Rotorua Taupo Nitrogen Model (ROTAN-Annual)

Purpose

ROTAN-Annual is used for the prediction of nitrate inputs to lakes for various land use, rainfall, and mitigation scenarios to inform land use policy and decision making for improving environmental outcomes.

Description

ROTAN is a daily/weekly time-step, GIS-based, rainfall-runoff-groundwater model which can predict the water flows and nitrogen concentrations in streams in daily or weekly time steps. Used at a catchment scale, it can be used to predict nitrogen loads to lakes. It can take account of time lags between nitrogen leaching, and its arrival at the lake.

The initial version of ROTAN (ROTAN-2011) was developed to model nitrogen in Lakes Rotorua and Taupo. It is a GIS-based catchment hydrology and water quality model that models the effects of land-use change and nitrogen mitigation measures such as riparian margins and plant uptake on nitrogen export to waterways. This initial model is based on the Scandanavian HBV and HBV-N models in which soils and aquifers are modelled as a series of fully-mixed reservoirs (buckets) connected in series and parallel.

The ROTAN-2011 model (Rutherford et al. 2008, 2009, and 2011) has been used to predict the effects of land use changes on nitrogen loads delivered to Lake Rotorua in surface and groundwater.  The original ROTAN-2011 model relied on OVERSEER v5 to estimate nitrogen losses from farmland. That version of OVERSEER is no longer supported and was replaced by OVERSEER v6. Therefore ROTAN-2011 needed to be re-calibrated before it could be used with OVERSEER v6.

This necessitated the redevelopment of ROTAN-2011. University of Waikato is reprogramming a new version (ROTAN-V2). However, in the interim NIWA was commissioned by BoPRC in March 2016 to develop a simplified
version (ROTAN-Annual) and calibrate it using:

• OVERSEER v6 nitrogen losses
• recent stream monitoring data
• revised groundwater boundaries, and
• updated land use information.

ROTAN-Annual is providing technical support to BoPRC and stakeholders during the plan change process for Lake Rotorua Catchment. ROTAN-Annual builds on modelling work undertaken in Hawke’s Bay during 2010-2011 (Rutherford 2013). This was undertaken to support the TRIM-Catchment model which was developed as a component of the TRIM (Tukituki River Model) nutrient-periphyton model. The concepts of TRIM-Catchment were further developed and the model re-coded to produce ROTAN-Annual.

ROTAN-Annual routes nitrogen through the catchment using mass flux which is consistent with OVERSEER which estimates annual nitrogen losses. Attenuation coefficients are calibrated using annual average stream concentrations (flux/flow).

In the model nitrogen travels to the lake by three pathways: ‘quickflow’ and ‘streamflow’ (that reach the lake within a year), and ‘slowflow’ (groundwater that may take decades to reach the lake). Nitrogen ‘loss’ along each pathway is quantified using separate attenuation coefficients.

ROTAN offers a range of outputs, including:

• maps of flow and nutrient delivery pathways from each part of the catchment to the lake
• tables for each part of the catchment, showing quantities of flow and nutrients, time delays and nutrient losses
• tables and graphs showing historic trends in land use, stocking rate and fertiliser usage
• tables and graphs showing the relationship between historic trends in land use, rainfall and stream nutrient concentration
• predictions of nutrient inputs to lakes under various land use, rainfall and mitigation scenarios.

ROTAN-Annual is a closed source/use tool and is only intended to be available to NIWA research team.

State of Development	Closed Beta
Current Development Activity	Nil

Scope

Outcome Areas	Environmental
Management Domains	Freshwater
Intended End Users	Researcher Waikato University
Spatial Resolutions	500-1000m
Spatial Extents	Local (i.e. Catchment or District)
Spatial Dimensions	3D
Temporal Resolutions	Days
Temporal Extents	Days, Months
Steady State or Dynamic	Dynamic
Level of Integration	Environmental

Input & Output Data

Key Input Data	Land Use, Rainfall, Land Cover, Potential Evaporation
Input Data Formats	GIS compatible files
Key Output Data	Runoff, Drainage water flows and nitrogen concentrations
Output Data Formats	GIS Compatible Files

Accessibility

Open/Closed Source	Closed Source
Licence Type	Unknown
Licence Cost (Non Commercial)	Not available for non-commercial use
Licence Cost (Commercial)	Not available for commercial use

User Information

Operating Systems	MS Windows ArcGIS
Software Needed	ArcGIS ArcGIS
User Interface	Graphical desktop
Ease of Use	Difficult Not intended for use outside the NIWA research group that developed it. Little work done on user manuals, help screens, or internal checking.
Use in Policy Process	Plan (Policy Formulation), Review (Issue Identification)
Documentation	Rucinski, D., S. Wadhwa, J. C. Rutherford. (2006). ROTAN - ROtorua and TAupo Nitrate Model. User's Guide. Hamilton, NIWA.
Support	None outside NIWA
Users Forum	None outside NIWA

Technical Considerations

Programming Language	ESRI Visual Basic
Methods included for calibration and validation	Calibrated by fitting to measured flows and nitrogen concentrations in streams, and to published annual nitrogen loads entering the lake.
Methods included for managing uncertainty	Goodness of fit quantified (RMS error)
Analytical Techniques	GIS
Model Structure	Based on the Scandanavian HBV and HBV-N models. Soils and aquifers are modelled as a series of fully-mixed reservoirs (buckets) connected in series and parallel.
Keywords	Nitrogen, Land use, Lake, eutrophication
Linkages to other Models	Dynamic Reservoir Simulation Model - Computational Aquatic Ecosystem Dynamics Model (DYRESM- CAEDYM) OVERSEER® Scenario Planning
Key References	Rutherford, J. C. (2016). Predicting nitrogen loads to Lake Rotorua using the ROTAN-Annual. Napier. NIWA Client Report 2016102HN. Rutherford, J.C. (2013) Effects of land use on nutrients. Phase 2 studies in the Tukituki River, Hawke’s Bay. NIWA Client Report HAM2013-025. Hamilton. Rutherford, J. C., C. C. Palliser, et al. (2011). Prediction of nitrogen loads to Lake Rotorua using the ROTAN model. Hamilton, NIWA: NIWA Client Report HAM2010-134. 178. Rutherford, J. C., C. C. Palliser, et al. (2009). Nitrogen exports from the Rotorua catchment - calibration of the ROTAN model. NIWA Client Report HAM2009-019, NIWA, Hamilton: 62. Rutherford, J.C., Tait, A., Palliser, C.C., Wadhwa, S., Rucinski, D. (2008) Water balance modelling in the Lake Rotorua catchment. NIWA Client Report HAM2008-048. Hamilton.

Associated Case Studies