Articles & Case Studies

FloodFlow introduces graphical flood flow path modelling for WinDes®

Posted: Wednesday 10th October 2007

Sales of bookshelves to engineers have probably soared in the wake of the stream of regulatory publications emanating fromEurope, central government, the regional authorities, the Environment Agency and professional bodies. Aidan Millerick, managing director of Micro Drainage Ltd, discusses the central requirement of risk assessment, and describes a new analysis and modelling module that addresses the key challenges it presents to engineers.

Exceptional rainfall events such as Carlisle, Boscastle and York have made flooding a significant political issue. Indeed, emerging climate change patterns suggest that we may have to review our definition of “exceptional”.

As a result, the emphasis for approval and regulatory scrutiny is rapidly shifting towards risk assessment, rather than simply testing for failure. Moreover, flooding at nodes is no longer the primary concern - it is where the water goes that is determining the destiny of proposed developments.

Regulatory compliance

The most significant regulatory requirements for civil engineers and their clients all set out new criteria for planning approval, in which risk assessment and sustainability are central themes. They include:

The long-term performance of the system is a key consideration for the regulations covering the taking in charge process. These are covered by the Sewers For Adoption (SFA) standards in England, Wales and Scotland, and the Regional Drainage Policies in Ireland.

Protection of existing river catchments is covered by the guidance set out in the Interim Code of Practice for SUDS and CIRIA C697 and C698 - the SUDS manuals.

There are no shortcuts for engineers seeking to familiarise themselves with these regulations. Yet the pressure to maintain productivity, and deliver accurate results against increasingly tight deadlines, can make it difficult to introduce risk-based design and analysis to the acceptable standard. Automation is essential for engineers seeking to maintain and enhance productivity, while achieving compliance with the demanding new approval requirements.

WinDes already incorporates a wealth of functionality to assist with compliance in all these regulatory areas. The new FloodFlow module brings an enhanced capability to the suite that directly addresses the primary concern of approving authorities: the risk to property from flooding.

By enabling the development of dynamic models of flood flow paths, FloodFlow gives engineers the ability to test systems for regulatory compliance and present robust proof of the integrity of their analysis.

It is a quick and efficient way of organising the complex data required for risk assessment into manageable, easily understood reports, with clear 3D visual representations of the results.

Key functions

FloodFlow works in conjunction with the triangulated terrain maps available within the WinDes Advanced Productivity Tools (APT). It works by splitting the terrain into a uniform grid, the size of which is defined by the user. The program provides Explicit or Alternate Direction Implicit (ADI) calculation options, and there are four calculation modes.

Mode 1, the Geometric Mode, allows the triangulated surface terrain to be analysed without flow. The lines of steepest gradient are displayed on each triangle, and flat areas are identified. Ridge lines and sink points are also shown, allowing the optimum gulley positions to be located.

In Mode 2, the Fixed Depth mode, a fixed depth of rainfall may be applied to the entire terrain and allowed to flow for a short time. Maximum depths and velocities are shown. Fixed Depth mode provides validation of the findings of the analysis in the Geometric Mode.

Mode 3, the Static mode, is used to identify flood flow paths after modelling events in the WinDes Simulation module. Flood volume leaving a manhole is routed across the terrain and overland flow paths are identified.

The analysis is volume aware; the water fills surface depressions before flowing on. Note that no provision is made for water re-entering the drainage network when analysing flow in Static mode.

In Mode 4, the Dynamic mode, Simulation and FloodFlow analysis are completed in a single pass. Water can leave the system at manholes or across the sides of an open channel, and flow back into the system at open sections or non-surcharged manholes further down the overland flow path. Volume is maintained throughout the calculations, to give a dynamic simulation of real flows.

In Dynamic mode, water moving in the 2D terrain model is removed from the 1D system model, and then returned to it if the terrain model shows water flowing back into the system. Using the Simulation module within APT, worst-case depths and velocities are presented initially, with actual depths and velocities shown during animation of the event.

Multiple analysis timesteps and surface types can all be specified by the user, and results can be presented in the WinDes Plan or 3D WorldView.

The 3D visual capabilities of WinDes allow the creation of detailed representations of the site, complete with buildings and other landscape features. If the system fails, the affected properties can be identified virtually door by door.

FloodFlow enables engineers to model events in fine detail, demonstrating the critical storms and, crucially, the capacity of their designs to accommodate them, leaving vulnerable properties unharmed.

With FloodFlow, the surface terrain can now be fully introduced into the design of the system as a whole, and, where acceptable flow paths are shown, can actually become an active contributor to the mitigation of flooding. With sustainability commanding equal attention from approving authorities, this capability introduces a valuable new asset for integration with SUDS systems and conventional controls: the land itself.

Visit www.microdrainage.co.uk for more information or telephone Micro Drainage on +44 (0) 1635 582555




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