Presentation on theme: "1 The Proposed Polavaram Project- Analysis of Water Availability vs. Water Use Luna Bharati, B.K. Anand and Vladimir Smakhtin Hyderabad, August, 2007."— Presentation transcript:
1 The Proposed Polavaram Project- Analysis of Water Availability vs. Water Use Luna Bharati, B.K. Anand and Vladimir Smakhtin Hyderabad, August, 2007
2 The Proposed Polavaram Project- Analysis of Water Availability vs. Water Use Outline Study Objectives WEAP-Model Setup –Defining spatial area –Scenario development –Defining water supply and demands Results from Scenario Analysis Conclusions
3 The Proposed Polavaram Project- Analysis of Water Availability vs. Water Use Objectives Quantify water availability/ water supply vs. water use/ water demand for: –Water use in the sub-watersheds (Mandals) falling under the Polavaram link command area. –Areas outside of the command area that will be affected by the Polavaram project i.e. Author Cotton Barrage area, Left bank and the Prakasham Barrage area The water supply and water demand was assessed for: 1) The current situation 2) After the Polavaram reservoir and link canal
4 WEAP - “ Water Evaluation And Planning” system Stockholm Environment Institute U.S. Center Highlights Integrated water resources planning system that runs on a monthly time step Built-in models for: Rainfall runoff and infiltration, evapotranspiration, crop requirements and yields, surface water/groundwater interaction, and instream water quality A database maintains water demand and supply information to drive mass balance model on a link-node architecture Embedded linear program solves allocation equations Minimal requirements: runs under Windows 98/2000/NT/XP on a Pentium computer with 256 MB RAM
5 Drainage map extracted from SRTM. http://srtm.csi.cgiar.org /SELECTION/inputCo ord.asp http://srtm.csi.cgiar.org /SELECTION/inputCo ord.asp Sub-catchments delineated from 5th order stream outlets. Link command area was divided into 7 sub-catchments 1. Model Setup-Determining Spatial Extent
6 The command area mandals were grouped into sub-catchments
8 2. Scenario Formulation Scenario 1: Reference Scenario with current water use under current supply and demand network. The water sources are groundwater and the river channel. –Run under different crop rotation systems: –i) paddy-paddy ii) paddy- pulses (representing a low water intensity crop) iii) sugarcane –Simulations with and without environmental flow requirements/demands Scenario 2: With the Polavaram reservoir and Link canal: water supply versus demand after the construction of the Polavaram project. The water source is the Polavaram reservoir and link canal, ground water and the river channel. –Run under different crop rotation systems: –i) paddy-paddy ii) paddy- pulses (representing a low water intensity crop) iii) sugarcane –Simulations with and without environmental flow requirements/demands
9 3. Defining Supplies and Demands Water Supply Water source for the sub-catchments (RBC) are precipitation, surface water and groundwater. Water source for demands outside of the RBC are linked only to surface water In Scenario 1, Surface water is from the river flows In Scenario 2, Surface water is from the rivers, the Polavaram reservoir and link canal In Both Scenario 1 and 2, Ground water is represented by a node and the total availability and natural recharge was set based on Andrapradesh state government ground water reports
10 3. Defining Supplies and Demands Water Demand 1. Agriculture Within the sub-catchments, the FAO method was used to calculate crop requirements Annual water demands from the government reports were used to set demands from the Prakasham Barrage, Author Cotton Barrage and Left bank demand 2. Urban and Rural Domestic water use Mandal and District Level data NWDA feasability report 3. Industry Calculated from district wise industrial output 4. Livestock District Level data NWDA feasability report
11 Environmental Flows Requirements The environmental water demands (environmental flows requirements) were estimated using the desktop method which is based on the use of a flow duration curve – a cumulative distribution function of monthly flow time series (Smakhtin and Anputhas 2006). The environmental flows calculated for the lowest acceptable category D (‘largely modified’ rivers) were used in this analysis.
12 Results: Scenario 1(Current Water Use) Total Unmet Demand Figure 1 shows monthly average (1991-2004) unmet demands from agriculture, domestic use, industry and livestock for the sub-watershed falling under the link command area for different cropping patterns and with inclusion of environmental flows. All cases include conjunctive surface and ground water use. The highest unmet demands are for the paddy- paddy with e-flows and lowest for paddy-pulses Unmet demands are in all months Figure 2. Scenario 1: monthly average (1991- 2004) unmet demands based on water requirements from Author Cotton barrage and the Polavaram left bank canal area The unmet demands from the left bank and Arthur Cotton barrage are during the Rabi and dry seasons and are probably being met by groundwater Figure 1. Monthly average unmet demands for the link command area Figure 2. Monthly average unmet demands for Arthur Cotton and left Bank
13 Results: Scenario 2 (Polavaram Project) Total Unmet Demand Figure 3 shows monthly average (1991- 2005) unmet water demands under paddy- paddy crop rotation. Unmet demands in the link command area are minimal compared to those in Author Cotton area and left bank. Within the link command area, the water deficit situation improves from the current situation however, if environmental flows requirements are set, then there is a small deficit in the link command area under paddy- paddy cropping system Compared to the current situation, the pressure on water resources within the left and right bank command area reduces, however, there will be increased deficit in the Author cotton command area. This deficit is during the Rabi and summer seasons. Figure3. monthly average (1991- 2005) unmet water demands under paddy- paddy crop rotation Figure 4. monthly average (1991- 2004) unmet demand for the link command area
14 Results: Scenario 2 (Polavaram Project) Reservoir Storage Volume Jun 1991 Jan 1992 Sep 1992 May 1993 Jan 1994 Sep 1994 May 1995 Jan 1996 Sep 1996 May 1997 Jan 1998 Sep 1998 May 1999 Jan 2000 Sep 2000 May 2001 Jan 2002 Sep 2002 May 2003 Jan 2004 5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 Million Cubic Meters Salient features from the government feasibility report was used to simulate the reservoir. The published monthly net evaporation was used to calculate evaporation losses. The reservoir reaches the inactive zone (3,381 MCM) during every dry season which means that the water stored during each monsoon season will be utilized during the dry season of that same year. The reservoir storage capacity does not provide storage and ensure water for inter- annual variations.
Results: Environmental Flows Requirements Figure 6. Class D flow requirements plotted against measured flow from the gauging station at Vijayawada. Figure 7. Scenario 2: unmet environmental demand for Godawari under paddy-paddy cropping pattern
16 Conclusions The simulations suggest that the proposed Polavaram reservoir and link canal will reduce the pressure on water for the proposed command area of the reservoir. However, this will result in increased water deficits during Rabi and summer months in the lower Godawari Delta, which is being supplied through the Author Cotton barrage. Changing cropping patterns e.g. by planting paddy during the monsoon and a low water intensive crop such as pulses in the dry season in the link command area will decrease unmet demands for the lower Godawari Delta. However, this will not be enough to continue the present water use patterns in the Author Cotton command area. Similarly, the need to ensure environmental flows should also be considered in the context of seasonal variability, as it is mostly in the dry months that water allocation problems become critical. In the Godawari, it will not be possible to meet environmental flows requirements in June, just before the start of the monsoon if the onset of the rainy season is delayed. Meeting environmental flows requirements in the Krishna is a bigger problem than in the Godawari and the situation is not likely to improve even after the Polavaram project, as most of the water that is being transferred will be used for en route irrigation. This study suggests that water resources management in the region has to be done on a seasonal basis by taking monthly variability into consideration.