Different ANN Models Selected on The Basis of Different Parameters
Chapter 7 Development of Reservoir Simulation Model
7.3 RESULTS AND DISCUSSION
7.3.1 Proposed Measures for Minimizing Diurnal Variation
Considering the constraints of practical feasibility and requirement of meeting power demand, the following approaches have been developed for minimizing diurnal variation of flow.
Structural measures: Regulating-pond at downstream Non-Structural measures: Regulated turbine operation a) Structural Measures: Regulating-Pond at Downstream
Several measures for minimizing variation of flow downstream of the dam have been thought about and simulation has been carried out to visualize the effect of such measures, Structural measure is one of the measures thought for the minimization of diurnal variations.
A new idea of introducing a small capacity pond downstream of the reservoir was investigated to explore possibility of minimizing diurnal variation and to analyze its performance and practical feasibility. In this approach, we propose construction of a regulating pond downstream of the turbine for regulating high discharge released from the turbine during operational hours. The size of this pond will depend on the installation capacity of the project and amount of regulation envisaged. Analysis of the terrain has also shown that it will be possible to create such storage just at downstream of the dam without raising the tail water level, i.e. without reducing the net head. Simulation study has shown that diurnal variation of flow could have been significantly minimized by creating a downstream storage of 36 Mm3. Fig 7.9 shows the curves showing the ranges within which
the downstream will vary if a 5m high barrier covering the entire width at 4Km downstream of the dam is placed.
Fig 7.9 Comparisons of inflow, downstream flow, operating hour and non-operating hour flow
Fig 7.10 presents the comparisons of non-operational hour flow i.e. the flow downstream when the turbine is not in operation with natural inflow. The plot also shows the duration of non-operational hour flow downstream. It depicts that non-operating hour flow is following the same patter as the natural inflow. From the Fig 7.10 it seems clear that the duration of operational hour flow in a day in lean season is high which means in a day flow downstream is quite similar to natural flow condition that in fact is good to sustain the environmental equilibrium. This condition is favorable for downstream river biota to adapt harmoniously with natural environment and to maintain the life cycle. Fig 7.11 is the plot of operating hour flow, natural inflow and the duration of flow. The operating hour is little high as compared to inflow but overall it follows the same trend. Hence implementation of the structural measure ensures the more or less similar flow both in operating hour and non- operating hours without compromise of the power production.
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Discharge (m3/s)
Period (10 days)
Inflow
Downstream Flow Operating Hr Flow Non-operating Hr Flow
Fig 7.10 Plot of inflow, non-operating hour flow and duration of flow.
Fig.7.11 Plot of inflow, operating hour flow and duration of flow.
Though the results were quite exciting, this option has been found practically difficult due to following facts:
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Non-operating Hr Flow (m3/s)
Period (10 days)
Inflow Non-operating Hr. Flow Duration of Flow
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Duration (Hr)
Operating Hr Flow (m3/s)
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Inflow Operating Hr Flow
Duration of Flow
i). Width of the stream is about 4Km at that section with wide flat valley, which will require marginal embankment up to the foothill portion. Marginal embankment will obstruct flow of three streams on left and one stream on right into the Subansiri River. Obstruction of stream may cause flooding upstream of these streams in the flood period.
ii). As the water level during flood time is high a huge staging of about 4Km length and of about 30 m height will be required for gate operation. Apart from the constraint of cost, possibility of damage to such structure during flood time cannot be ruled out.
iii). Reservoir will continue to release sediment through the orifice spillway of the dam.
Though initially the sediment load will be reduced, considering the sediment load of the stream, it is expected that the flow released through the spillway during flood period will still contain enough sediment, which will get deposited in this downstream storage space, as velocity of flow will drop significantly. This will reduce the capacity of such storage within a short period. As such in long run function of this small storage may not be effective.
b) Non-Structural Measures: Regulated Turbine Operation
However, though total flow volume in ten days remains more or less same before and after construction of dam, rate of flow in the downstream varies significantly.
Non-structural measures: the number of turbines to be operated in different time period is regulated as per the following two options.
i) Operating one turbine continuously at full capacity and operating rest of the turbines simultaneously for maximum possible duration, so that effort can be made to utilize the available water in the reservoir for meeting peak power demand. This approach is proposed basically to minimize duration of occurrence of high flow discharge at downstream and to create a near natural flow condition in the downstream for a longer duration.
ii) Operating one turbine continuously for 24 hours and increasing the number of turbines one by one, so that a turbine once put into operation can be run for maximum possible hours subject to water availability. By this approach high rate of flow at downstream due to simultaneous operation of all turbines as proposed in ‘option a’ can be minimized to a great extent, of course with the compromise of peaking power.
Overall performances of these options are analyzed through simulation study and presented below.
Non-structural measure-I: Operating One Turbine Continuously and Operating Rest of the Turbines Simultaneously : Option of providing minimum flow of around 300 m3/s in the lean period to produce 250MW power continuously by running one turbine for the entire day and to produce 1750MW with the remaining water for the possible period. This will ensure minimum flow of 300m3/s throughout the day in the lean period with maximum flow of around 2500m3/s for the peaking duration, which will not be less than 2 hours per day even in the lean period. Fig 7.12 shows the plot of maximum, minimum downstream flow and natural
Fig 7.12 Comparison of inflow, operating hour flow and non-operating hour flow
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Discharge (m3/s)
Period (10 days)
Inflow
Operationing Hr Flow Non-operating Hr Flow
inflow rate with one turbine running continuously. Fig 7.13 shows the plot of minimum downstream flow, its duration in a day and natural inflow rate with one turbine running continuously. Fig 7.14 shows the plot of Maximum downstream flow, its duration in a day and natural inflow rate with one turbine running continuously.
Fig 7.13 Plot of inflow, non-operating hour flow and duration of flow
Fig 7.14 Plot of inflow, operating hour flow and duration of flow
Non-structural measure-II: Operating One Turbine Continuously and Increasing the Number of Turbines One by One: Another option of utilizing the available water by running
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Duration of Flow Operaating Hr Flow
one turbine continuously and then increasing the number of turbine one by one for maximum possible hours of operation for each of the added turbine. This will restrict maximum rate of flow, off-course with a compromise with peaking power. Fig 7.15 shows the maximum and minimum rate of flow through turbines along with the plot of natural inflow.
Fig 7.15 Comparisons of inflow, operating hour flow and non-operating hour flow
Fig 7.16 Plot of inflow, non-operating hour flow and duration of inflow
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Discharge (m3/s)
Period (10 days)
Inflow
Operating Hr. Flow Non-operating Hr. Flow
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Duration (Hr)
Non-operating Hr.Flow (m3/s)
Period (10 days)
Inflow Non-operatign Hr Flow Duration of Flow
Fig 7.16 shows the inflow, non-operating hour flow and the duration of flow. Fig 7.17 shows the inflow, operating hour flow and the duration of flow.
Fig 7.17 Plot of inflow, operating hour flow and duration of flow