ARTIFICIAL GROUND WATER RECHARGE FIELD STUDY : SITE CHARACTERIZATION AND TEST RESULTS

Research Article ARTIFICIAL GROUND WATER RECHARGE FIELD STUDY : SITE CHARACTERIZATION AND TEST RESULTS 1 Prof. Pratima Patel, 2 Dr. M. D. Desai Address for correspondence 1 Ph.D Research Scholar SVNIT, Surat & Asst. Prof. Civil Engineering Department, Sarvajanik College of Engineering & Technology, Athwalines, Surat-395001, Gujarat, India, E-mail pratima13p@gmail.com 2 Ex. Prof. & Head, Applied Mechanics Department, S. V. National Institute of Technology, Surat-395007, Gujarat, India, ABSTRACT Over-exploitation of local ground-water resources can be prevented by inducing ground-water mounding through artificial recharge using rain water stored in specially constructed basins. In order to maintain the regional water balance and to assure optimal use of available water, knowledge of the water-table fluctuation in response to the proposed recharged scheme is essential. In this paper suitability of the site criteria for recharge bore well is discussed. Also focused on collection of surrounding site geotechnical data, topography of the site, geometrical parameters, evaluation of aquifer, and mathematics of ground water. Mathematical modelling of ground water flow related to unconfined aquifer with a change in saturated thickness with variation in Piezometric level, permeability, radius of influences or distance between two recharge well and presence of recharge by rainfall is discussed here. By using quadratic mathematical expression some significant relationship can be established. Drawdown and detention time of water storage can also be determined. The technique is implemented to an unconfined aquifer with horizontal impervious base receiving vertical recharge using rain water stored in specially designed basin. Authors have set up precast octagonal recharge well system at proposed site and suggested design parameters for roof top rain water recharge system. Recharging capacity of well can be evaluated by field test and confirmed with analytical solution. Authors have established correlations between radius of bore well r and depth of pervious strata h with capacity of borehole Q r which are adopted at site and gives satisfactory results, few are highlighted. KEYWORDS: unconfined aquifer, artificial recharges techniques, geometrical parameters, radius of influence, draw down, Hypothesis of Water. INTRODUCTION Human health and welfare, food security, industrial development and the ecosystems on which they depend, are all at risk, unless water and land resources are managed more effectively in the present decade and beyond. About one-fifth of the world s population lacks access to safe drinking water and with the present consumption patterns; two out of every three persons on the earth would live in water-stressed conditions

by 2025. With the growing demand of water, recharging of aquifer is fulfilled the need of the water crisis for future generation. Water is one of the renewable resources. India with an average rainfall of 1150 mm is the second wettest country in the world with good water resources. But the water resources are not evenly distributed over the country due to varied Hydro geological conditions and high variations in precipitation both in time and space. As large quantities of rainfall are going to sea as runoff, it is better to harness this wasteful runoff by adopting proper scientific conservation measures and constructing suitable recharge structures at appropriate locations and artificially recharge the depleted aquifers through recharge bore wells. Added would be the tremendous pressure to meet water requirements for other purposes such as for industrial use, environment and ecological management etc. emanating from population growth, the land use policies, degradation of water resources and depletion of aquifers in the country. [2] RESEARCHERS VIEW The problem of ground-water mound formation below artificial recharge basins has been investigated by many researchers-baumann (1952) Glover (1960) Davis S. N. and Dewiest R. J. M. (1966) highlight the methods of recharging of various aquifers. Hantush (1967) Hunt (1971) Bear J. (1979) Warner et al. (1989), Bouwer H. (1989) system for artificial recharge of aquifer Basak (1982) has presented closed-form analytical solutions of the Boussinesq equation for mound build-up and depletion in an island aquifer in response to constant recharge and evaporation over the entire aquifer. The water table at the boundary of the aquifer is assumed invariant with time. Zomorodi (1991) has shown solutions For different onedimensional and two dimensional flow models, Rai and Singh (1981, 1995) and Rai et al. (1994) have also shown that variations in the rate of recharge have significant effects on the growth of ground water mounds. Todd D.K. (2006) illustrates how the recharging of aquifer stops the salt water intrusion. I.S 15792 (2008) Artificial Recharge to Ground Water Guidelines mention the various methodology installed at various site. Design criteria for installing recharge system are not highlighted. So at present design procedure, system erection method & implementation of artificial recharge system is a today s prime need.

