RATING OF TUNGABHADRA LEFT BANK CANAL TUNGABHADRA DAM, KARNATAKA

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1 RATING OF TUNGABHADRA LEFT BANK CANAL TUNGABHADRA DAM, KARNATAKA Dr S Sampath 1, N.P. Khaparde 2, B. Suresh Kumar 3 1, 2, 3 (Central Water and Power Research Station, Pune, Maharashtra, India, sreekanth.sampath@gmail.com) Abstract The management of water resources depends, to a considerable degree, on the availability of hydrological and hydraulic data. The operation and maintenance of irrigation systems requires collecting regular data on water levels and discharges. The calibration of canal sections or structures provides information on canal discharges and hence supports the efficient day-to-day water management and regulation of irrigation systems. The Tungabhadra Dam is constructed across the Tungabhadra River, a tributary of the Krishna River. The dam is near the town of Hospet in Karnataka. It is a multipurpose dam serving irrigation, electricity generation, flood control, etc. This is a joint project of Karnataka, Andhra Pradesh and Telangana after its completion in The water level profiling was done by CWPRS at the CH 28 in mile 1 during August 2014, March 2015 and August 2015 using Acoustic Doppler Current Profiler (ADCP)[8] and Current Meter[1].The measurements were performed simultaneously with the two methods to present a comparison of discharge measurement made by current meter[14] which is the conventional method[2][3] and latest developed technique, ADCP[13]. Results show that the relative error is very small with the ADCP over the conventional method. Besides the total value of discharge, the ADCP method also offers detailed information about velocity distribution over the cross section. 1. INTRODUCTION Tungabhadra dam Project (Figure 1) is an interstate, Multipurpose Project between the two states viz. Karnataka and Andhra Pradesh. The Project consists of a High level masonry dam constructed across Tungabhadra River near Munirabad town in Koppal Districts of Karnataka State. The reservoir upstream of Tungabhadra dam has a storage capacity of about 120 TMC. The water from this reservoir is used for generating 126 MW of electricity and irrigating 3, 62,800 Ha of agricultural lands in Karnataka and Andhra Pradesh. Water from the dam is released in to the Left Bank Canal (LBC) and is utilized for power generation and irrigation in the Karnataka state. Three power houses are constructed on the LBC, one at the foot hill of the dam, and other two are at Shivapur and Sanapur. Tail water from the dam power house is carried to Shivapur and Sanapur reservoir through LBC. Tail water of Shivapur power house is released in to LBC. The length of LBC is about 225 km in Karnataka, Operation and maintenance of this canal is under control of Irrigation Department, Government of Karnataka. Estimation of canal discharge at the head at CH 28 in Mile 1, is therefore very significant. Fig 1: Tungabhadra Project 2. TUNGABHADRA LEFT BANK CANAL Tail water of dam power house and irrigation sluices release flow into Tungabhadra left bank canal. The canal is lined and is designed to project carry discharge of 116 m3/s (4100 ft3/s) at head. It has an irrigation potential of 2,43,900 hectares in Karnataka. The left bank canal traverses for a length of 225 km in Karnataka. Fig 2: Location map of Tungabhadra Dam Left bank canal Volume: 04 Issue:

2 A. Gauging site at ch. 28 in mile 1. The canal in this section is lined and is designed for 116 m3/s (4100 cusec) at the head. A cross regulator is situated on ch.28 in mile 1 which regulate the flow in the Tungabhadra left bank canal. Fig 2 show the location of map of Tungabhadra left bank canal. A permanent gauging site on the canal is located at ch.28 in mile 1. A cross section of the canal at the above site is given in Figure 3. A permanent foot bridge is constructed at one km downstream of the site at ch. 28, which facilitates depth and velocity measurements across the width of the canal. A gauge well is constructed on the right bank of the canal at the site. The view of the foot bridge of the canal is shown in Figure 4. A. Objective Studies were conducted in Tungabhadra Left Bank Canal at ch.28 in mile 1, for different gauge levels to find out corresponding discharges and establish gauge discharge correlation for the above gauging site [15]. B. Methodology