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Re:[gwmodel] Minimum permissible distance between bore holes in hard rock aquifers

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  • subrata halder
    To Dr. A.K. Ghosh Dear Sir, 1) Dr. BBS Singhal has used the ref of UNESCO 1972 for rad of Influence in fissured rocks.  2) In double porosity model, best
    Message 1 of 10 , Nov 12, 2012
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      To Dr. A.K. Ghosh

      Dear Sir,

      1) Dr. BBS Singhal has used the ref of UNESCO 1972 for rad of Influence in fissured rocks. 
      2) In double porosity model, best match with type curve has been achieved with porosity=10 %. Double porosity model is more representative of uniformly fractured aquifer. 
      3) Equations in connection with pumping Test are developed based on the assumptions of homogeneous & isotropic aquifers with laminar flow during pumping...well is 100% efficient and effective diameter is the same as the diameter of the well. But in reality aquifers are heterogeneous, anisotropic with non-laminar flow during pumping...pumping well is not 100% efficient and effective dia is usually more than dia. of screen mainly, in case of unconsolidated sediments. Considering the above reality, pumping well & observation wells are installed into closely spaced & inter-connected fractures and also, nested observation wells at different depth horizon in different direction are installed to get reading of water level at different depth & in different direction and an av. T value is computed. With a view to get  as much as radial,horizontal & laminar flow pattern, pumping well should be put in lower  1/2 or 1/3 rd of aquifer thickness and Observation
      wells should be located at dist. 1.5 times the saturated thickness of interconnected fractured aquifer. Considering the above reality, Huntley used the Specific Capacity(Q/Sw) as (Q/Sw)1.18and he modifed Thiem's Eq for fractured aquifer as T=A(Q/Sw)1.18   using the coefficient A=(2.3*log R/rw)/2π  (as in Thiem's Eq.) Thus Huntley's Eq holds good for  i) small dia 100% efficient pumping well and ii) nested observation wells in different & different direction installed in closely spaced interconnected fracture zone.  Therefore, I think earlier steps may be quite O.K. for finding out Rad of Influence (R).  
      4) Dr. BBS Singhal has not included the study of Anisotropic Aquifer Heterogeneous Aquifer with partial laminar flow and partial turbulent flow in his book. 
      Thanks
      Regards
      Subrata HalderExecutive Engineer (Agri-Irrigation)
      State Water Investigation Directorate
      Department of Water Resources Investigation & Development
      Govt. of West Bengal



      --- On Mon, 12/11/12, asokg@... <asokg@...> wrote:

      From: asokg@... <asokg@...>
      Subject: Re:[gwmodel] Minimum permissible distance between bore holes in hard rock aquifers
      To: "subrata halder" <shalder_2007@...>
      Date: Monday, 12 November, 2012, 9:54 AM

      Dear Subrata,


      Thank you for clarifying Hard Rock aquifer system so clearly. Do you

      have the details of reference UNESCO 1972. Was ir developed through

      observation or through some theoretical analysis?. If the original paper

      is available in soft I will like to have a copy of the same.Most of the

      equations in Step 1 are developed for Homogeneous isotropic aquifer. For

      double porosity I will like to know for what value(range) of porosity

      these equations are valid and what is the range of Reynold number for

      these porosity values. Huntleys equation is an Empirical Equation based

      on observation from field data. However, Huntley takes care of the

      turbulent flow part by introducing Specific Capacity ( S = AQ + BQ^n).

      Again in Step 3 we are using an Equation which is developed for Laminar

      Flow. Dr. Singhal has written a book of Hydrogeology of Fractured Rocks .

      I have not seen that book. I am sure you have gone through the book. I

      will like to know whether Dr. Singhal has included study of Anisotropic

      Aquifer Heterogeneous Aquifer with partial laminar flow and partial

      turbulent flow .
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