Water Supply Configuration and Water Losses - Nikšić Waterworks Case Study - page 01

The Nikšić Water Supply System - Present Condition

Water supply for the City of Nikšić is secured from two water sources:

  • Vidrovan – capped springs, located 15 km north of the City, with a capacity from 250 to 450 l/s;
  • Poklonci – groundwater abstraction from wells, located 5 km east of the City, with a capacity of 200 l/s.

The Vidrovan source, located at an elevation 664 masl, is a primary water source and it operates continuously. Spring water is capped and is transported by gravity into the system. There is no additional retention volume or water tank at the Vidrovan source. Water quality meets water quality standards and only disinfection (chlorination) is applied. Most of the time (usually 9 - 10 months a year), this source has sufficient capacity for covering the water demands of the Nikšić system.

The Poklonci well source, located on the shore of Lake Krupac, comprises a total of 5 wells, with a capacity of approximately 40 l/s each. This source provides additional water quantities to the system only during the summer, when the Vidrovan spring flow drops to 250 - 300 l/s. Similar to Vidrovan, water is only chlorinated and there is no water tank constructed at the source. Water is pumped directly form the wells into the distribution system.

The Nikšić distribution network covers the City and several adjacent settlements, with a total of about 65,000 inhabitants. The lower pressure zone, located between 600-and 650 masl covers the majority of the area. The water demand of this zone accounts for 95% of the total demand of the system. The higher pressure zones exist in only a few isolated areas, located at elevations above 650 masl. Water for supplying consumers at higher elevations is pumped from the lower pressure zone, and at present there is a total of seven pumping stations. Three of them have been installed, not due to high altitudes, but due to insufficient discharge capacity in some parts of the lower zone, which leads to low pressures during peak consumption.

The "Duklo" booster pump station (hereinafter - Duklo BPS) is the vital structure in the system, as it is this facility through which nearly the entire water demand is being distributed into the system. Duklo BPS is located on the northwest border of a densely populated urban area and has the following characteristics:

Duklo BPS: Q = (1 + 1) x 400 l/s, H = 55 m

Water from the Vidrovan source is being transported gravitationally to the Duklo BPS, through a 15 km long ɸ 1000 pipeline. Simultaneously, during the summer period, water from the Poklonci wells is being directed to the upstream point of the Duklo BPS, through a 5 km long ɸ 500 pressure pipeline. The fact that ɸ 1,000 inlet pipes (from the Vidrovan source) and ɸ 500 (from the Poklonci wells) are directly connected, immediately upstream of the Duklo BPS, is of great relevance for the system operation. Downstream from this point of connection, water from both sources is being transported to the Duklo BPS, (through a 200 m long ɸ 1,000 pipeline) and from there these quantities are being pumped to the distribution network.

Downstream from the Duklo BPS water is transported through main distribution lines ɸ 700, ɸ 400 and ɸ 300 placed along major urban roads.

The main water tank in the system is reservoir Trebjesa, built on a hill in the southeastern part of the city. It is located on the opposite side of the distribution network from the water sources, and has the following characteristics:

Reservoir "Trebjesa" (R Trebjesa):
BA/OA = 691/697 masl, V = 7.500 m3

This water tank was initially designed to balance water flows that come from the water sources and the water demand. It was designed to be filling with water during low water demand (usually during the night) and to release water into the system during high water demand (during the day), effectively acting during peak demand as an additional water supply source for the distribution system. The main pipeline that connects Duklo BPS and the R Trebjesa was designed and optimized for this kind of operation. However, the elevation of the R Trebjesa is too high, which leads to unnecessarily high pressures in the distribution network: the majority of consumers are located at levels between 600 and 630 masl, while the working level in the tank is 695 masl. Therefore R Trebjesa was removed from the system operation, and all water demand, including peak demand, are being supplied only via the Duklo BPS. This distribution network has not been reconstructed to allow for this new way of operation, which leads to increased flow velocities in pipes, high hydraulic losses and increased pressure variations within the distribution network. It is a known fact that significant pressure variations are one of the main causes for pipe material fatigue which leads to frequent pipe bursts and increased water losses, which in turn increase water demand and further decrease pressures in the system, resulting in water shortages. This is true of the Nikšić water supply system, where low pressures and water shortages have been evident during peak demand in peripheral parts of the water supply network, especially in its southern parts which also leads to increased electricity consumption of the Duklo BPS.

Estimated values of the average annual water demand, billed water consumption (without losses) and water losses, as per data from the PUC Waterworks for the past several years, are given below:

Average water demand (yearly average)
Q av yearly (system) = 400 l/s

Billed consumption (yearly average)
Q av yearly (system) = 125 l/s

Water losses ≅ 70 %

The above defined water losses include both real and apparent losses, but additional investigations are needed to quantify these components.

Such a high quantity of water losses also lead to low seasonal water demand variations:

Monthly demand variation:
Q max monthly = 440 l/s; K max monthly = 1,10

Daily demand variation:
Q max daily = 480 l/s; K max daily = 1,20

where:

  • Q max monthly (system) – the maximum monthly water demand ;
  • K max monthly – ratio between maximum and average monthly demand;
  • Q max daily – the maximum daily water demand;
  • K max daily – ratio between maximum and average daily demand;

Billed water consumption (yearly average), is divided into the next three categories:

  • Households (population): 100 l/s (80 % of the total billed consumption)
  • Industry: 20 l/s (16 %)
  • Other small commercial customers: 5 l/s (4 %).

Since the total population number connected to the Nikšić water supply system is 65000, the demand and consumption per capita values are as follows:

 

Tab01

 

It should be noted that the "households" category includes both consumers in houses and in flats in buildings, which usually have different consumption per capita and consumption patterns. As per the limited available data, it can be concluded that water consumption per capita is higher in individual houses than in flats. Also, the category "Industry", in addition to industrial consumers, includes consumption of institutions (schools, hospitals, barracks, administration, etc.). The "Industry" category used to be the dominant water consumption category in the past, but economic collapse of the majority of industries in the City, the introduction of newer technologies in the remaining operational industrial facilities, as well as a shift of industries towards exploitation of private water resources instead of using water from the public waterworks, led to a multi-fold reduction in overall industrial water consumption in the past two decades.