Status: U Date: Sat, 28 Feb 2004 11:11:56 +0000 (GMT) From: Jagadiswara R <[EMAIL PROTECTED]> Subject: Will subsurface dams deprive the downstream users their fair share of water?, Will subsurface dams deprive the downstream users their fair share of water? To: [EMAIL PROTECTED], [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] MIME-Version: 1.0
Content-Type: text/plain Content-Transfer-Encoding: 8bit Content-Id: Content-Disposition: inline Greetings Mr. Chan: Thanks for your mail (Message #1309). Despite living essentially in upstream, I appreciate your concern for downstream users. My reply to your question that subsurface dams might deprive downstream users the fair share of water in already water-scarce regions is as follows. I will mail the answers for your remaining questions in due course. The utility of subsurface dams can be best understood by observing how ephemeral streams become perennial while flowing through gorge portions, which can be treated as naturally-formed subsurface dams. Owing to the occurrence of sandy formation with large width and thickness beneath the streams both before entering a gorge and after leaving it, they remain mostly dry during lean season and thus present the characteristics of losing streams. The width and thickness of sandy formation beneath the gorge is so low that a good portion of groundwater emerges to surface as base flow to present characteristics of gaining streams. Although dams were constructed across many such gorge portions to submerge valuable land, the opposition by the upstream users has allowed many such gorge portions left untouched. Let me describe one such gorge in the Papaghni river of Pennar basin in Cuddapah (Kadapa) district in Andhra Pradesh through pictures. Picture 1 shows the gorge portion of the river at a place called Gandi, where the river shows the characteristics of gaining and losing streams even on a local scale, thereby reflecting changes in the subsurface storage of shallow groundwater. Picture 2 on the other hand shows the surface runoff in the main gorge portion of the river for good portion of the year, while picture 3 shows how a portion of that water is diverted through a 3-km long supply channel to flow by gravity to irrigate 121 ha of downstream land. Although many spring channels along the river at other locations have dried owing to groundwater exploitation in the riverbed, this spring channel is still able to provide irrigation water even now. Groundwater occurs a few centimetres below the bed level during summer in portions of the river bed both in the upstream and downstream of the gorge for growing water melons on the riverbed through subsurface irrigation (Picture 4). Farmers whose lands don�t get supply channel water have constructed low-cost shallow tube wells (called locally filter points) in the riverbed with indigenous technology to lift water with centrifugal pumps. Figure 5 shows one such shallow tube well of a farmer with provision to pump well water into an erect hollow pipe so that his 10-acre land adjacent to the river but located at higher elevation could be irrigated round the year by gravity flow from an underground pipeline. Unlike the small extent of land irrigated by the supply channel, groundwater development through low-cost wells has allowed for irrigating several hundreds of acres of land of small farmers. It is so convenient to pump groundwater rather than depend on the supply channel, requiring community effort for maintenance, even the farmers depending on the supply channel found it more convenient to go in for their own source of groundwater. Suppose a subsurface dam is constructed across the river in the gorge portion, the additional groundwater arrested can provide additional water for irrigating more land. The additional groundwater so arrested could be used through low-cost wells upstream of the subsurface dam for use by both upstream and downstream users through an equitable formula arrived by consensus. In the absence of the construction of the subsurface dam, the water flows in the river at such great depth that it cannot be exploited through low-cost shallow wells in the downstream. As the lands far away from the gorge portion both in the upstream and downstream cannot anyway hope to develop shallow groundwater through low-cost wells, they have to meet their water needs through deep bore wells fitted with deep-wells pumps. As both the downstream and upstream users live in the same country, international treaties should not obstruct for the construction of a subsurface dam at this gorge portion for the benefit of more number of farmers. Regards, Rao P.S. The attachment to this message has both text and pictures. I can mail the attachment to any forum participant requiring it ([EMAIL PROTECTED])., Greetings Mr. Chan: Thanks for your mail (Message #1309). Despite