record length for the Irish stations used was 10 years.
Q. What is the breakdown by owner organisation of the rain gauging stations used?
A: The daily rain gauging stations used in the rainfall Depth-Duration-Frequency Analysis were collected for both the Republic of Ireland and Northern Ireland. In the Republic of Ireland, Met Éireann provided data from 474 daily rain gauging stations and 31 sub-daily rain gauging stations.
In Northern Ireland, the UK Met Office and the Centre for Ecology and Hydrology (Wallingford) provided data from 103 daily rain gauging stations and 8 sub-daily rain gauging stations.
Q: The Flood Studies Report (FSR) (NERC, 1975) used rainfall inputs to derive design flood hydrographs. Why is rainfall not used in deriving design flood hydrographs in the FSU ?
A: At the outset of the FSU Programme it was decided not to re-use the Unit Hydrograph Method due to the scarcity of high resolution (hourly) rainfall data in Ireland. It was also decided that the steps in the process of inferring high resolution rainfall profiles to catchments that did not possess a high resolution rainfall station contained too many possible sources of error. In contrast, there was a wealth of continuous flow time series at river gauges in Ireland, and it was decided that statistical analysis of this data would produce superior methodologies for deriving design flow hydrographs.
Q: Why was the IBIDEM module included and what is its purpose?
A: At the stakeholder consultation workshops concerns were expressed about the absence of a link to rainfall data when constructing design flow hydrographs. As a result, the IBIDEM application was added in order to allow a comparison to be drawn between the FSR and FSU methods of hydrograph synthesis. IBIDEM allows the user to calculate the Time to Peak and the Standard Percentage Runoff that would be used in the FSR Unit Hydrograph method to produce a similar hydrograph to that produced by using the FSU methodologies.
Q: Will the FSU Research Reports be made available?
A: Yes, they are available to download from the Documents page of the FSU Web Portal
Q: Will hard copies of the FSU Research Reports, similar to FEH books, be available to the public?
A: There are currently no plans to publish hardcopies of the FSU  Research Reports. All of the information is available to download in pdf format from the FSU Web Portal.

3. About the FSU Portal 

Q: What is the FSU Web Portal?
A: The FSU Web Portal is the website of the FSU Programme. It is a free to use suite of online extreme rainfall and flood estimation tools. The main aim of the FSU Web Portal is to disseminate the methodologies, research and outputs from the FSU Programme to improve rainfall and flood estimation capabilities in Ireland.
Q: What are the main features of the FSU Web Portal?
A: The main features of the FSU Web Portal are as follows:
  • Homepage - User registration/login page and disclaimer
  • Site orientation map (SOM) tool
  • FSU database of rainfall and flood estimation data
  • Back-end interface
  • Data and software download module
  • Software applications for rainfall/flood estimation
  • Links to pdf documents / Third party websites / Objects / FSU Guidance Handbook (FGH)
  • Documents page containing FSU Research Reports (stored in pdf format)
  • On-screen Stepwise Guidance (OSG)
  • Audit trail reporting of key decisions made
  • Flood estimation reports - Print / export facility
  • Updateable News Page
  • Users Forum and Feedback Facility.
Q: Who was responsible for developing and implementing the FSU Web Portal?
A: The FSU Web Portal was developed by a consortium of RPS Group and HydroLogic BV (the Netherlands). The delivery of the Portal was managed by the OPW and the FSU Web Portal Steering Group.
Q: How were the developers of the FSU Web Portal selected?
A: The developers of the FSU Web Portal were selected after a competitive tender process. In July 2012, the Request for Tenders (RFT) for the 'Provision of Services for the Development of a Web-based Applications Portal for the FSU' was advertised on the websites of the Official Journal of the European Union (OJEU) and on eTenders. Tender Submissions were received in September 2012 and all of those who tendered were notified of the contract award decision in November 2012.

Q: When did development of the FSU Web Portal begin and conclude?
A: Development of the FSU Web Portal began in December 2012. The FSU Web Portal was launched in June 2014.
Q: For what level of user has the FSU Web Portal been designed?
A: The FSU Web Portal has been designed and developed for use by competent hydrologists and meteorologists who are familiar with hydrological and meteorological techniques. The FSU is not intended to be used by those who have no background in hydrological or meteorological analysis.