The discharge in the canal was measured by Area-Velocity method as prescribed in BIS 1192: 1981 and ISO 748: 1997 using Current Meter & Echo Sounder [1]. The discharges in the canal were also measured and confirmed by Acoustic Doppler Current Profile (ADCP) using River Surveyor instrument for better accuracy [13]. Fig 3: Cross section of canal at ch. 28 in mile 1 4. DISCHARGE MEASUREMENT USING AREA VELOCITY METHOD A. Gauge Observations For confirmation of stable flow condition at the gauging site, gauge observations were made at a regular interval from two to three hours prior to commencement of discharge measurements and also during the period of discharge measurements. It was observed that zero at the average bed level of the canal i.e. depth measurements and gauge readings were same. A gauge plate graduated in feet was mounted on the inside wall of the gauge well. Figure 5 depicts the view of the gauge well at site. The gauge data, as observed during these studies, is given in Table-1. B. Depth measurements using Echo Sounder The canal section of base width m (83.53 ft) at ch. 28, was divided into 7 equal segments to cover the flow having uniform depth. Two segments were marked on either sides for lower water level and four segments were marked for higher water level to cover the flow in the sloping bank canal portion. Depths were measured at the center of each of the vertical using Echo sounder, where sufficient depth was available. Sounding rod was used to measure the small depths in the end segments. Details of verticals are shown in Figure 6. Depths were measured at the start and end of the measurements and average value was taken as the depth for computation of area of the segment. Figure 4: Gauging site at km FIELD MEASUREMENTS The field studies were carried out at the canal site for gauge and corresponding discharge at the gauging site. The observations were confined to the discharge range as indicated below. Discharges from m3/s (2564 ft3/s) to m3/sec. (4392 ft3/s). During the field measurements, the discharge in the canal was gradually increased from lower to higher water depths. Different sets of observations were carried out for different water levels in the canal [14]. C. Velocity measurements using Current Meter Velocity measurements were subsequently taken at the verticals located at the center of each of segment. Velocities were measured at 0.2, 0.6 and 0.8 depth from the surface. Velocity measurements were carried out using self-recording propeller type current meter average velocity on each vertical of a segment was worked out as: Discharges were computed using values of areas of the segments and average velocity of the segment as per the midsection method given in IS 1192:1981 Volume: 04 Issue:

3 Figure 5: Gauge well on LBC at ch. 28 in mile 1 Various observations were carried out for different gauge levels in canal ranging from 10.1 ft to 12.5 ft at the above site in August 2014, March 2015 and August Details of these observations are given in Table 1. Fig 6: Depth / Velocity verticals across LBC at ch. 28 in mile 1 D. Computation of Discharge using Current Meter and Echo Sounder The average of the three velocities observed on a vertical was taken as the mean velocity of flow through the segment. By knowing the width, depth and mean velocity of the flow, the discharge passing through each segment was worked out using mid section method as explained in BIS 1192: 1981 and ISO 748: Total discharge in the canal was then obtained by adding all the segment discharges. The discharge data, as observed on different days, is given in Table - 1. E. ACOUSTIC DOPPLER CURRENT PROFILER The main external components of an ADCP are a transducer assembly and a pressure case. The transducer assembly consists of nine transducers that operate at a fixed, ultrasonic frequency, typically Dual 4-beam 3.0 MHz/1.0 MHz, Janus 25 Slant Angle, 0.5 MHz Vertical Beam Echo sounder. The pressure case is attached to the transducer assembly and contains most of the instrument electronics. When an ADCP is deployed from a moving boat, it is connected by Bluetooth to a portable laptop. The computer is used to program the instrument, monitor its operation, and collect and store the data. Fig 7: Discharge measurements using ADCP at ch 28 in mile 1 5. OPERATIONAL PRINCIPLES: The ADCP measures velocity magnitude and direction