Tillegra Dam Project,2011 Reservoir Design for Augmented Water Supply for Tea Gardens, 2040 Andrew Davis - z3253083 ShazaRifi - z3290972 AanchalChaturvedi - z3306945 Darren Penh - z3289870 Group 24
Scope of the Project • The township of Tea Gardens is situated on the northern foreshore of Port Stephens, NSW and was recorded to have a population of 2500 people in 2004. • A rapid increase in residential growth is expected over the next 30 years with a population of 85000 in 2040 predicted. • A dam at the Tillegra site is proposed to secure Tea Gardens with water in 2040.
Overview of the presentation • Estimation of water demand for Tea Gardens in 2040 • AWBM evaluation. Is it an appropriate model for use in Tea Gardens? • Dam height/Surface Area/Volume Relationships • Storage behaviour and proposed wall height under stationarity and climate change • Pipe Design and Routing
Assumptions on population Rapid increase in population to 85000. How did it get this big? • A mine has been established employing 2000 employees, bring people and families to Tea Gardens • Other residents drawn for ‘sea-change’. However with limited space in Tea Gardens, assumed 50% of residents will live in apartments • Both these assumptions will have a major influence on water demand in 2040
Water Demand Factors considered which influence water demand include; Population Type of Household Water Rates Industry Agriculture Tourism Seasonal and Diurnal Fluctuations
Population • Initial approximation of 7.135GL per year • Approximately 230L/per person/day
Household type • Assumed 50% of the population live in apartments • water usage in an apartment is 100L less per day than a house • These values determine a daily use of approximately 130L /person/apartment and 240 L/person/house. • New estimate of demand is 6.75 GL per year
Mining • Mine assumed to employ 2000 employees living in Tea Gardens. • An estimate of 4.33GL per year of water is required for production of coal. • Increased demand estimate from 6.75GL to 11.08GL per year
Seasonal Fluctuations • greatest weekly water consumption occurs in the summer months and with the least in the Autumn and Winter months of the year. • Peak monthly consumption of 633ML occurring in January
Diurnal Fluctuations • 210L/per person/day calculated earlier • 6 peak hours (6:00 - 9:00am and 6:00 - 9:00pm), • Using a 60:40 ratio and a conservative assumption that all water is consumed in this 6 hours only. This results in 126L of water per person (between 6:00 - 9:00am) and 84L of water per person between (6:00 - 9:00pm) • Maximum flow in pipes are 42L/per person/hour or 3.57ML/hour
Water Rates and attitude • As water rates increase, in the short term, a decrease in water use, per person, can be expected. • In the long term, a decrease in water consumption person can also be expected with the introduction of new water saving technologies and water saving campaigns. However, • A conservative assumption concluded that increasing water prices and improved attitude WILL NOT be a significant factor in determining the water demand required for Tea Gardens.
Industry, Tourism and Agriculture • Initial estimates from regional centres (e.g Coffs Harbour) included water use from industry, tourism and agriculture. • Excluding the coal mine, Tea Gardens was found to have no major Industry and agriculture which would cause demand to deviate from approximated value using regional centre total water consumption values. • Tourism similar to Coffs Harbour or Port Macquarie and influence on demand included in initial approximation also. Seasonal fluctuations due to tourism has been already accounted for.
Demand Conclusion • Demand for Tea Gardens township is 6.75GL per year based on assumptions made. This demand fluctuates due seasonal and diurnal influences. Seasonal peak of 633ML/month in January. Peak diurnal demand between 6:00 - 9:00am and 6:00 - 9:00pm • Demand for the coal mine 4.33GL per year, assumed constant throughout the year. • Total demand is 11.08GL per year
Model Evaluation AWBM model used to estimate runoff. However, is it a good representation of real runoff values? Evaluation process 2.5 years of rainfall and evaporation data run through MATLAB using AWBM. Comparison between real runoff data and model runoff then made.
Model Evaluation The AWBM plot is more linear in nature than the real data and acts similar to a ‘line of best fit’ for the real runoff values. Between approximately days 150-400 and 850-1096, the AWBM models the runoff very well and from this graph appears to be an appropriate method of modelling.
Model Evaluation • A boxplot of the data was also constructed to provide graphical comparison. Similarities between shape of the data can be seen however the AWBM model appears to ‘dampen’ the large runoff events. • This dampening effect will induce under-estimation errors in reservoir inflow calculations
Statistical Evaluation • Statistical analysis conclusively proves that the AWBM is an appropriate representation of the real runoff for Tillegra. Using a hypothesis test with a null hypothesis, Ho: mean model=mean real, and a level of significance (α) of 0.01, a P-value of 0.9677 results. • This gives us significant evidence to accept the null hypothesis that both the means are equal and verify the AWBM as an appropriate model for Tillegra.