living essentially in upstream, I appreciate your concern for downstream users. My reply to your question that subsurface dams might deprive downstream users the fair share of water in already water-scarce regions is as follows. I will mail the answers for your remaining questions in due course. The utility of subsurface dams can be best understood by observing how ephemeral streams become perennial while flowing through gorge portions, which can be treated as naturally-formed subsurface dams. Owing to the occurrence of sandy formation with large width and thickness beneath the streams both before entering a gorge and after leaving it, they remain mostly dry during lean season and thus present the characteristics of losing streams. The width and thickness of sandy formation beneath the gorge is so low that a good portion of groundwater emerges to surface as base flow to present characteristics of gaining streams. Although dams were constructed across many such gorge portions to submerge valuable land, the opposition by the upstream users has allowed many such gorge portions left untouched. Let me describe one such gorge in the Papaghni river of Pennar basin in Cuddapah (Kadapa) district in Andhra Pradesh through pictures. Picture 1 shows the gorge portion of the river at a place called Gandi, where the river shows the characteristics of gaining and losing streams even on a local scale, thereby reflecting changes in the subsurface storage of shallow groundwater. Picture 2 on the other hand shows the surface runoff in the main gorge portion of the river for good portion of the year, while picture 3 shows how a portion of that water is diverted through a 3-km long supply channel to flow by gravity to irrigate 121 ha of downstream land. Although many spring channels along the river at other locations have dried owing to groundwater exploitation in the riverbed, this spring channel is still able to provide irrigation water even now. Groundwater occurs a few centimetres below the bed level during summer in portions of the river bed both in the upstream and downstream of the gorge for growing water melons on the riverbed through subsurface irrigation (Picture 4). Farmers whose lands don�t get supply channel water have constructed low-cost shallow tube wells (called locally filter points) in the riverbed with indigenous technology to lift water with centrifugal pumps. Figure 5 shows one such shallow tube well of a farmer with provision to pump well water into an erect hollow pipe so that his 10-acre land adjacent to the river but located at higher elevation could be irrigated round the year by gravity flow from an underground pipeline. Unlike the small extent of land irrigated by the supply channel, groundwater development through low-cost wells has allowed for irrigating several hundreds of acres of land of small farmers. It is so convenient to pump groundwater rather than depend on the supply channel, requiring community effort for maintenance, even the farmers depending on the supply channel found it more convenient to go in for their own source of groundwater. Suppose a subsurface dam is constructed across the river in the gorge portion, the additional groundwater arrested can provide additional water for irrigating more land. The additional groundwater so arrested could be used through low-cost wells upstream of the subsurface dam for use by both upstream and downstream users through an equitable formula arrived by consensus. In the absence of the construction of the subsurface dam, the water flows in the river at such great depth that it cannot be exploited through low-cost shallow wells in the downstream. As the lands far away from the gorge portion both in the upstream and downstream cannot anyway hope to develop shallow groundwater through low-cost wells, they have to meet their water needs through deep bore wells fitted with deep-wells pumps. As both the downstream and upstream users live in the same country, international treaties should not obstruct for the construction of a subsurface dam at this gorge portion for the benefit of more number of farmers. Regards, Rao P.S. The attachment to this message has both text and pictures. I can mail the attachment to any forum participant requiring it ([EMAIL PROTECTED]). ________________________________________________________________________ Yahoo! India Insurance Special: Be informed on the best policies, services, tools and more. Go to: http://in.insurance.yahoo.com/licspecial/index.html Content-Type: application/msword; name="SSDams.doc" Content-Description: SSDams.doc Content-Disposition: attachment; filename="SSDams.doc" _______________________________________________ Assam mailing list [EMAIL PROTECTED] http://pikespeak.uccs.edu/mailman/listinfo/assam To unsubscribe or change options: http://pikespeak.uccs.edu/mailman/options/assam