Q: Will training be provided to users of the FSU Web Portal?
A: Training will be provided on the use of the FSU Web Portal in the second half of 2014. It is expected that this training will take place in the larger urban centres of Dublin, Cork, Galway and for geographical reasons a further venue in the midlands will also be chosen. Those who have not received training in the use of the FSU Web Portal will be provided with a number of features within the Portal that will assist them at each step of the calculation process. At each step, the user can click on the 'help' buttons provided in order the access the On-Screen Stepwise Guidance (OSG). The OSG will present information on what inputs are required for that particular step in the calculation, and will also contain a link to the relevant section of the Technical Research Report Volumes should the user require more detailed information. Users may also refer to the FSU Guidance Handbook (FGH). This is effectively the Users Manual' for the FSU Web Portal, and may be downloaded from the Documents page of the Portal.
Q: Will the FSU Web Portal be maintained and kept up-to-date?
A: The FSU Web Portal was designed such that the day-to-day maintenance of the Portal can be carried out by OPW staff through using a back-end interface. It is expected that minor updates will occur at two month intervals typically. These minor updates will be limited to items such as uploading new research reports/documents and updating the News Page. It is expected that major updates to the Portal will take place at two to three year intervals typically. These major updates will be deemed necessary if there are any major changes in FSU data or methodologies.
Q: Why is there an audit trail facility on the FSU Web Portal?
A: The Audit Trail facility on the FSU Web Portal is used to record the decisions made by users, and the outputs generated from the FSU Web Portal during their rainfall or flood calculation. This information is then used to produce a Flood Estimation Report that can be submitted as part of a Professional Report, e.g. for Section 50 consent applications, planning applications or similar uses.
The Audit Trail Reports will also be used by the FSU Helpdesk Team to examine user needs and behaviour, and will ultimately guide the process of improving the FSU Web Portal so as to benefit the end user.
Q: Are users required to use the FSU Web Portal for flood and rainfall estimation?
A: Whilst the FSU methodologies and Web Portal will be the preferred methodology for flood and rainfall estimation in Ireland over the coming years, it is not mandatory that the FSU methodologies and Web Portal be used.
Q: Can users reproduce FSU datasets (e.g. use PCDs and spatial data) from the FSU Web Portal?
A: Yes, the FSU datasets are all available from the FSU Web Portal via the Data & Software download module. Re-use of these FSU datasets from the website is subject to licence under DIRECTIVE 2003/98/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on the re-use of public sector information. Full details of this licence can be found at
Q. How was the FSU Web Portal tested prior to launching?
A: The FSU Web Portal was tested in two separate stages. The first stage was Alpha Testing, which involved testing of the FSU Web Portal by the developers and by a selected group made up of consultants, third level institutions, OPW staff and other state organisations involved in hydrology related matters. The Alpha Testing, carried out in October 2013, focused on the general functionalities of the Portal.
Beta Testing of the FSU Web Portal was carried out by a selected group of testers between December 2013 and January 2014. This involved detailed testing of the functionalities of the FSU Web Portal and also of the flood estimation calculations of the Portal.

4. About the FSU Methodologies

Q: What are Physical Catchment Descriptors (PCDs)?
A: Physical Catchment Descriptors represent specific characteristics of a catchment that are quoted as numerical values. They are usually given in one of three forms: actual measured units, proportions, or indices. Examples of each of these types are as follows:
AREA - Surface water catchment area (an actual measured unit quoted in km2)
FOREST - Proportion of Forest Cover in a catchment (quoted as a proportion between 0 and 1)
BFIsoil - Baseflow Index derived from soil data  (quoted as an index between 0 and 1).
Q: Is there a quick guide / glossary for each Physical Catchment Descriptor (PCD)?
A: The content of TRR Volume IV provides a summary description of all of the Physical Catchment Descriptors used in the FSU research.
Q: What datasets were used for the FSU Physical Catchment Descriptors (PCDs)?
A: The datasets that were used for the FSU Physical Catchment Descriptors (PCDs) were collected from a number of different sources. The base data was then manipulated to provide PCD values for each gauged and ungauged river location on the Blueline River Network. The following is a list of the catchment descriptors and the source of the base data that was used to derive them:

Physical Catchment Descriptor (PCD) Abbreviated Name Source of Base Data
Network Length NETLEN Blueline River Network
Stream Frequency STMFRQ Blueline River Network
Drainage Density DRAIND Blueline River Network
Mainstream Length MSL Blueline River Network
Mainstream Slope S1085 Blueline River Network and the OSi DTM
Taylor Schwarz Slope TAYSLO Blueline River Network and the OSi DTM
Index of Arterial Drainage ARTDRAIN Blueline River Network and OPW Drainage Scheme Maps
Index of Arterial Drainage 2 ARTDRAIN2 Blueline River Network and OPW Drainage Scheme Maps
Catchment Area AREA OSi DTM
Catchment Centroid Easting CENTE OSi DTM
Catchment Centroid Northing CENTN OSi DTM
Minimum Catchment Elevation ALTMIN OSi DTM
Mean Catchment Elevation ALTBAR OSi DTM
Maximum Catchment Elevation ALTMAX OSi DTM
Catchment Elevation Range ALTRANGE OSi DTM
Standard Deviation of Catchment Elevations ALTSTD OSi DTM
Standard Period Average Annual Rainfall SAAR Met Éireann
Standard Period Average Annual Potential Evapotranspiration SAAPE Met Éireann
Flood Attenuation by Reservoirs and Lakes FARL Blueline River Network and the OSi DTM
Index of Urban Extent URBEXT Corine Landcover Dataset
Proportion of Forest Cover FOREST Coillte Forestry Database, Corine Landcover Dataset, and the Forestry Inventory Parcel System
Proportion of Peat Cover PEAT Corine Landcover Dataset
Proportion of Grassland/Pasture/Agriculture PASTURE Corine Landcover Dataset
Proportion of Extent of Floodplain Alluvial Deposit ALLUV Teagasc/EPA Soil Parent Materials mapping
Index of Typical Catchment Wetness FLATWET FSU Work Package 5.4
Aquifer Class Statistics Aquifers GSI Groundwater Protection Schemes
Soil Class Statistics Soils Teagasc National Soils Dataset
Subsoil Permeability Class Statistics Subsoils GSI National Subsoil Permeability Dataset
Flood Attenuation Index FAI FSU Work Package 5.3

Q: How were the FSU equations derived?
A: The primary means of deriving the FSU equations was through regression analysis applied to the Physical Catchment Descriptors (PCDs) that describe the physical characteristics of a catchment.
Q: What is the uncertainty associated with the flood estimation equations?
A: The uncertainty associated with the equation for the estimation of the index flood (QMED) is expressed in terms of 68% and 95% confidence intervals. These confidence intervals are calculated from the Factorial Standard Error (FSE) associated with the 7-variable QMED equation, which is 1.37.  The 68% confidence intervals are in the range (QMED*1.37, QMED/1.37), or in other words in the range (1.37*QMED, 0.73*QMED). The 95% confidence intervals are in the range (QMED*1.372, QMED/1.372), or in other words in the range (1.88*QMED, 0.53*QMED).
Q: What is the uncertainty associated with the rainfall (DDF) estimation equations?
A: Refer to Chapter 4 and Appendix C of Met Éireann's Technical Note 61, which can be found on the Documents page of the FSU Web Portal.
Q: What is the difference between fixed and sliding for rainfall duration  type?
A: The data provided by Met Éireann for the rainfall Depth-Duration-Frequency Analysis comprised both hourly and daily rainfall measurements. Much of the analysis of rainfall data used the daily rainfall totals at each rain gauging station. These rainfalls are measured at fixed intervals of one day at 09:00am. In some cases, large rainfall events may span two days of  these fixed durations. Therefore the concept of a sliding duration is introduced to allow users to estimate that total rainfall over any 24 hour period.

Q: How reliable is the result from the flood growth curve analysis?
A: The reliability of the flood growth curve analysis stage of the FSU method is given in terms of standard error. Depending on the statistical distribution used to fit the growth curve and the target return period the possible errors associated with the growth curves are given in the table below:

T Se(XT)%,EV1 Se(XT)%,GEV
5 0.7  to  0.8 0.8   to  1.0
10 1.1  to  1.2 1.4   to  1.8
25 1.4  to  1.6 2.3   to  3.0
50 1.6  to  1.8 3.0   to  3.9
100 1.8  to  2.0 3.7   to  5.0
500 2.1  to  2.3 5.4   to  7.3

The standard errors quoted in the table above are for the EV1 and the GEV distributions. It is reasonable to adopt the same values of standard errors as the EV1 distribution for the LN2 and the LO distributions. Furthermore it is reasonable to adopt the same standard errors as the GEV distribution for the LN3 and GLO distributions.
Q: Should Euclidean or Geographical Pooling Schemes be used for Pooling Group Analysis?
A: The default pooling scheme in the FSU is the Euclidean Pooling scheme, and should be used in preference to the Geographical Pooling scheme.