Model Evaluation Conclusion All rainfall-runoff models have some related errors and the AWBM is no exception to this rule. However, It can be concluded from these different methods of analysis, the AWBM is an appropriate model for Tillegra runoff and is appropriate for use in storage calculations.
Approximating Surface Area • Tillegra Dam at AHD of 87m. • Surface area at AHD 90m, 100m, 110m, 120m, 130m and 140m approximated using scale map and transparent grid paper. • This gave a relationship between surface area and dam height, given by; SA (m2) = 4E-08h4 + 3E-05h3 + 0.0026h2 + 0.0076h + 0.0012, R² = 0.9999 • This equation allows the surface area to be approximated at any dam height (h)
Approximating Volume • Dead storage was set at 63708 m3 at 3m AHD • The trapezoidal rule was used utilising the surface areas calculated previously. • This yielded the following equation for Volume at height (h) • Volume (m3) = 6E-06h^4 + 0.0009h^3 + 0.0021h^2 + 0.0658h - 0.067, R² = 1
Storage Design Storage behaviour of the Tillegra dam was evaluated using the mass balance equation; St+1 = St + Qt – Dt – ΔEt –Lt; where St+1 is the storage at time t+1, St is the storage at time t, Q is inflow, D is demand, E is evaporation losses and L is other losses (e.g. environmental flows).
Inflow (Q) • Using Matlab and the AWBM, daily evaporation and rainfall data from November 1969 to November 2002 was analysed to give daily runoff values. These runoff values were then multiplied by the area of the catchment (205km2) to give a daily runoff in cubic metres. • The daily inflow data was then summed for each month to give total inflow (m3) for each month.
Demand (D) • Demand for Tea Gardens in 2040 was estimated at 11.08GL/year. • This was split into 6.75GL/year for the township, while 4.33GL/year was estimated for the mine that has been assumed to exist in Tea Gardens in 2040.
Evaporation (ΔEt) • Daily evaporation data (mm) was summed to give monthly totals. This total was then multiplied by the surface area of the reservoir, calculated from the height (h) of the dam wall.
Other Losses (L) • These include losses to aquifer, seepage under the dam and environmental flow. • Losses to the aquifer were neglected as the Williams River is a gaining stream, thus neglecting gives a conservative estimate • Seepage was assumed to be orders of magnitude lower than demand and was neglected.
Environmental Flow • Low flow for William’s River is 24ML/day • Moderate Flow for William’s River is 24-100ML/day • For Tillegra Dam, the Environmental flow was taken as 50ML/day • To fulfill the RFO’s, seasonal fluctuations based on average monthly inflow data was used, as can be seen below. • The 50ML/day was distributed with the seasonal fluctuations to account for natural variations. This will also account for low flow periods during drier months. • Also any overflow from the dam structure will account for required ‘flushes’. This environmental flow regime fulfills the RFO’s.
Other Model Factors • Other factors include; starting dam water level height, Robustness and Level of serviceability • A Level of serviceability of 100% was assumed • 50% of the capacity was decided as the starting dam water level height to be conservative • The Hunter water scheme for robustness (severity and frequency of water restrictions over a given time period) was accepted and can be seen in the figure and will be analysed for acceptability
Storage Behaviour Under Stationarity Conclusion • the dam wall be constructed to a height of 31m. • This gives a maximum capacity of 36.34GL (including dead storage), and a surface area of 3666071m2. • The critical period from the analysis is approximately 17 months. • level 4 water restrictions are only reached once for a length of 6 months over the 33 year period of analysis (1.5% of time period). It was concluded that the robustness of the proposed Tillegra Dam is acceptable.
Storage Behaviour Due to Climate Change • To estimate the impact of climate change on the storage calculations for Tillegra, the General Circulation Models (GCMs) were used, and more specifically the A2 envelope.
Storage Behaviour Due to Climate Change • To predict the variation in storage behaviour due to climate change at Tillegra in 2040, the GCMA2 simulation needs to be correlated with the local historical data at reservoir site. To do this the Constant Scaling Method was used. • Seasonal Averages for both precipitation and evaporation were calculated for the current climate (1960-1990) and the future environment (2030-2049). These then resulted in the ‘scaling factors’
Storage Behaviour Due to Climate Change Conclusion • the dam wall be constructed to a height of 33m. • This gives a maximum capacity of 43.85GL (including dead storage), and a surface area of 4208946m2. • The critical period from the analysis is approximately 17 months. • level 4 water restrictions are only reached once for a length of 6 months over the 33 year period of analysis (1.5% of time period). It was concluded that the robustness of the proposed Tillegra Dam is acceptable.
