{"id":135,"date":"2020-11-18T16:03:22","date_gmt":"2020-11-18T16:03:22","guid":{"rendered":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/chapter\/estimating-the-recharge-rate-of-river-infiltration\/"},"modified":"2020-12-12T17:03:49","modified_gmt":"2020-12-12T17:03:49","slug":"estimating-the-recharge-rate-of-river-infiltration","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/chapter\/estimating-the-recharge-rate-of-river-infiltration\/","title":{"raw":"3.5 Estimating the Recharge Rate of River Infiltration","rendered":"3.5 Estimating the Recharge Rate of River Infiltration"},"content":{"raw":"Where groundwater recharge is dominated by infiltration from a river, groundwater beneath the river will be young, and groundwater further from the river will be older. The rate of river infiltration can be estimated by calculating the velocity of water flow away from the river, based on this increase in age.\r\n\r\nThe Danube River in Hungary (Figure 31) is a major recharge source for adjacent coarse-grained alluvial aquifers, and groundwater dating of these aquifers permits estimation of the rate of river infiltration. In this study, groundwater age was estimated using 3<\/sup>H\/3<\/sup>He dating. 4<\/sup>He and Ne data were used to estimate the recharge temperature and excess air, which was required to distinguish tritiogenic<\/em> 3<\/sup>He (3<\/sup>He derived from 3<\/sup>H decay) from 3<\/sup>He originating from other sources (i.e., atmospheric solubility and excess air components). Since the river dominates recharge to these aquifers, groundwater flow away from the river is essentially horizontal, and plots of groundwater age versus distance appear as straight lines (Figure 32), even though samples are collected from wells with long screens. Based on the rate of increase in age with distance, the groundwater velocity in shallow wells (screened 5 to 15 m below surface) is estimated to be approximately 800 m\/y, and in deeper wells (screened 50 to 100 m below surface) it is estimated to be approximately 530 m\/y.\r\n\r\n[caption id=\"attachment_186\" align=\"alignnone\" width=\"492\"]\"Map Figure <\/strong>31<\/strong> - Path of the Danube River in Eastern Europe (Wikimedia Commons, 2019).[\/caption]\r\n\r\n[caption id=\"attachment_188\" align=\"alignnone\" width=\"785\"]\"Figure Figure <\/strong>32<\/strong> - Estimated 3<\/sup>H\/3<\/sup>He age versus distance from the Danube River in Hungary, measured along the inferred groundwater flow path away from the river. Groundwater velocity appears to be greater in shallow wells (800 m\/y) than in deeper wells (530 m\/y) (From Cook and Solomon (2000), after Stute et al. (1997)).[\/caption]\r\n\r\nOne of the best examples of the application of this technique to ephemeral rivers (those that flow for only a short period during the year) is the study of the Finke River, central Australia (Fulton, 2012). Carbon-14 activities in groundwater show a general decrease with distance from the river, reflecting an increase in groundwater age (Figure 33). At distances beyond 40 km, 14<\/sup>C activities are less than 22 pmC, equivalent to groundwater ages of more than 12,000 years. At 20 km from the river, the mean 14<\/sup>C activity is approximately 60 pmC, equivalent to a groundwater age of approximately 4000 years. Assuming an age of zero at the river (distance of zero), this gives a mean velocity of 20 km in 4000 years, or 5 m\/y. Assuming an aquifer thickness of 200 m and porosity of 0.22, the author thus calculated mean recharge rates of 5\u00d7106<\/sup> to 12\u00d7106<\/sup> m3<\/sup>\/y for a 35 km reach of the river. This is equivalent to a recharge rate 0.71 m\/y, assuming a nominal river width of 200 m.\r\n\r\n[caption id=\"attachment_189\" align=\"alignnone\" width=\"1024\"]\"Carbon-14 Figure <\/strong>33<\/strong> - Carbon-14 activities in groundwater versus distance from the Finke River, central Australia. The location of the Finke River is shown in the left image (Wikimedia Commons, 2010. \u201cLake Eyre drainage basin including the major rivers<\/a>\u201d by Kmusser<\/a> is licensed under CC BY-SA 3.0<\/a>). The decrease in 14<\/sup>C activity re\ufb02ects an increase in residence time and was used to estimate the velocity of groundwater flow away from the river at 5 m\/y (After Fulton, 2012).[\/caption]","rendered":"