Q: What distribution(s) should be used for the flood growth curve analysis?
A: In general the two-parameter distributions EV1 and LN2 should be used at gauged locations, whereas the three-parameter distributions GEV and GLO should be used at ungauged locations. Users should use their own judgement when choosing between each of these. Visual aids (L-Moment Ratio Diagrams) that are provided in the FSU Web Portal may be used to assist in the decision making process.
Q: Is there a limit to the catchment size to which the FSU methods for ungauged sites can be applied?
A:  The FSU methods can be used with confidence for catchments with areas between 25km2 and 10,000km2. Further research conducted under the FSU on a limited number of small catchments indicates that the FSU may also be used, with caution, for catchments with an area between 5km2 and 25km2 .  However for catchments with area less than 5km2, the FSU is not deemed applicable and users should examine a number of alternative methods.
Q: How do the FSU methodologies apply in relation to controlled flows (weirs, dam, etc.)?
A: The FSU methodologies are not intended for use on controlled channels such as those downstream of a dam or sluice gates. The flow in such channels are not considered to exhibit 'natural' flow characteristics and are therefore outside the range of application of the FSU.
Q: How do you generate a Design Rainfall Table?
A: There is currently no facility within the FSU Web Portal for producing a Design Rainfall Table. There are plans to include this in the next version of the FSU Web Portal.

5. General Questions

Q: What is the Flood Studies Report (FSR)?
A: The Flood Studies Report (FSR) was published in March 1975, and was based on extensive research and analysis of available hydrometric and rainfall records in Ireland and the United Kingdom (UK) up to and including 1970. It consisted of five volumes that covered hydrological, meteorological, and flood routing studies as well as a volume containing the data used and a volume of maps for applying the results derived from the analyses. The flood frequency studies volume of the FSR used some 1,700 record years of data from a total of 112 hydrometric gauging stations from around Ireland. The meteorological studies used data for the decade 1961-1970 from 330 daily and 12 sub daily rain gauges and was subjected to depth-duration-frequency analysis.
The work on the Flood Studies Report was guided by an interdepartmental Steering Committee and lasted almost five years. Its primary objectives were: (i) To provide a means of estimating the Flow Vs Return Period (Q-T) relationship for flood peaks at gauged or ungauged locations, (ii) to provide a means of estimating the flood hydrograph of given peak return period for use in circumstances where flood volumes and storage attenuation are involved, e.g. for routing through reservoir or channel storage, and (iii) to provide rainfall depth-duration-frequency relationships over any area to enable estimates of storm depths and profiles for all return periods within the range of all possible rainfalls to be made.
The FSR generally relied on ‘no data’ methods that were developed based on the relatively short record of data up to 1970. In the years that followed, further updates to the FSR methodologies were issued between 1977 and 1988 through a total of 18 Flood Studies Supplementary Reports (FSSRs).
Q: How is the FSU an improvement on the FSR?
A: The most notable improvement between the Flood Studies Report (FSR) (NERC, 1975) and the FSU is that the FSU utilises over 30 years more rainfall and flow data. The FSU data is also more contemporary than its 1975 counterpart, and would be thought to account for any effect of climate change since the mid 1970's.
Advances in computing power since the publication of the FSR have allowed more complex analyses of the data, and hence new methodologies have been formulated for calculating the index flood (QMED), flood growth factors, and the synthesis of design hydrographs at ungauged locations. The factorial standard error for the estimation of the index flood for the FSU is 1.37, in contrast to a value of 1.5 that is quoted for the FSR. The calibration of the method for Synthesising Hydrographs under the FSU is based on data from 90 hydrometric gauging stations, whereas the FSR used none.
Improvements in Information Technology and the advent of the Internet now allows the dissemination of the FSU research to be web-based as opposed to paper based. The dissemination of the FSU methodologies via the internet will also allow for seamless updating of the FSU methodologies in the future, thus negating the need to publish and distribute supplementary reports.