using the Doppler shift of acoustic energy reflected by material suspended in the water column. The ADCP transmits pairs of short acoustic pulses along a narrow beam from each of the four transducers. As the pulses travel through the water column, they strike suspended sediment and organic particles (referred to as scatterers ) that reflect some of the acoustic energy back to the ADCP. The ADCP receives and records the reflected pulses. The reflected pulses are separated by time differences into successive, uniformly spaced volumes called depth cells. The frequency shift (known as the Doppler effect ) and the time-lag change between successive reflected pulses are proportional to the velocity of the scatterers relative to the ADCP. The ADCP computes a velocity component along each beam; because the beams are positioned orthogonally to one another and at a known angle from the vertical (usually 20 or 30 degrees), trigonometric relations are used to compute three-dimensional watervelocity vectors for each depth cell. Thus, the ADCP produces vertical velocity profiles composed of water speeds and directions at regularly spaced intervals. ADCP discharge measurements are made from moving boats; therefore, the boat velocities must be subtracted from the ADCP measured water velocities. ADCP s can compute the boat speed and direction using bottom tracking (RD Instruments, 1989). The channel bottom is tracked by measuring the Doppler shift of acoustic pulses reflected from the bottom to measure boat speed; direction is determined with the ADCP on-board compass. If the channel bottom is stationary, this technique accurately measures the velocity and direction of the boat. The bottom-track echoes also are used to estimate the depth of the river (Oberg, 1994). ADCP discharge measurements are made by moving the ADCP across the channel while it collects vertical- velocity profile and channel-depth data. The ADCP transmits acoustic pulses into the water column. The groups of pulses include water-profiling pulses and bottom-tracking pulses. A group of pulses containing an operator- set number of waterprofiling pulses (or water pings) interspersed with an operator-set number of bottom- tracking pulses (or bottom pings) is an ensemble ; a single ensemble may be compared to a single vertical from a conventional discharge measurement (Oberg, 1994). A single crossing of the stream Volume: 04 Issue:

4 from one side to the other is referred to as a transect. Each transect normally contains many ensembles. When depth and water velocities are known for each ensemble, an ADCP can compute the discharge for each ensemble. The discharge from all transect ensembles are summed, yielding a computation of river discharge for the entire transect. ADCP operational parameters (such as depth-cell length, number of water and bottom pings per ensemble, and time between pings) are set by the instrument user. The settings for these parameters are governed by canal/river conditions (such as depth and water speed) and also by the frequency and physical configuration of the ADCP unit (RD Instruments, 1989). F. Measurement Procedure using ADCP The Hydro boat carrying the ADCP is traversed from one end to the other end of the canal across the section. The measurement of discharge using the river surveyor system comprises of three components viz., Start Edge, Transect and End Edge. ADCP calculates the total discharge by summing the Start Edge, Top Estimate, Measured Area, Bottom Estimate and End Edge. Only the Measured Area is calculated by ADCP and all other areas are calculated by a technique known as Velocity Profile Fig 8: Pixel data collection across the canal using ADCP Extrapolation using power law velocity profile, which is inbuilt in the software. At least four cycles of measurements are taken by ADCP for each gauge observation and the average of four measurements are computed during data processing. Likewise for different gauges the procedure is repeated and the observations are tabulated, the measurement observation using ADCP at the gauging site is shown in Figure 7. An insight of the pixel data across the canal is shown in Figure ANALYSIS OF FIELD DATA The technical features/specifications as described above clearly show that accuracy of ADCP is higher than the current meter used for measurements in the canal. Hence, data collected by the