Where groundwater recharge is dominated by infiltration from a river, groundwater beneath the river will be young, and groundwater further from the river will be older. The rate of river infiltration can be estimated by calculating the velocity of water flow away from the river, based on this increase in age.<\/p>\n

The Danube River in Hungary (Figure 31) is a major recharge source for adjacent coarse-grained alluvial aquifers, and groundwater dating of these aquifers permits estimation of the rate of river infiltration. In this study, groundwater age was estimated using 3<\/sup>H\/3<\/sup>He dating. 4<\/sup>He and Ne data were used to estimate the recharge temperature and excess air, which was required to distinguish tritiogenic<\/em> 3<\/sup>He (3<\/sup>He derived from 3<\/sup>H decay) from 3<\/sup>He originating from other sources (i.e., atmospheric solubility and excess air components). Since the river dominates recharge to these aquifers, groundwater flow away from the river is essentially horizontal, and plots of groundwater age versus distance appear as straight lines (Figure 32), even though samples are collected from wells with long screens. Based on the rate of increase in age with distance, the groundwater velocity in shallow wells (screened 5 to 15 m below surface) is estimated to be approximately 800 m\/y, and in deeper wells (screened 50 to 100 m below surface) it is estimated to be approximately 530 m\/y.<\/p>\n

\"Map
Figure <\/strong>31<\/strong> – Path of the Danube River in Eastern Europe (Wikimedia Commons, 2019).<\/figcaption><\/figure>\n
\"Figure
Figure <\/strong>32<\/strong> – Estimated 3<\/sup>H\/3<\/sup>He age versus distance from the Danube River in Hungary, measured along the inferred groundwater flow path away from the river. Groundwater velocity appears to be greater in shallow wells (800 m\/y) than in deeper wells (530 m\/y) (From Cook and Solomon (2000), after Stute et al. (1997)).<\/figcaption><\/figure>\n

One of the best examples of the application of this technique to ephemeral rivers (those that flow for only a short period during the year) is the study of the Finke River, central Australia (Fulton, 2012). Carbon-14 activities in groundwater show a general decrease with distance from the river, reflecting an increase in groundwater age (Figure 33). At distances beyond 40 km, 14<\/sup>C activities are less than 22 pmC, equivalent to groundwater ages of more than 12,000 years. At 20 km from the river, the mean 14<\/sup>C activity is approximately 60 pmC, equivalent to a groundwater age of approximately 4000 years. Assuming an age of zero at the river (distance of zero), this gives a mean velocity of 20 km in 4000 years, or 5 m\/y. Assuming an aquifer thickness of 200 m and porosity of 0.22, the author thus calculated mean recharge rates of 5\u00d7106<\/sup> to 12\u00d7106<\/sup> m3<\/sup>\/y for a 35 km reach of the river. This is equivalent to a recharge rate 0.71 m\/y, assuming a nominal river width of 200 m.<\/p>\n

\"Carbon-14
Figure <\/strong>33<\/strong> – Carbon-14 activities in groundwater versus distance from the Finke River, central Australia. The location of the Finke River is shown in the left image (Wikimedia Commons, 2010. \u201cLake Eyre drainage basin including the major rivers<\/a>\u201d by Kmusser<\/a> is licensed under CC BY-SA 3.0<\/a>). The decrease in 14<\/sup>C activity re\ufb02ects an increase in residence time and was used to estimate the velocity of groundwater flow away from the river at 5 m\/y (After Fulton, 2012).<\/figcaption><\/figure>\n","protected":false},"author":1,"menu_order":5,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-135","chapter","type-chapter","status-publish","hentry"],"part":127,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/chapters\/135","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/wp\/v2\/users\/1"}],"version-history":[{"count":8,"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/chapters\/135\/revisions"}],"predecessor-version":[{"id":424,"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/chapters\/135\/revisions\/424"}],"part":[{"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/parts\/127"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/chapters\/135\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/wp\/v2\/media?parent=135"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/pressbooks\/v2\/chapter-type?post=135"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/wp\/v2\/contributor?post=135"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/introduction-to-isotopes-and-environmental-tracers-as-indicators-of-groundwater-flow\/wp-json\/wp\/v2\/license?post=135"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}