Table 1: Location of G.W.L Year Water level 1970 10 m below G. L. 1999 30 m - 60 m below G. L. 2050 80 m - 200 m below G. L. If not recharged now Table 2: Depth of Sand below Water Table located surrounding Project Site. Name of Site Depth of Sand Strata (m) Depth of Water Table (m) New Court Building 30 6 Tapi river - Amroli 30 6 Essar Hazira 30 5 Weir cum Cause way 24 8 Kribhco Jetty 35 6 Parle point 30 10 Puna Octroi Naka 20 10 Athwalines 21 16 Adajan 15 10 Ring road, station 32 20 V.N.S.G.U. 60 10 Varachha Bridge 25 13 SVNIT 35 6 Vesu ONGC 20 15 Table 3: Characteristics of Aquifer Materials Material Porosity n Specific yield % Sy Permeability k m/sec Clay 0.45-0.55 01-10 10-10 to10-6 Sand 0.35-0.40 10-30 10-5 to 10-3 Gravel 0.30-0.40 15-30 10-4 to 10-3 Sandstone 0.10-0.20 05-15 10-11 to 10-8

POPULATION, WATER NEED AND WATER AVAILABILITY [8] The population of India is estimated to reach a figure between 1.5 billion and 1.8 billion by the year 2050. The UN agencies have put the figure 1.64 billion. It is now generally accepted that the countries with annual per-capita water availability of less than 1,700 m 3 are water stressed and less than 1000 m3 as water scarce. India would therefore need 2,788 billion cubic meters (b.c.m.) of water annually by 2050 to be above water stress zone and 1650 b.c.m. to avoid being water scarce country. The average annual surface water flows in India has been estimated as 1869 b.c.m. of which 690 b.c.m. only can be utilized. If appropriate storage techniques can be created than maximum water can be store. The demand of water is increasing day-byday resulting in extraction of more and more groundwater and such extraction is in far excess of net average recharge from natural sources and hence it necessitates artificially recharging the aquifers to balance the output. Hypothesis of water available In year 1970, water was freely available. In year 1980, 50 paisa/glass. In year 1999 12 Rs./liter. In year 2050, may be 100 Rs./liter. [6] Thus, there is immediate need to conserve every source of usable water for the future generation. Planning and management of 10 years could post pone water crisis by few more years. Ground Water Level in Past Tweenty Years Data are shown in Table 1 Table 4: Coefficient of Permeability for Various Sands (USBR Earth manual, I.S. Code 1498) Type of Sand Particle size Permeability k (m/sec) Sandy silt < 75 micron 2 x 10-6 Silty sand < 75 micron 5 x 10-5 Very fine sand 425 micron 2 x 10-4 Fine sand 425 micron 75 micron 5 x 10-4 Fine to medium sand 2 mm 425 micron 1 x 10-3 Medium to coarse sand < 4.75 mm 2 x 10-3 Coarse sand and gravel 20 mm 4.75 mm 5 x 10-3

LOCATION OF PROJECT SITE & SITE CHARACTERIZATION It reflects a detail of soil stratification 17 m depth of bore log soil classification & its properties, depth of water table, depth of pervious strata, and type of soil exist at bed level. This exercise is required for identification of soil aquifer.also shows Ground water level found at 11m from G.L below this medium to coarse sand available which is suitable for recharging system. (Figure1). Figure 1: Project Site AMD, SVNIT, SURAT Bore log Soil Stratification with recharge well Figure 2: Map of Surat City (Project site)

EVALUATION OF SOIL AQUIFER W.R.T. EXPLORATION DATA (Figure 2 & Table 2). Referring to geotechnical exploration data of SVNIT project site and its surrounding region following observations are made: Up to 25-30 m depth sand strata (SW-SM-SC-GM) available below G.W.L. and below this depth highly impervious soil strata (MH-CH-CI) exists. A soil stratum below the well casing is greater or equal to five times diameter of bore well. Depth of pervious soil strata 5 x d or (10 x r) Water table = 11.4 m. Sand strata available in general below G.W.L. up to 25 m Pervious Strata available at this site is 25 11 = 14 m. 14 m 5 x 0.15 i.e. 14 m 0.75 m Above remarks fulfil the criteria of unconfined aquifer so recharge problem can be design and analyze under the UNCONFINED AQUIFER category. Figure 3:One-dimensional flow in an unconfined aquifer above an impervious base Figure 4: Artificial Recharge by Fully Penetrating Recharge Wells in an Unconfined Aquifer above an impervious base

