Storage and pumping capacity analysis using hydraulic modeling

Transcription

1 Storage and pumping capacity analysis using hydraulic modeling G. MacPherson City of Chilliwack, B.C., Canada W. de Schaetzen & S. Cripps GeoAdvice Inc., Vancouver, B.C., Canada ABSTRACT: This paper summarizes the hydraulic network modeling study to assess the existing and future storage and pumping capabilities of the Chilliwack Mountain area (Chilliwack, BC, Canada). Development in the Chilliwack Mountain area will be significant in the next 15 years. This study determined that the current storage and pumping capacities of Chilliwack Mountain will not be able to support these new developments. Infrastructure upgrade strategies are developed and modeled to determine the most cost-effective way to eliminate the deficiencies in the Chilliwack Mountain water system over the next 15 years. Improvement projects including storage tank, pump, valve and pipe upgrades are recommended. This study demonstrates that a complex hydraulic network model can be used as a practical tool for the optimal planning of network upgrades to meet fire flow requirements. Enhancement of water distribution infrastructure planning, operation, and management are principal benefits to the city of this study. 1 INRODUCTION Water distribution networks, pump stations, and storage tanks are usually designed to accommodate projected population growth. As the population continues to grow, however, periodic reassessment and planning is required to assure that the system can accommodate the continued growth. When poor performance and low reservoir levels are observed, then the system will require assessment to determine the best course of action to take to restore system performance and also to enhance the system to accommodate future population growth predictions. Timing of system upgrades is also an issue as the construction must be completed under budget and before operational performance drops below acceptable levels. A properly calibrated hydraulic network model of the water distribution system as well as future population predictions are required for accurate assessment of the required future storage and pumping capabilities. 2 DATA COLLECTION AND REVIEW Table 1 List of data provided by the City of Chilliwack Item Name/Description Format WaterCAD model CD Lickman Rd. booster station Paper test results Pump station SCADA Paper screenshots population projections spreadsheet Subdivision and land pdf development bylaws Map of development area Paper 2005 water quality annual report Paper Zone 2 pump station daily Paper volume Feb 06 Oct Design criteria review The design criteria presented in the City of Chilliwack Subdivision and Land Development Bylaws were reviewed to ensure appropriate water system upgrades. The criteria included, but were not limited to, water demand unit rates, minimum pressure criteria, storage and pump capacity criteria, and fire flow requirements. Table 1 below lists key data that were provided by the City.

2 Figure 1. Trend line used to extrapolate Chilliwack Mountain population. 3 POPULATION PROJECTION EXTRAPOLATION AND DEMAND SCENARIO CREATION Population was estimated using population projections from the City of Chilliwack from 2006 to 2015 and a linear extrapolation method. The choice of extrapolation method is due to the limited land area available for feasible development on Chilliwack Mountain. In fact, large areas of the mountain are too steep for future development, limiting the population growth. The population in 2020 was deemed to be 3,000 using the linear extrapolation method as shown in Figure 1. Using the per capita daily demand criteria (taken from Chilliwack Subdivision and Land Development Bylaw 2004, No ), the projected total demand for Chilliwack Mountain in 2020 was calculated for three cases: Average Day, Maximum Day, and Peak Hour. The total demands for the 2006 population as well as the 2010 population were also calculated. Using these calculated demands, the global demand multipliers associated with each future scenario were then calculated using the 2003 demands as a base (WaterCAD base modeling scenario was 2003 ADD). The results are shown in Table 2 below using the peaking factors shown in Table 3. Note that the demands do not include fire flow requirements, which, at 150 L/s, is almost 3 times the 2020 maximum day demand. 2. Total demand for 2006, 2010 and 2020 scenarios Year Scenario Total demand L/s 2006 Average day demand 6.22 Maximum day demand Peak hour demand Average day demand 8.09 Maximum day demand Peak hour demand Average day demand Maximum day demand Peak hour demand Table 3. Demand peaking factors Demand scenario Peaking factor MDD/ADD 3.02 PHD/ADD 5.04 PHD/MDD 1.67 Using information provided by the City Staff about future development, the extra demand was allocated accordingly. Most of the development is expected to take place in Chilliwack Mountain Zone 2. Furthermore, it was expected that a total of 300 single family residential and townhouse units would be built on the south side of Zone 2 and 360 units would be built on the north side by By using the population values given for 2006, 2010 and the extrapolated 2020 population, the amount of additional demand from each side of Zone 2 was determined. Table 4 lists the total calculated demand for Zone 2. Table 5 lists the future demand calculated for each year and the junction to which the demand was allocated to.

