Estimation of Reservoir Storage Capacity and Maximum Potential Head for Hydro-Power Generation of Propose Gizab Reservoir, Afghanistan, Using Mass Curve Method

The present study objective is to estimate reservoir storage capacity and maximum potential head for hydro-power generation of the proposed Gizab multipurpose dam site in the Upper-Helmand river basin, Afghanistan. The mass curve is used to estimate the reservoir capacity and maximum potential head for power generation with the utilization of various years mean monthly flow data of the Upper-Helmand River Basin at the proposed Gizab dam site.The reservoir volume is 4709.12 Mm3at 1435m elevation form mean sea level with reservoir capacity of 1114.3 Mm3 with annual average inflow of 100.9m3/s and annual demand of 100m3/s. The net potential head of the proposed Gizab site is 117m with power generation of 91.822 MW with using of Francis turbine efficiency of 80%.


INTRODUCTION
In order to professionally operate reservoirs for hydropower generation, irrigation, and flood control, the management of water quantity within the reservoir is required (Salami et al., 2012). Beside volume of water in the reservoir the water surface elevation within the reservoir can be an indication of available storage. These relationships between elevation and storage volume, similar to area-volume and elevationarea relationships makes it possible that engineers can find fairly accurate value of one parameter from the other (Magome et al.,2003). From surface water resources the adequacy and reliability of the water supplies for deferent propose are dependent upon the ability of reservoirs to make available sufficient water storage during the critical dry periods (Bharali, 2015). But these surface storage reservoirs also face many problems for their decrease of safe yields such as increases in water demand due to increases in population and gradual loss of reservoir capacity yield because of sedimentation in the reservoirs. For water resources management the remote sensing and GIS is a supplementary solution, therefore, this techniques provide cost and time-effective estimation of storage capacity, require little human supervision, free of secretarial barriers or political interference, and must be demonstrably reliable over long periods and in all kinds of weather (Salami et al., 2012). Remote sensing data is used to provide elevation contours and water spread area of each contour and volume of reservoir at different water levels of a reservoir.

II.
STUDY AREA The proposed Gizab reservoir (Fig. 1) is a multi-propose project across the Helmnad river basin, Afghanistan. The proposed reservoir is located between 33° 22' 10"N and 33° 33' 25" N and 66° 10' 00" E and 66° 27' 40" E. The length of the reservoir is measure about 43 km in length and 15.10 km in width at its longest and widest point of reservoir. The reservoir surface area is 74.82 km 2 in 1435m elevation from mean sea level with volume of 4709.12 Mm 3 . Hight of the proposed Gizab reservoir catchment area is varying from 1299m to 5036m w.r.t mean sea level ( Fig. 2) with area of 22070 sq km. The catchment area is embodied by large hills, buried pediments, vallies and alluvial plains. The soil textures are silty clay, sandy, loamy and alluvium. The upper-Helmand river basin originated in a westerly extension of the Hindu Kush mountain range near Paghman about 40 kilometers west of Kabul and runs southwesterly to the proposed Gizab reservoir. The river water runoff comes mostly from rainfall at the average elevations of the

Mass Curve
A cumulative plotting of net reservoir inflow versus time duration is a mass curve (or Ripple diagram, 1882) and is expressed as: (1) Where V (t) = Volume of runoff and Q (t) = Reservoir inflow, both as function of time. At any point on the mass curve the slope of the tangent of that point shows the rate of flow at that point on the mass curve and expressed as Q (t) = dV (t)/ dt (2) In the design of a reservoir storage capacity, operations procedure and flood routing the mass curve hasvaluable applications. Mass curve preparation procedure is given below: Plot mass inflow curve from the flow hydrography of the site for a number of consecutive years Plot the mass demand curve corresponding to the given rate of demand. Draw the tangential line parallel to the mass demand curve at peak point of mass inflow curve Determine the vertical intercepts between the tangential lines and the mass inflow curve. Determine the largest of the vertical intercept determined in step (4). The largest vertical intercept represents the storage capacity required.  Fig.4. Power generation is always depending on two important parameters discharge and head of water from upstream to downstream. Penstock is conveying water from storage reservoir to powerhouse with turbines. The power potential of flowing water is function of discharge, specific weight of water and head between turbine and reservoir active storage capacity level. Hydro-Power potential of water is express mathematically as below: P = ƞ γ Q H(3) Where P = Power (W) γ = ρ g = Specific weight of water (N/m3) ρ = Mass density (kg/m3) = 1000 kg/m3 for water g = Acceleration due to gravity (m/s2) Q = Discharge (m3/s) H = Head (m) Ƞ = hydraulic turbine efficiency and its typically value is taken from  Fig. 3 the turbine was selected for the propose Gizab reservoir  Vol-4, Issue-11, Nov-2017]  https://dx.doi.org/10.22161/ijaers.4.11.15  ISSN: 2349-6495(P) | 2456-1908(O) www.ijaers.com

Hydro-Power Potential Head
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IV. RESULTS AND DISCUSSION
The relief of the proposed Gizab reservoir catchment area is 3737m. The contours elevation of the proposed reservoirin proposed site is started from 1310m to 1530mfrom mean sea level and carried out by Global Mapper 18. Therefore, reservoir area and volume of each contour is carried out form ASTER DEM using Global Mapper 18and Arc-GIS 10.3 which is given in Table 2.The relationship between elevation -volume and relationship between elevation-area is shown in Fig. 5. Finally the gross potential head of the reservoir full supply level to powerhouse is 130m and the net potential head is 117m with 10% head loss in the conveying. Ten percent of total reservoir storage capacity is used for dead storage capacity of sediment trapping for the design period. The volume of dead storage capacity is 470.912 Mm 3 which is coming under the contour of 1349m height from mean sea level.

International Journal of Advanced Engineering Research and Science (IJAERS)
[ The mean monthly discharges are given in Table.3 the maximum discharge is 310.347 m 3 /s in the month of June and the minimum discharge is 30.119 m 3 /s in the month of December. The average discharge of 12 month is 100.899 m 3 /s. The reservoir storage capacity form the mean monthly inflow is driven from mass curve is 1114.356 Mm3 Fig.6. Also the reservoir storage capacity is driven analytically from monthly mean inflow Table.3. V. CONCLUSION  The reservoir capacity is the most important aspect for hydrologic design.  The reservoir capacity is design for mean monthly inflow data of several years using Mass Curve method and the storage capacity is 1114.3 Mm 3 .  The gross storage volume of the proposed Gizab reservoir is 4709.118 Mm 3 and carried out from ASTER DEM using Global Mapper 18 and Arc-GIS 10.3.  The gross potential head of the reservoir full supply level to powerhouse is 130m and the net head for the generation power is 117m with 10% head loss of gross potential head at system operation.  The Francis turbine with 80% efficiency has used for the study.  At available head with use of Francis turbine and its efficiency of 80%, the hydropower potential is 91.822 MW.