Figure 5: Schematic lay-out of installation of precast octagonal step well Figure 6: Recharge well with open bottom

GEOMATRICAL PROPERTIES OF UNCONFINED AQUIFER For designing any type of recharge system geometrical properties of an unconfined aquifer is required. Storage function of aquifer material is depending on: porosity, specific yield, retention, storage coefficient, transmissibility, permittivity & permeability. (i) Porosity (n) It is the ratio of the volume of voids (pores) in soil mass to its total volume. Coarse to medium sand : 0.26to 0.42 Fine Sand : 0.3 to 0.4 Sandy Gravel : 0.2 to 0.35 Uniformly graded sand has a higher porosity than coarse sand. (ii) Storage Co-Efficient It is defined as the volume of water released (or stored) by an aquifer per unit surface area. In an unconfined aquifer, it corresponds to its specific yield. For unconfined aquifers it range from 0.02 to 0.3 The actual values can be obtained from the pumping out test. (iii) Specific Retention (Sr) It is ratio of the water retained to the volume of aquifer. It depends on grain size, shape, distribution of pores and compaction of the soil formation. For sand 10 to 30%, For sandy Gravel 10 to 80%, n = Sy + Sr (Table 3). (iv) Specific Yield (Sy) The volume of water, expressed as a percentage of the total volume of saturated aquifer, that can be drained by gravity is called the specific yield. Sand = 10% to 30% Sandy Gravel = 15% to 25% For unconfined aquifer Sy = 0.01 to 0.3 Specific yield depends upon - grain size, shape and distribution of pores and compaction of the formation. (v) Permeability (k) It is the ability of a formation to transmit water through its pores when subjected to a difference in water head. It has dimension of velocity (m/sec). It is the rate of flow per unit cross sectional area under unit hydraulic gradient. (Table 4) (vi) Transmissibility (T) It is the discharge through unit width of aquifer for the fully saturated depth under unit hydraulic gradient. T is directly varies with permeability and saturated thickness of the aquifer.

T = k b (m 2 /sec) For unconfined aquifer T = k b a (m 2 /sec) b a = average saturated thickness = (H + h) / 2 H=height of original water table,h= height of water in well after drawdown. (vii) PERMITTIVITY (Ψ): The ratio of permeability of soil (k) to thickness of soil sample (dx) is known as permittivity, measured in (sec) -1. It is preferred measure of water flow capacity across the soil mass. Ψ = k/dx r(m) h(m) Table 5: Q r = 15 x r x h 8m 10m 16m 18m 20m Q r m 3 /hr 0.05 6 7.5 12 13.5 15 0.075 (SVNIT) 9 11.25 18 20.25 22.5 0.10 (Panas) 12 15 24 27 30 0.125 15 18.75 30 33.75 37.5 0.15 18 22.5 36 40.5 45 0.30 36 45 72 81 90 k(m/hr) Table 6: Q r = 65 x d x k Fine Sand Coarse Sand (0.36 m/hr) (3.6 m/hr) More Coarser Sand (3.96 m/hr) d(m) 0.15 (SVNIT) 3.5 35 38.61 m 3 /hr m 3 /hr m 3 /hr 0.25 5.85 58.5 64.31 0.30 7.0 70 77.22 0.60 14.0 140 154.4 0.90 21.0 210 231.7

MATHEMATICS OF GROUND WATER FLOW-- UNCONFINED AQUIFER The flow of phreatic water in an unconfined aquifer above an impervious base is complicated by two factors: a change in the saturated thickness accompanying the variation in Piezometric level and the presence of recharge by rainfall. [3] (Figure 3) With the notation of Figure. 3 the equations of flow becomes Darcy Continuity dh q= kh dx dq = dx Integrated q = Px+ C1.(i) Put value of q in Eq.(i)kh dh/dx= Px+ C 1 Combined Integrated Px+ C hdh= 1 dx k 2 2 1 h x + P P 2C = x C2.(ii) k k In which the integration constants must be calculated from the boundary conditions. (Figure 4) For the recharge scheme of Figure 4 again consisting of three wells fully penetrating the saturated thickness of the aquifer, this boundary condition gives x = 0 2 2 h = h n = C 2 It means that height of water table and water mound is at same level Put x = 0 in Eq. (i) q = q 0 = C 1 From which follows Put x = maximum L, and values of C 1, C 2, in Eq. (ii) we get 2 P 2 2q0 2 h 0 = L + L+ h n..(1) k k By the quadratic form of this equation, finding a formula for the drawdown s 0 h 0 h n =..(2) The design of an artificial recharge scheme is mainly governed by: the time, the water is meant to stay underground and the amount of water that can be stored in the aquifer. The design value of detention time (T) during underground flow determines the improvement in water quality. T days = p H L/ q.. 0 (3) The natural recharge by rainfall can be calculated by, q r = P x L (4)

