TopNet

Purpose

The hydrological model TopNet was developed at NIWA and is commonly used in New Zealand. Typical applications include flood forecasting, irrigation planning and estimates of climate change impacts on river flows.

Description

TopNet is a semi-distributed hydrological model for simulating catchment water balance and river flow.

TopNet uses a modelling approach which combines an understanding of hydrology and soil science to calculate the water available in various locations (soil, lakes, streams) over time. In simple terms, TopNet is a catchment water-balance calculator.

Using this computer-based model scenarios can be tested based on specific ‘variables’, such as size of reservoir, amount and timing of rainfall, size of the catchment, amount and timing of irrigation, and so forth. TopNet allows calculation of how these variables will interact over time. TopNet has resulted in the following:

• New Zealand’s first national-scale water resources simulation model
• The most detailed national-scale water resources map ever produced
• The ability to estimate river flows in all ungauged catchments in New Zealand

Latest Version	Version 11 (2011)
State of Development	Stable Release
Current Development Activity	Coupling with a glacier component and developing a retrospective streamflow assimilation scheme.

Scope

Outcome Areas	Environmental
Management Domains	Land
Subdomains	Water Yield
Intended End Users	Highly trained personnel / In-house specialist
Spatial Extents	Local (i.e. Catchment or District), Regional, National
Spatial Dimensions	2D
Temporal Resolutions	Hours
Temporal Extents	Decades
Steady State or Dynamic	Dynamic
Level of Integration	Environmental

Input & Output Data

Key Input Data	Land Use, Land Cover, Rainfall, Temperature, Potential Evaporation Topography, soils
Input Data Formats	netcfd
Key Output Data	Runoff, Drainage Soil moisture, snow
Output Data Formats	netcdf

Accessibility

Open/Closed Source	Closed Source

User Information

Operating Systems	MS Windows, Linux
Software Needed	netcdf libraries
User Interface	Other (please specify) Command Line
Ease of Use	Difficult There is a significant training overhead to learn to use Topnet. Specific implementations customised for users are much simpler to operate, and more limited in functionality.
Use in Policy Process	Plan (Policy Formulation)
Documentation	User manual and help files available on the NIWA website (https://one.niwa.co.nz/display/HYPRO/TOPNET+++Model).
Support	On research collaboration basis
Users Forum	None

Technical Considerations

Programming Language	Fortran and C
Methods included for calibration and validation	(1) Manual calibration (2) NLFit: a parameter fitting Windows-based program that uses optimal parameter search algorithms.
Methods included for managing uncertainty	Monte Carlo simulation: a large number of different parameter sets are tried and the best set selected based on an objective function (e.g. the Nash Sutcliffe criteria).
Keywords	flooding, irrigation, climate change, rivers, flow
Key References	Clark, M.P.; Woods, R.A.; Zheng, X.; Ibbitt, R.P.; Slater, A.G.; Rupp, D.E.; Schmidt, J.; Uddstrom, M.J. 2008:. Hydrological data assimilation with the Ensemble Kalman Filter: use of streamflow observations to update states in a distributed hydrological model. Advances in Water Resources: 31, 1309-1324.

Associated Case Studies