3 Table 4. Total demand for 2006, 2010 and 2020 scenarios Year Scenario Total Demand L/s 2006 Average day demand 4.30 Maximum day demand Peak hour demand Average day demand 6.17 Maximum day demand Peak hour demand Average day demand Maximum day demand Peak hour demand Table 5. Future demand and allocation Year Additional North side South side Population demand* demand** L/s L/s , * Junction J-1109 ** Junction J Fire flow criteria assessment Required fire flow demands were determined for each node based on the city s proposed land use in each zone. These fire flow demands were then allocated to each node in the model. The design fire flow criteria were obtained from the Chilliwack Subdivision and Land Development Bylaw 2004, No The fire flow allocations for the Chilliwack Mountain zones are shown in Table 6. Table 6. Fire flow requirements by zone Zone Fire flow requirement L/s 2 60 & 150* * for land use type R-4 (multi-family) 4 SYSTEM ASSESSMENT To assess the system and determine possible upgrades, simulations were run using the current model. These simulations include steady-state, fire flow and EPS. This section details the results of these simulations. Table 7. Hydraulic modeling results (no improvements) Scenario Average Nodes with Nodes* with pressure pressure < 44psi pressure < 44 psi psi # % 2006 PHD PHD PHD *Total number of demand nodes is Fire flow modeling results (no improvements) Fire flow demands were also assigned to all nodes in the model based on land use data provided by the City Staff and Chilliwack design requirements. The simulations predicted some fire flow deficiencies in the existing system under maximum day demand conditions. As shown in Table 8, the deficiencies are already present in the current network under present day demands, and by 2020, 11 of the 40 fire flow nodes in the Chilliwack Mountain area will experience residual pressure less than 22 psi. Table 8. Fire flow modeling results (no improvements) Scenario Average available Deficient fire Deficient fire MDD+FF fire flow flow nodes flow nodes* L/s # % *Total number of fire flow nodes is 40 It is evident that the existing pipes sized 150 mm are too small to accommodate the required fire flow demands of 150 L/s as well as the velocity limit of 6 m/s. Using the maximum velocity criteria of 6 m/s, the flow rates as shown on Table 9 are obtained. Table 9. Pipe sizes and flow rates* Diameter Maximum flow mm L/s *maximum velocity is 6 m/s 4.1 Hydraulic modeling results The initial hydraulic modeling results indicated a number of deficiencies present in the system. From Table 7, it is evident that a number of nodes experience residual pressure below 44 psi, which is the City of Chilliwack minimum requirement.

4 d = 150 mm d > 150 mm Fire Flow = 150 L/s To be upgraded Figure 2. Existing 150mm pipes connected to fire flow nodes requiring 150 L/s Figure 2 shows the existing 150 mm pipes connected to fire nodes requiring 150 L/s. Those pipes must be upgraded or duplicated in order to satisfy the maximum velocity constraint. PRV stations were also reviewed in terms of peak velocity under Maximum Day + Fire Flow condition. To limit the amount of wear and tear, the recommended peak velocity through a PRV should be less than or equal to 6 m/s. 4.3 EPS modeling results (no improvements) Besides the steady-state analyses, an extended period simulation was also set up and run. Running an EPS is required for evaluating the water system over time as opposed to the instantaneous results obtained from a steady-state analysis. Issues related to reservoir and storage tank water levels can only be analyzed through EPS modeling. As the Chilliwack Mountain model contained no diurnal pattern for EPS modeling, a pattern was developed for use in the EPS simulation which was approved by the City. This pattern is shown numerically in Table 10 below. This pattern was used for all EPS simulation runs for the study. Since the land use of interest is residential only, a non-residential diurnal pattern was not built. The PHD / MDD peaking factor for resi- dential land use is 1.67 which is consistent with Table Diurnal pattern values Start time Value Start time Value Start time Value 0: : : : : : : : : : : : : : : : : : : : : : : : The following were completed for the EPS modeling: 1 Define EPS parameters such as duration, and hydraulic time-step; 2 Assign diurnal pattern to all demand nodes in Zones 2, 3 and 4; and 3 Run a 24-hour EPS to analyze storage adequacy of tanks in 2006, 2010, 2020.