ADCP and Current Meter is compared and better results are incorporated in Table 1. The gauge and discharge data as observed on Tungabhadra Left Bank Canal at ch 28 in mile 1 is given in Table 1 and the same is plotted in Figure 9. This plot indicates that relationship between gauge and data is non-linear. A statistical analysis of this data using method of least square, revealed following relationship between depth of flow and discharge. Q=7.483 G2.524 Where Q = Discharge in ft3/sec and G=Gauge / Flow depth in feet. The above relationship has a correlation coefficient (R2) = It would be seen that the correlation coefficient is very high and the standard error (0.0031) is well within the reasonable limit i.e., 5%. The results of the statistical analysis thus indicate that the quality of field data is very accurate and the error in estimation of discharge will, therefore, be very small. A rating curve and a chart, prepared on the basis of above relationship, are given in Figure 9 and Table 2 respectively. It may, however, be mentioned that the above rating curve and chart should be used within the observed range of data. Any extrapolation of the rating curve / chart may likely to cause additional error. It is also mentioned that the rating curve / chart is valid as long as the site conditions under which the field measurements were carried out are not changed i.e., no silting or no scouring of canal bed canal lining not disturbed or removed no weed growth in the canal, the downstream cross regulator gates kept fully opened and location of gauge well and zero of the gauge not changed. TABLE 1: GAUGE DISCHARGE DATA OF TUNGABHADRA LEFT BANK CANAL AT CH 28 IN MILE 1 S. N o Date Discharge Time of Gauge measured by Gauging in Hrs. reading ADCP in Feet From To ft 3 /s m 3 /s Fig 9: Gauge-discharge curve of Tungabhadra LBC at ch. 28 in mile 1 Volume: 04 Issue:

5 TABLE 2: RATING CHART OF TUNGABHADRA LEFT BANK CANAL AT CH 28 IN MILE 1 Gauge(G) in ft Discharge(Q) in ft 3 /s Discharge (Q) in m 3 /s ii)rating curve and rating chart based on above statistical relationship are given in Figure 9 and Table 2 respectively. REFERENCES [1] BIS 1192: 1981, Velocity area methods for measurement of flow in open channels. [2] Herschy RW (1985), Stream flow measurement, Elsevier Applied Science Publishers [3] ISO 748: 1997, Measurement of liquid flow in open channels Velocity are methods [4] Chen YC, Chiu CL (2002) An efficient method of discharge measurement in tidal streams. J Hydrol 265(1 4): [5] Chiu CL, Chen YC (2003) An efficient method of discharge estimation based on probability concept. J Hydraul Res 41(6): [6] Lemon, D. D., D. Billenness and J. Lampa, Recent advances in estimating uncertainties in discharge measurements with the ASFM. Proc. Hydro 2002, Kiris, Turkey. [7] Maidment, D.R., Handbook of Hydrology, McGraw-Hill, New York. [8] Nihei, Y., Irokawa, Y., Ide, K., and Takamura, T. (2008) Study on River-Discharge Measurements using Accoustic Doppler Current Profilers, Journal of Hydraulic, Coastal and Environmental Engineering, vol.64, No.2, pp [9] Oberg, K.A., and Schmidt, A.R., 1994, Measurements of leakage from Lake Michigan through three control structures near Chicago, Illinois, April October 1993: U.S. Geological Survey Water- Resources Investigations Report , 48 p. [10] Operational Hydrology Report No. 13; WMO - No. 519, World Meteorological rganization,geneva. [11] Rantz, S. E., Measurement and computation of streamflow, Volume 1, Measurement of stage and discharge, [12] Sauer, V. B. and R. W. Meyer, Determination of error individual discharge measurements, U.S. Geol. Survey. [13] Teledyne RD Instruments (2006) Acoustic Doppler Current Profiler Principles of Operation a Practical Primer. [14] WMO 1980 Manual on Stream Gauging. Vol I, Fieldwork. Vol II, Computation of Discharge. [15] Technical Report No 5348, January 2016, CWPRS, Pune RECOMMENDATIONS Based on the field studies for rating of Tungabhadra Left Bank canal at ch 28 in mile 1. carried out by CWPRS, Pune following recommendations are made: i) The gauge and discharge data is given in Table 2 and plot of gauge vs. discharge is given in Figure 9. A statistical analysis of the above field data revealed following relationship between gauge and discharge of the best fit curve. Q = G Where Q = Discharge in ft3/s and G = Gauge / depth in feet. Volume: 04 Issue: