Water Supply Configuration and Water Losses - Nikšić Waterworks Case Study - page 06

The proposed solution, which is essential to accomplishing the above objectives, dramatically change the system work concept and achieve the objectives, listed above, is contained in the implementation of the following measures:

  • Construction of the Vidrovan tank (R Vidrovan, min/max water levels = 659/664 masl, volume V = 1.800 m3), at the water source location – aimed at eliminating flow in partially full pipe in the outgoing pipeline DN 1000 mm, under all operational conditions. Additionally, this tank volume will provided the much needed volume for equalization of inequality of input flow and consumption of households connected to pipeline between the Vidrovan source and the Duklo BPS. At present, the total net average annual consumption in the area of future influence of the R Vidrovan, amounts to 15 l/s, while the estimated present consumption and demand in area covered by R Vidrovan, are:

net Q av yearly = 15 l/s
gross Q av yearly = 50 l/s (P leakage = 70 %)
gross Q max daily = 80 l/s (K max day (system)) = 1,2
Comparing the new R Vidrovan volume of 1,800 m3,

with an estimated maximum daily water demand in the area of future influence of the R Vidrovan, it can be concluded that the tank volume is about 35% of max daily demand.

  • Construction of the Uzdomir tank (R Uzdomir, min/max water levels = 650/654 masl, volume V = 5,500 m3), on the slopes of Uzdomir hill in the northwestern part of the City's suburban area. This structure should be located near the downstream section of the supplying pipelines (diameter 1000 mm and 500 mm, from two water sources), with connecting pipelines to enable a total water quantity input from Vidrovan and Poklonci into R Uzdomir, without any damping of flows. R Uzdomir will be located at an elevation that is appropriate for the supplying part of the lower supply zone located below 630 masl. The purpose of this facility is to provide volume for regular supply of central City area, which covers almost half of the current consumption in the system, and to provide in the central City area stable pressure at reduced level (2-4 bars), compared to the present condition;
  • Separation of lower subzone from the rest of the network, by closing off certain pipes or using "on/off" valves in the existing system. The objective is to properly delineate the zone that is supplied from R Uzdomir, which cover area between altitudes 600 – 630 masl. The estimated present consumption and demand in area covered by R Uzdomir, are:

net Q av yearly = 45 l/s
gross Q av yearly = 150 l/s (P leakage = 70 %)
gross Q max daily = 180 l/s (K max day (system)) = 1,2
R Uzdomir volume is about 35% of max daily demand

  • Construction of booster station BS Center in the downstream border of the lower supply zone, below Trebjesa Hill. The function of this booster station is to enable proper filling of R Trebjesa. In the reconstructed system, R Uzdomir will be supplied with 480 – 80 = 400 l/s - which reporesents the entire water production minus the water demands of consumers connected to the main pipeline from R Vidrovan. Water from the R Uzdomir will be transported by gravity into the above described subzone, in an amount which comprises of both the local water demand (180 l/s max daily demand) and the transfer flow for the rest of the network (220 l/s max daily demand). BS Center will pump water from the subzone into R Trebjesa. In this manner, R Trebjesa, which has been out of operation for several years will be re-introduced into the system, but in a different role. The pressurized discharge pipeline from the Center BPS and R Trebjesa is only 400 m long without any consumer connections, and the operation of the booster pumping station should be optimized taking into account the water level in R Trebjesa, current demand, energy consumption and other factors. It is foreseen that Center BPS should contain a total of three operational and one standby pump, each with a 80 l/s flow and a 65 m head;
  • Installation of a pressure reducing valve at the entrance to each of the peripheral zones of consumption - according to the proposed concept, R Trebjesa will operate as a distribution tank for the peripheral part of the system, which will be separated from the remaining network (area supplied from R Uzdomir). The area that will be supplied from R Trebjesa will cover a much larger area compared to that of the central subzone, but will have a similar water demand (220 l/s comparing to 180 l/s). R Trebjesa will supply the area which has already been divided into DMAs for purposes of leak detection. Each DMA has a single entry - supply pipe. Installation of pressure reducing valves at the entrance to each DMA has been proposed in order to reduce pressures due to too the high elevation of R Trebjesa. It is important to note that implementation of pressure reducing valves for pressure reduction in the central supply subzone DMAs (the central city area) will not be possible because of the presence of a multi-ring network and difficulties in establishing appropriate and manageable DMAs (unless a large-scale reconstruction/rebuild of the distribution network is done, which is deemed unfeasible).
  • Exclusion of the Duklo BPS from regular system operation – realization of the previously described measures will eliminate the need for regular operation of the Duklo BPS, which represents one of the basic ideas of the proposed concept. However, it is foreseen that this facility will be needed in the system only under extreme conditions (extreme consumption, the need for excessive flows for firefighting etc.). Therefore, this facility will become standby booster station.

 

Fig07
Figure 7: General system longitudinal profile after realization of concept alteration.

 

It is estimated that the realization of the described measures will achieve multiple positive effects:

  • Achieving a higher level of service throughout the distribution network;
  • Gravitation, as a dominant mode of flow in the distribution system will be established, which will result in more stable pressures;
  • Significant pressure reduction in the network (lower pressures, due to the presence of R Uzdomir in the central subzone; reduction of pressure - produced by the inlet from R Trebjesa, at the entrance to the each of peripheral zones);
  • Appropriate water tank volume will be provided;
  • Electricity consumption will be significantly reduced, due to reduced power of operational pumping stations and decreased volumes of pumped water;
  • Available source capacity can be used to its full extent, and according to the actual needs of the system;
  • The existence of excessively high and variable pressures in the distribution network will be practically eliminated, which will lead to a significant reduction in frequency of occurrence of pipe bursts and leakage.

In addition, it is emphasized that the solution with the closed valves, located at the boundary between the lower altitude zone (area of R Trebjesa influence) and the subzone (R Uzdomir), although not frequently used in standard engineering practice, seems to be very flexible. In accordance with the expected increase of consumption per capita, in addition to a reduction in losses due to implementation of the proposed rehabilitation measures, water demand will be changing in time, which will produce changes in division of total consumption between these two areas of the future system network. But, in accordance with the actual situation in the system, the separation between the two sub-zones will be easy to relocate by simple manipulation of existing valves in the network.

Preliminary analyses show that savings due to lower operational costs (electricity consumption, consumption of disinfectant agents, etc.) and higher water bill collection will offset and surpass the estimated costs of implementation of the described measures, including the measures for comprehensive modification of the system concept, described above.

 

Acknowledgement

This paper is an outcome of the International project: Networking for Drinking Water Supply in Adriatic Region, with acronym "DRINKADRIA", funded by the EU through IPA Adriatic.