5 Figure 3. Tank level variation 24-hour EPS simulation no improvements (2020 MDD scenario) Simulations did not run for a full 24-hour EPS for the 2010 and 2020 scenarios due to the Zone 2 tanks becoming empty during the EPS. Figure 3 shows the tank level variations for the Zone 2 tanks under the EPS conditions. It is apparent that from this figure that the tanks do not refill when the system is subject to the 2020 maximum day demand conditions using the existing infrastructure. 4.4 Pumping capacity analysis Table 11 shows the pumping requirements for 2006, 2010 and 2020 as they compare to the pumping capacities of the Chilliwack Mountain Zone 2 Pump Station. This station is responsible for pumping all water to feed Chilliwack Mountain Zones 2, 3 and 4. The existing pumping capacity corresponds to manufacture pump curve while the actual pumping capacity is based on the 2006 field measurements. 11. Required and existing pump capacities Year Required pump Existing pump Actual pump capacity * capacity ** capacity*** L/s L/s L/s *Corresponds to MDD zones 2, 3, & 4 **Manufacturer s pump curve ***2006 field measurements It is evident from Table 11 that the existing Zone 2 Pump Station does not provide adequate pumping capacity in From Table 11, it is clear that the pump station that feeds Zones 2, 3 and 4 will have to be upgraded as soon as possible. 4.5 Tank storage analysis Storage requirement is a key design criterion for distribution systems. There are three types of storage volume which need to be considered in the water system: 1 Fire storage (A) This is the amount of water required to extinguish fires within the service area of a tank or booster station. This storage is typically based on the worst case land use scenario. 2 Equalization storage (B) This is the amount of storage required for normal water consumption. The City of Chilliwack bylaws state that this should be 25% of maximum day demands. 3 Emergency storage (C) The emergency storage requirement in the City of Chilliwack is 25% of equalization and fire storage combined. Any deficiencies in these storage requirements can be supplemented through pumping and augmentation of water supply and transmission capacity. Using the future population data, as well as the tank capacities derived from data in the WaterCAD model, the required storage capacities for the 2006, 2010 and 2020 populations were estimated. Tank volumes were determined by taking the maximum water level of the tank and multiplying it with the area of its cylindrical base. Table 12 below shows the calculated volumes and capacities and a calculated total storage of 1.52 ML. 12. Calculated tank volumes and storage capacities Reservoir Maximum level Diameter Volume Capacity m m m 3 ML Zone 2A Zone 2B Zone Zone

6 The above calculated capacity values were then compared to the projected capacity requirements for Chilliwack Mountain. These capacity requirements were calculated using the future population projections, the daily per capita demand flow values and the tank storage requirements bylaw. The comparisons are displayed below in Table 13. As can be seen from Table 13, there is currently not enough storage to meet even today s storage requirements. Most of the required capacity comes from the large fire flow storage requirement. With the 150 L/s fire flow requirement, the storage deficiency will be 1.11 ML by Immediate upgrading of the current storage tanks is recommended. Since most of the development will occur in Zone 2, a zone analysis of the storage capacity of Zone 2 was conducted. Results are shown in Table 13. There is currently a large deficiency in storage capacity in Zone 2. This is, again, due to the high fire flow requirements for the area. Immediate upgrade of the storage capacity is required. 4.6 Proposed improvements Water system improvement projects have been developed and are recommended based on the assessment of the water system under future growth conditions. These projects were developed to satisfy the long-term requirements of the Chilliwack Mountain area. These suggestions include storage tank, pump, valve and pipe upgrades. To assist the City in budgeting, the various project recommendations were consolidated into work projects. Table 14 summarizes the recommendations. A total of 6 upgrade projects are recommended with a total estimated cost of $3,400,000 (2006 CAD$). The most immediate concern is the upgrading of storage capacity in Zone 2, as the existing capacity is already inadequate for current requirements. Pump capacity upgrading must also take place now, as the existing pump station is not able to provide adequate pumping. Another urgent concern is the duplication of pipes required to satisfy the velocity constraint of 6 m/s (Project ID: 1). Table 15 lists three operational changes. Table 14. Summary of proposed infrastructure upgrades Project Year to Project Description Estimated type implement ID cost CAD$2006 Pipe 2006/10 1 to km of pipe 1,750,000 duplication (200 mm) Valve new PRV (200 mm) 100,000 Pump new PS (2 x 80 HP) 750,000 Tank Additional storage in 800,000 zone 2 (1.4 ML) 15. Proposed PRV operational changes PRV ID Current Proposed Year to setting setting implement psi psi Grandview Drive PRV Shrewsbury Lower PRV Shrewsbury Upper PRV The above upgrades (infrastructure and operational changes) provide a water main network that meets the City of Chilliwack design criteria. The hydraulic model with the proposed improvements was run for a 10-day extended period simulation (EPS). The pump controls of the proposed pumps were also adjusted for the future EPS runs to ensure that the storage tanks properly refilled. Figure 4 shows the tank level variations under the EPS conditions. It is apparent that the tanks refill when the system is subject to maximum day demand conditions when all the improvements are constructed. Figure 5 shows the upgrades and their locations. 13. Comparison of current storage capacity and requirement Year Zone Population Fire flow Equalization Emergency Required Existing tank Excess / deficient storage A * storage B storage C A + B + C storage storage ML ML ML ML ML ML ,3,4 1, ,3,4 1, ,3,4 3, *150 L/s fire flow for 2 hours