Pipe Routing • The general guidelines for pipeline routing are as follows, • Minimise overall pipe length • Parallel existing utility corridors (Highway, High tension Electric transmission line). • Avoid areas of high population density. • Minimise highways, railways, river, khals, canals, ponds, hills & mountains crossing to reduce the project cost. • Cross highways, railways, river, khals, canals at or close to 90 deg. angle. • Minimise crossover of existing facilities. • Provide adequate construction area.
Pipe Routing Also we need to avoid; • Swamps and Wetlands • Rocky areas • Unstable soil • Populated areas • Historical areas • Environmentally sensitive areas (Forest, Tea garden, Rubber garden etc.) • Religious sensitive areas (Mosque, Graveyard, temple etc.)
Pipe Routing • Based on these quantitative results, the Brown route is the most suitable • It is the shortest route (86.6 km), minimizing overall pipe length and overall construction cost. • It crosses a relatively little amount of waterways. This minimises environmental disturbance to the many rivers and creeks in the area during the construction phase. • It crosses a relatively little amount of forests and reserves. This minimises the environmental impact and reduces construction costs as there is minimal need for land acquisition.
Pipe Design • The maximum flow for January is 633 ML/month = 20.8 ML/day • Flow due to the mine, 4.33 GL/year = 11.87 ML/day • Max flow = (20.8 + 11.87) ML/day = 32.67 ML/day • This implies that the final maximum flow is 378 L/s. • We can calculate the hydraulic gradient by dividing the height of the reservoir by the pipe length.Our hydraulic gradient is 0.000436 m.
According to the table below, our pipe diameter is 0.8 m but for safety purposes we can assume it to be modified to 0.85 m.
Pipe Material Selection • PVC pipes can crack under freezing conditions and can become extremely brittle under prolonged exposure to UV. • To overcome these issues, High Density Polyethylene (HDPE) can be used. • HDPE is resistant to UV light. It is also reliable over a very wide range of temperatures and is also much more resistant to degradation and corrosion than most other plastic. • It is also safer to carry potable water.
Pipe Material Selection • PVC or HDPE pipelines offer considerable reduction in cost compared to concrete or steel pipes. • HDPE pipes offer considerable improvements in UV, degradation and temperature resistance over PVC. • HDPE has been selected as the pipe material
Pumping Stations • 5 pumps with locations; • Pump 1 (Dam Wall) • Pump 2 (5.8km) • Pump 3 (19.5km) • Pump 4 (34km) • Pump 5 (52.5km)
Environmental Concerns and Risks Social impacts; • Prior to constructing the dam, not only does land need to be cleared, but people also need to clear. Involuntary displacement of people is often the main social impact of such projects. • This will have little effect on Tea Gardens, however as the Dam is constructed outside the township. • Reservoirs have the potential to create an environment which is complimentary to the transmission of water related diseases. Proper treatment and management is required to ensure minimal impact on the community.
Environmental Concerns and Risks Environmental Impacts • forestry and vegetation needs to be cleared in the area to be flooded and monitoring the migration of fish and other aquatic organisms need to be considered • The loss of forests and agricultural land will also lead to erosion of the reservoir and the build up of sediment at the base of the river. • Sediments blocked behind the dam means that these nutrients may not reach farmland downstream of the dam and could reduce the fertility of the land. • The dam will also affect the temperature of the water and may result in the reduction of breeding of fauna.
Environmental Concerns and Risks Dam Failure • Dam failure has the potential to cause more death and destruction than any other structure! • following risks have a minimal possibility of occurring, however must still be considered during the dam design: • ‣ Overtopping of embankment : if the spillway is too small, and flood water rise too high, the dam will fail. • ‣ Faults in construction: use of the wrong construction materials may lead to internal erosion and pipe failures • ‣ Inadequate dam foundation • ‣ Landslides: Soil failure can be induced by large bodies of water, which may then send a wave of water over the top of the dam, causing it to fail. • ‣ Earthquakes: Dams can catastrophically fail due to an earthquake, however this occurrence is quite rare, and highly unlikely in the case of the proposed Tillegra Dam.