Catchment Tools Project

CatchmentTools Project: catchment characterisation and evaluation of programme of measures

Funded by Environmental Protection Agency’s Research Programme (2014 – 2016)


The ‘Catchment Management Support Tools for Characterisation and Evaluation of Programme of Measures’ project, or CatchmentTools Project, developed data analysis tools and models for assessing nutrients in Irish catchments. These models build on the work of the STRIVE Pathways Project, and are used to support catchment management by assisting catchment scientists and managers to:

  • Characterise the catchment: identify risks of pollution sources and areas of susceptibility. Characterisation includes understanding;
    • the physical/natural catchment,
    • the anthropogenic impacts &
    • water use in a catchment.
  • Implement Programmes of Measures (PoMs): understanding the sources, pathways and receptors can be used to target monitoring and PoMs to improve or maintain WFD water body status.

The Catchment Characterisation Tool (CCT), Source Load Apportionment Model (SLAM) and Catchment Modelling Tool (CMT) are models for assessing the movement of nitrogen and phosphorus in catchments. These tools help scientists and managers to visualise and understand the Source-Pathway-Receptor relationships in different but complementary ways. The modelling approach aims to provide applied research in the form of a user-friendly model results with map outputs.


Mockler, E.M., Deakin, J., Archbold, M., Daly, D. & Bruen, M. (2016) Nutrient Load Apportionment to Support the Identification of Appropriate Water Framework Directive Measures. Biology and Environment 116B(3) 245-263.

Gill, L.W. & Mockler, E.M. (2016) Modeling the pathways and attenuation of nutrients from domestic wastewater treatment systems at a catchment scale. Environmental Modelling & Software 84 363-377.

Ní Longphuirt, S., Mockler, E.M., O’Boyle, S., Wynne, C. & Stengel, D.B., (2016) Linking changes in nutrient load source apportionment to estuarine responses: An Irish perspective. Biology and Environment 116B(3) 295-311.

Zimmermann, J., Fealy, R., Lydon, K., Mockler, E.M., O’Brien, P., Packham, I., Smith, G. & Green, S. (2016) The Irish Land-Parcels Identification System (LPIS) – Experiences in on-going and recent environmental research and land cover mapping. Biology and Environment: Proceedings of the Royal Irish Academy 116B(1) 1-10.

O’Boyle, S., Quinn, R., Dunne, N., Mockler, E.M. & Ní Longphuirt, S. (2016) What have we learned from over two decades of monitoring riverine nutrient inputs to Ireland’s marine environment? Biology and Environment 116B(3) 313-327.

Catchment Nutrient Models

CCT : Agricultural Nutrient Pollution Impact Potential Maps

Description: The CCT estimates long-term annual average losses of N and P from diffuse agricultural sources using export coefficients based on GIS maps for both the surface and groundwater pathways.

Purpose: To assess spatial variations in diffuse nutrient pollution from agricultural sources.

Output:   Pollutant Impact Potential maps showing Critical Source Areas for nitrate & phosphate in:

    1. The subsurface / groundwater receptor
    2. The near surface pathway (all non-groundwater paths)
    3. The local surface water receptor (1 + 2)

SLAM : Nutrient Source Loading Apportionment Model

Description: SLAM is a source-oriented model that predicts the N & P exported from each sector in a catchment using GIS, including the CCT, and monitoring data where available.

Purpose: To rank the sources (e.g. pasture, WWTP) contributing to nutrient loads in a catchment.

Output:   Maps & charts showing proportion of nutrients attributed to each sector.

CMT : Dynamics of Flow Paths & Nutrient Processes

Description: The CMT is a dynamic model currently in development for tracking the short-term variation in nutrient quantities and relationships with time-varying drivers. The CMT is suitable for research studies and detailed assessments in catchments that require:

  • Seasonal assessment of critical pollutants and pathways
  • Analysis of the hydrological connectivity between sub-basins to predict varying pollution & dilution effects
  • Assessment of direct discharges to rivers including in-stream processes
  • Nutrient load source apportionment to determine risk ranking of sources at high and low flows

Purpose: To assess short and long term dynamics of flows and concentrations.

Output:   Maps & time-series showing concentrations of nutrients attributed to each flow path.


 Table 1. Summary of model structures and outputs.

Name Catchment Characterisation Tool Source Load Apportionment Model Catchment Modelling Tool
Type Spatial GIS model Data driven GIS model Semi-distributed hydrological (SMART) & nutrient model
Time-step Average annual Annual (capacity for seasonal/ low flow) Daily or sub-daily
Nutrient Sources Average annual diffuse and small-point All nutrient sources Diffuse, small-point & large point (daily/ monthly/ seasonal)
Pathways: Hydrology 2 : near surface and sub-surface;limited hydrological connectivity As defined by methods for each sector- includes CCT for diffuse agri 4 : overland, interflow, shallow and deep groundwater + in-stream processes
Pathways: Nutrients Export coefficients from literature and expert opinion. Export coefficients – dependant on method for each sector Mass balance equations, currently following INCA N & P models.
Receptors Groundwater and ‘local’ surface water Downstream lake/ river water body / estuary Downstream lake/river water body
Output Average annual map output showing variation of Pollutant Impact Potential for N & P within a sub-catchment. Map output and tables of results showing estimated nutrient load exported from each sector for each sub-catchment. Flow path simulations & hydrological connections for high & low flow / seasonal variations between sub-catchments for flows, N & P and sediment.


Source-Pathway-Receptor (S-P-R) concept

The Source-Pathway-Receptor (S-P-R) concept is commonly used to describe the transport and attenuation of contaminants through our environment, and was the basis for the development of the two models of the CMST (Table 1). Critical Source Areas (CSAs) are locations where a relatively high proportion of the total pollution exported from the catchment originates (Pionke et al., 2000; White et al., 2009). They occur when a significant amount of contaminant available for mobilisation (Source) coincides with a transport mechanism (Pathway) to a receiving water body of interest (Receptor). Their identification is a key tool for environmental managers using a risk-based approach to decision making. Figure 1 illustrates some potential sources, pathways and receptors in a typical agricultural catchment.

Figure 1. Sources, pathways & receptors in an agricultural catchment



Pionke, H. B., W. J. Gburek and A. N. Sharpley (2000). “Critical source area controls on water quality in an agricultural watershed located in the Chesapeake Basin.” Ecological Engineering 14(4): 325-335.

White, M. J., D. E. Storm, P. R. Busteed, S. H. Stoodley and S. J. Phillips (2009). “Evaluating Nonpoint Source Critical Source Area Contributions at the Watershed Scale.” Journal of Environmental Quality 38(4): 1654-1663.