Introducing Velocity Index for Water Distribution Systems

Abstract

Planning and hydraulic modelling phase in Water Distribution Systems (WDS) are playing an enormous role for water authorities. Making wise decisions in planning phase will ease the future recurrent budget for Capital Expenditures (Capex) and Operating Expense (Opex) to guarantee achieving the acceptable quality of service in WDS encountering population growth and land developments. The conventional methodology for planning of WDS includes the population growth impact assessment on the system and then proposing new assets to comply with the local water distribution code. Potable water networks need asset planning, augmentation strategies and rehabilitation schemes in consistence with the new assigned loads to them. Planning strategies are usually based on sophisticated hydraulic models and a determined and pre-defined time intervals to maintain the level of service after occurrences of increase in design serviced population, asset ageing and/or serviced area. Systems rehabilitation studies require significant amount of budget which is the main constraint for the water authorities for the implementation of any augmentation plan. Two main factors are playing roles in WDS asset planning strategies. The first parameter is the acceptable Level of Service and the second factor is the “Associated Cost” of the asset planning. The main goal of a proper planning in a WDS is the prediction of a system’s behavior in future and suggestion of efficient set of solutions for the predicted demand. The most critical criteria to be addressed and augmented in a typical urban WDS are water pressures and water velocities. Water pressure is the first tangible measure that customers feel and the water velocity has impact on energy loss in the system which is an indicator of applied shear stress from water to inner side of the pipes. The water pressure and the water velocity are two main hydraulic factors which are affected by population growth and therefore capital expenditure needed to rectify them. Authors earlier introduced a Pressure Index (PI) for WDS and studied the relationship between PI improvements and augmentation costs per connection. Authors’ earlier publication considered the modification and improvement of pressures in the water systems. In the current paper, development and calibration of further hydraulic models (using Innovyze InfoWorks WS model) for water systems are presented. In addition to the introduced PI factors, in this paper a new index (Velocity Index, VI) is introduced for the assessment of WDS from the water velocity point of view. Relationships between improvements of Level of Service (considering VI) and “Associated Cost” in WDS are presented.