ISIS Technical Review

"a flexible and comprehensive range of tools for designing cost-effective engineering schemes and developing catchment strategies"

ISIS Flow / Hydrology

ISIS Flow is a full hydrodynamic simulator for modeling flows and levels in open channels and estuaries and is at the heart of the system. ISIS Flow is able to model complex looped and branched networks, and is designed to provide a comprehensive range of methods for simulating flood plain flows. ISIS Flow incorporates both unsteady and steady flow solvers, with options that include simple backwaters, flow routing and full unsteady simulation. The simulation engine provides a direct steady-state solver and adaptive time-stepping methods to optimise run-time and enhance model stability.

ISIS provides full interactive views of the model data and results using plan views, long sections, form based editing tools and time series plots. Results can also be reported in text and tabular formats. The software includes a wide range of diagnostic error checks and a comprehensive on-line help system.

Simulation of hydraulic structures

A key strength of ISIS Flow is the ability to model a wide range of hydraulic structures including all common types of bridges, sluices, culverts, pumps and weirs. Where ever possible, standard equations or methods are incorporated into the software so that the calculation of level and discharge relationships is fully handled by the software. For structures with automatic operation such as pumps and sluices ISIS Flow allows the user to incorporate logical control rules.

Advanced backwater solutions

A backwater solution is all that is needed for many river engineering applications. ISIS Flow incorporates a powerful steady state solver, providing engineers with an easy to use tool for day to day application in engineering design. Although easy to apply to simple systems, the steady state solver includes the full range of hydraulic structures and is able to model complex looped channels and trans-critical flows in steep rivers. This arguably gives ISIS a greater range of application than any other steady state modeling software. The modular design of ISIS allows any model constructed for backwater modeling to be used for unsteady simulation if an unsteady solution is subsequently required.

Rainfall-runoff modeling

Provided with ISIS Flow is an event-based hydrological module. For UK use, the well established Flood Studies Report (FSR) unit hydrograph method is available, including the recommendations of FSSR 16. In the near future this will be enhanced with the methods of the new Flood Estimation Handbook (FEH). For other countries the US Soil Conservation Service (USSCS) method is available. Regardless of the method used, the software allows the user to specify observed or predicted rainfall profiles and unit-hydrographs.

ISIS Quality

ISIS Quality is a fully featured water quality simulator, and includes advection / diffusion of conservative and decaying pollutants, water temperature, sediment transport, interaction of quality determinands with sediments, phytoplankton and pH. The water quality engine can be used in conjunction with a full hydrodynamic simulation to simulate water quality processes in detail, or can be driven by simpler flow routing methods for less detailed applications. The user is able to specify the processes included in the simulation, providing focus on the specific needs of the particular study and improved productivity.

ISIS PDM

The PDM (Probability Distributed Moisture) model is a general-purpose, lumped conceptual model developed and maintained by the UK Institute of Hydrology. The software provides a highly effective representation of the runoff generation process and has been specifically designed to work with long records of flow and rainfall.

ISIS PDM is a licensed development of the PDM model, providing conceptual hydrology support within ISIS. ISIS PDM consists of a stand-alone model setup and calibration tool, and a new ISIS Flow boundary condition for generating model inflows from a calibrated PDM model.

The PDM model derives its name from the representation of soil-moisture storage, as the variation of storage capacity across a catchment is described by a probability distribution. Direct runoff from the saturated area of the catchment passes into surface storage whilst the groundwater recharge from the soil moisture store passes into groundwater storage. The outflows from both stores form the total model output at the catchment outlet.

A key feature of ISIS PDM is a model calibration environment that allows for both interactive "manual" parameter estimation and automatic optimisation of individual or multiple model parameters. The user is able to see immediately the effect of modifying any model parameter, through both graphical views and statistical indices. The model parameters can also be estimated automatically using a simplex optimisation procedure and in this case the user has complete control over which parameters are optimised and the final parameters selected.

ISIS Sediment

ISIS Sediment is the mobile bed sediment transport module used with ISIS Flow for studying the morphology of rivers and alluvial canals. It has been applied to engineering problems and for studying sedimentation problems in rivers and canals, including a number of the worlds major irrigation systems. The software predicts sediment transport rates, changes in bed elevation and amounts of erosion and deposition throughout the channel system. A range of sediment transport predictors are included and additional formulae are easily incorporated. The conveyance properties of the river sections are updated throughout the simulation based on the predictions of the module. ISIS Sediment also includes the ability to simulate dredging of the channel at periodic intervals during a simulation.