Robust algorithm for head-dependent analysis of water distribution systems

In a water distribution system (WDS), low pressure situations can arise for a variety of reasons. For example, over time, the demands may exceed the capacity of the WDS or some major components e.g. pumps and trunk mains may not be operational while repairs are carried out. The extent to which demands are satisfied in a WDS is governed by the actual amount of pressure in the system and pressure-deficient operating conditions are not uncommon. Despite this, the conventional modelling approach works well only under fully satisfactory pressure regimes, with results for subnormal pressure conditions often being inaccurate, misleading and even unreasonable. Sample results for a prototype FORTRAN computer program which can perform head-driven analysis using a globally convergent Newton-Raphson scheme are presented. Extensive testing has shown that the program is efficient and robust. It is demonstrated here that head-driven analysis is not computationally more time consuming than demand-driven analysis and that different functions for head-dependent nodal outflows can produce significantly different results.