7 Figure 4. Tank level variation 10-day EPS simulation with improvements (2020 MDD Scenario) Future Pipes Existing Pipes Project 1 200mm Pipe in // Cost: $158k 1 3 Project 3 200mm Pipe&Valve in // Cost: $548k Project 2 200mm Pipe in // Cost: $734k Figure 5. Locations of proposed upgrade projects Project 4 200mm Pipe in // Cost: $393k 4 5 Project ML new storage Cost: $808k Project 5 2 x 80 HP new PS Cost: $750k

8 5 CONCLUSIONS AND RECOMMENDATIONS The City of Chilliwack required a water assessment of the Chilliwack Mountain water distribution system. 5.1 Conclusions The following is a list of key conclusions drawn while performing the storage and pumping capacity study: 1 The City of Chilliwack design criteria used for the study were compiled using the 2004 Subdivision and Land Development Bylaws as well as information provided by the City Staff. The critical design criteria selected for use in the study included: per capita demand requirements; minimum fire flows; minimum and maximum static pressure; and existing and projected population data. 2 Water demands were estimated for 2006, 2010 and 2020 scenarios. The current peak hour day demand is 31 L/s which is expected to increase to 78 L/s by Hydraulic modeling results (no improvements) indicate that 18% of the nodes experiences residual pressure less than 44 psi in Fire flow modeling results (no improvements) indicate that approximately 22% of the nodes cannot provide the required fire flows with 22 psi residual pressure in Tank storage analysis indicates that the current storage capacity in Zone 2 does not meet present day requirements. The most immediate concern is the upgrading of storage capacity in Zone 2, as the existing capacity is already inadequate for current requirements. 6 Pumping capacity analysis indicates that the pumping station in Zone 2 does not meet present day requirements. Pump capacity upgrading must take place now, as the existing pump station is not able to provide adequate pumping. 7 In total, 6 improvement projects are recommended with a total estimated cost of $3,400,000 (CAD 2006). 8 Incorporating the upgrades into the model provides a network that meets the City of Chilliwack design criteria. 2 Consideration of water quality within the distribution system and storage tanks should be incorporated into the modeling and analyzed. 3 The City should review their rate structure and Development Cost Charges (DCC) in the light of the high cost of recommended upgrades. 4 Consider re-running the analyses using revised criteria to complete a sensitivity analysis and reevaluation of recommended upgrades. 5 Before the City commits to moving forward with the recommended improvement plans, the City should consider re-calibrating the hydraulic model to reflect physical changes that have taken place in the network since it was last calibrated. 6 REFERENCES Chilliwack Subdivision and Land Development Bylaw 2004, No Recommendations Based upon the findings from our analysis, the following is a list of recommendations: 1 Integrate Chilliwack Mountain sub-model with the entire Chilliwack model and confirm boundary conditions, supply HGLs, for validating the proposed improvement projects.