Q. What are the main differences between the FSU and the FSR?
A: The main differences between the FSU and the Flood Studies Report (FSR) (NERC, 1975) are as follows:
  1. There was substantially more data available for the FSU research.
  2. The FSU suite of methodologies are specific to Irish conditions, whereas the FSR covered both Ireland and the UK.
  3. Online direct calculation of rainfall Depth-Duration-Frequency relationships. It is no longer necessary to calculate the Index rainfall (M5-2day rainfall) as an intermediate step.
  4. Abandonment of the Unit Hydrograph method in favour of a statistical  hydrograph method.
  5. Instead of a single flood growth curve for the whole of Ireland (FSR), the FSU allows the calculation of separate growth factors at any location in Ireland.
  6. Under the FSU, Physical Catchment Descriptors (PCDs) have been prepared for all locations in Ireland, whereas in the FSR it was necessary for the user to extract the PCDs from paper maps.
  7. Web-based dissemination as opposed to paper-based dissemination.

Q: What is the Flood Estimation Handbook (FEH)?
A: Due to the large number of updates to the Flood Studies Report (FSR) (NERC, 1975) methods that were issued between 1977 and 1988 (18 Flood Studies Supplementary Reports), it became clear that many practitioners were using differing versions of the FSSR methodologies, which led to the need to once again standardise practices. Indeed a considerable database of rainfall and flow measurements had also amassed in the years since the publication of the FSR and this was also one of the factors driving the update of the flood estimation techniques to be used in the UK. The publication of the UK Flood Estimation Handbook (FEH, Institute of Hydrology, 1999) provided this long awaited standardisation.
It gives guidance on rainfall and river flood frequency estimation in the UK and provides methods for assessing the rarity of notable rainfalls or floods. The FEH was issued in a set of five printed volumes covering: rainfall frequency estimation, statistical procedures for flood frequency estimation, restatement and application of the FSR rainfall runoff method and a description of catchment descriptors. Its coverage does not extend to the Republic of Ireland.
Q: What are the main differences between the FSU and the FEH?
A: The main differences between the FSU and the FEH (Institute of Hydrology, 1999)  are as follows:
  1. The FSU is specific to Irish conditions, whereas the FEH is specific to the UK.
  2. The FSU uses a statistical hydrograph method whereas the FEH uses the re-vitalised flood hydrograph model to synthesise flood hydrographs at ungauged locations.
  3. The FSU uses different Physical Catchment Descriptors to those used in the FEH.
  4. The FSU uses a web-based dissemination whereas the FEH is based on a set of published volumes accompanied by a CD-ROM that contains data and software.
Q: Were data from the extreme floods in November 2009 and winter 2015/2016 used in the FSU research and analysis?
A: Data from the November 2009 and winter 2015/2016 floods in Ireland have not been incorporated into the current version of the FSU Web Portal. The decision was made by the FSU Management Team to proceed to provide a working version of the FSU Web Portal first, before addressing the issue of updating the data behind the FSU methodologies. It is expected that data from the 2009 and 2015/2016 floods will be incorporated into the next update of the FSU methodologies. 
Q: What is the effect of not having included the November 2009 and winter 2015/2016 flood data?
A: As the FSU methodologies use the median of the Annual Maximum flood series it is expected that the effect of not including the 2009 and the winter 2015/2016 floods will be negligible.
Q: How did the FSU Programme deal with the issue of climate change / effects of global warming?
A: The FSU methodologies have deliberately not included guidance on climate change. It was decided not to do so because the recommendations for climate change are still uncertain and are liable to vary from year to year as new research becomes available. In this regard, users are advised to contact the OPW to ascertain what are the most current recommendations on adjustments to include for climate change.
Q: What happens if the FSU methodologies are updated, e.g. will the calculations carried out two years ago become invalid / incorrect?
A: When a user carries out a rainfall or flood estimation using the FSU methodologies, the date of the estimation is recorded. Any outputs from that time are deemed to be based on the best available data/methodologies 'at that time'. Where further updates are made to the FSU methodologies, these will not cause calculations carried out before the update to be deemed as incorrect.

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