LOSA DEL OBISPO

etc.

Considering the above problems faced at the commissioning stage, it was decided to carry out a post evaluation of the system. In 2011 September, i.e, 20 months after commissioning a post evaluation was carried out in the distribution system. Three distribution subzones out of the 15 sub-zones of Meewatura system was selected for the post evaluation. The three zones were selected giving due consideration to pipe length, proportion of existing and new pipes, number of consumers, and location of the distribution sub-zone. It was decided to evaluate following parameters in the study;

1. Number of consumers 2. Water consumption

3. Water consumption pattern 4. Water losses

5. Nodal Pressure

The methodology of the study is depicted below.

At first a site reconnaissance had been carried out to verify that the pipe network operating at site is as same as the designed pipe network. Number of control points was identified by a careful study of the distribution map to cover new consumers areas, existing consumer areas, different elevations, system mid points and extreme ends. The pipe flows and nodal pressures were measured on site using the control points.

To establish water consumption and consumption pattern, monthly records of the bulk meter at reservoir outlet and hourly readings of the bulk meter for a period of 24 hours had been recorded.

The consumers in the three sub-zones were coordinated using GPS. The GPS readings were taken by the study team together with the meter readers covering the monthly meter reading cycles of the zones. By this method, it was ensured that all the consumers who are in the commercial data base of the NWSDB were mapped to the GIS. The water consumption was planned to be obtained from the commercial database, established by onsite monthly consumer consumption readings recorded by meter readers.

Table 6 gives the details of the selected three sub-zones and the control points.

Table 6 - Details of the Selected Sub-Zones Description Panabo ka Maligat ena Angun awala Design Water demand m3 ₍₂₀₂₅₎ 1200 3118 6564 Reservoir cap. m3 536 916 1750

Location Rural Semi

Urban Urban Elevation m MSL 655.4 594.8 588 Existing pipes m 310 5830 37,236 New pipes m 14,762 48,970 35,196 % existing pipes 2 10.6 51.4 No. Of control points 10 10 10

9. Results of the Field Study

At the site reconnaissance survey, few discrepancies were found between the actual site situation and the sub-zone pipe network model. The computer model is updated to depict the exact site situation.

Figure 10 - Theoretical & Actual Demand Patterns at 3 Reservoirs

Figure 10 shows the average water demand pattern of the three reservoirs.

The layout maps of the three sub-zones including the consumers are shown in Figures 11, 12 and 13.

In all 3 sub-zones, it has been found that the commercial database does not match with the actual site situation. Some consumers who are actually being served by other sub-zones are entered incorrectly to the study zones and some

7 Reservoir Predicted domestic water demand 2011 Calculat ed 2011 (Avg) Measured consumpt ion (Avg) Panabokka 547 290.6 128.1 Maligatenna 1881 1731.7 943.6 Angunawala 3678.4 4396.3 2939.9 consumers relevant to study zones are found to

be recorded in other areas.

The water consumption of the sub-zones was re-evaluated with the consumers assigned to their correct sub-zones. Table 7 gives the outcome of the consumer mapping.

Figure 11 - Layout Map of Panabokka

The predicted water demand, water demand calculated with actual average number of consumers using the same design criteria used for predictions with an NRW of 15% and the average consumption calculated using four months actual water meter readings are tabulated in Table 8.

Table 9 gives the calculated water loss of each sub-zone during three months study period considering different sets of data.

Table 10 gives the nodal pressures at the control points. The installation of bulk meters to measure the flow could not be carried out as planned.

Table 7 - Number of families/ consumers

Reservoir As per pop. survey As per commercial DB (Aug) After GIS (Aug) Panabokka _{817 461 408} Maligatenna _{2473 2088 2146} Angunawala _{4673 5885 5817}

Figure 13 - Layout Map of Angunawala Table 8 - Water Demand Predicted and Actual (m3_/d)

10.

Analysis of Results

Figure 12 - Layout Map of Maligatenna

The expected number of consumers as per the design has not been achieved in the rural areas. This may be due to cost constrains. In semi urban areas number of consumer connections has reached about 87% of the expected value and in urban areas consumer number has exceeded the predictions.

The water demand of the zone varies in correlation with the number of consumers. The demand calculated using the number of consumers is from 53%-92% of predicted. The measured water demand is 23%-80% of the predicted. This necessitates further studies to

8

NRW% Angunawala Maligatenna Panabokka

Sep Oct Nov Sep Oct Nov July Aug Sept

Calculated with onsite bulk meter measurement 44.2 48.07 39.61 41.3 54.5 37.2 26.7 52.3 30 Calculated with onsite minimum night flow 39.2 42.05 NA 59.8 46.6 25.6 6.9 13.2 27.6

verify the assumption of per capita demand and percentage NRW assumed in the system. The possibility of having pipes related to adjacent sub-zones being connected with the incorrect sub-zone shall also be checked. The minimum average monthly consumption per connection varies from 0.25-0.46 m3_{/d (10.4-19.2 l/h).} Assumed peak factor 2, has been justified for the system. A slight variation in the assumed demand pattern is seen with respect to each reservoir and the relevant consumer base. This could be due to varying consumer behaviour in the sub-zones.

Table 9 - Calculated Water Losses

Table 10 - Pressure at Control Points

Figure 14 - Flow Error Curve of Water Meter

Control

point Angunawala Maligatenna

Panabokka 15.08. 2011, 12.30-15.30

Design Onsite Design Onsite Design Onsite

1 20.3 36 26.14 22 23.4-28.3 28.0 2 34.1 28 34.75 32 33.7-36.5 40.0 3 45.4 40 48.35 50 25.2-42.2 48.0 4 50.5 58 62.66 60 47.0-47.5 45.0 5 55.5 52 70.06 62 42.2- 48.9 54.0 6 69.4 42 80.46 50 49.9-50.8 46.0 7 76.4 66 83.96 62 72.0-73.6 74.0 8 86.3 78 79.49 78 74.0-86.8 90.0 9 90.2 80 93.39 60 88.9-90.7 85.0 10 91.5 48 64.75 58 74.0-88.3 92.0

The NRW is varying from 26.7% - 54.5% in the three subzones. The minimum night flow has been varying from 6.9%-59.8%. Upon checking the water leak records of the sub-zones it is noted that most of the leaks are occurring in the service connections.

High NRW recorded in the system could be due to several reasons;

1. The commercial database does not match with the real number of consumers relevant to the respective sub-zone.

2. The billing cycle could be varying. 3. Percentage of existing pipes in the

system is high.

4. Delay in reporting and attending the water leaks creating high water losses 5. Water meter errors.

6. Low leakage rate and long duration of leaks in service connections.

The water meters used in the system are rotary piston type water meters. As per the manufacturers catalogue the main technical data (Table 11) and the flow error curve (Figure 14) [7], when the consumption per connection is less than the recommended minimum flow of the water meter, errors could occur in the meter readings. Old water meters in the system will give erroneous meter readings.

Presenting water losses as a percentage of production fails to take into account the main

9