ERRECTION OF RECHARGE WELL WITH PRECAST OCTAGONAL STEP WELL AT PROJECT SITE. Please refer figure 5 TEST RESULTS Evaluation of Recharging Capacity of Design Well Recharging capacity of Recharge bore well with step well system installed at site is evaluated as: 8000 liter water from the tanker takes 15 minutes to percolate in the soil strata through 0.15 m diameter & 15 m deep recharge bore well. Therefore, Recharging capacity of design well= 8000lit./15min=533lit./min.=32 m 3 / hr. The overall recharging capacity of installed recharge well at project site is 32 m 3 / hr. It shows that in one hour 32,000 lit. water store in recharge well without spill off. Correlation Between r, h and Qr. Correlations between radius of bore well (r) and depth of pervious strata (h) with capacity of borehole (Q r ) (Figure 6) Overall capacity of Borehole [1] Qr = k A i t Coarse sand permeability10-3 m/sec=(3.6 m/hr) Area of Borehole = 2πrh Hydraulic gradient i = h/l = 20/30 Time = 1 hr Q r = 3.6 x (2πrh) x h/l x 1 = 3.6 x (2πrh) x 0.67 x 1 Q r = 15 r h..(5) (Table 5) Estimation of Recharge Capacity w.r.t. d and k Flow q r by constant head recharge in borehole. q r = 2.75 x d x h x k [3] Where, d = diameter of bore (m) h = depth of strata above the G.W.L (m) = Maximum up to 25 m k = co-efficient of permeability (m/sec) q r = 2.75 x 25 x d x k q r = 65 x d x k..(6) (Table 6) Constant value of bore diameter, with decrease in permeability recharges capacity reduces to 10 times. If we required more recharge rate then provide larger diameter bore instead of installing two smaller diameter of bore. If the recharge systems extend in fine sand (semi pervious strata) (refer figure 1) then 10% recharge rate is added to the original system in coarse sand.

Confirmation of Test Results for q r = 30 m 3 /hr (Theoretically) SVNIT (SURAT, GUJARAT) Project q r = 32 m 3 /hr (In-situ pumping in Site recharge trial test) Verifying recharge rate of installed q r = 35 m 3 /hr (Design table 6) artificial recharge well system at SVNIT All three approaches give considerably by theoretical, experiment & design same value of recharge rate. So adopted table. [4] value of designed recharge rate is confirmed. Table 7: Recharged water Quality Analysis S. Parameters Before Recharge One Year after Two Year No. Recharge after Recharge 1. Rise of G.W.L. 10.5 m 9.9 m 8.0 m 2. ph 8.2 6.8 7.5 3. Chloride mg/l 550 90 30 4. Hardness mg/l 399 200 200 Figure 7: Recharge bore well system at Panas, Surat

CASE STUDIES Recharge of groundwater through storm run off and roof top. Water collection, diversion and collection of run off into dry tanks, play grounds, parks and other vacant places are to be implemented by a recharge well. Authors have suggested (designed) different techniques at various sites which are listed below. Panas Recharge Bore Well: S.M.C., Surat. (Figure 7) Adopting 1.5 m depth and 12 m wide tank storage tank, 100 mm radius of P. V. C. pipe, 12m - 20m sloughed pipes and 20-22 cm Gravel pack [1] [9] Recharge rate Q r = 5.5 x r x h x k av = 5.5 x 0.1 x 18 x 10-3 = 35.6 m 3 /hr. This implies that recharging capacity of well is of 35.6 m 3 /hr.cosidering amount of recharge is 10 to 20 % of this means 35.6 x.2 = 28.48 m 3 /hr. Which is confirmed with value of design Table 5 ( 27 m 3 /hr ). Botanical Garden SMC, SURAT. Authors have given proposed design of artificial recharge well of 0.45m diameter & at 30m depth with bottom packed with gravel for development of garden connected with old bore well. Provide Geo filter at inlet pipe of drain. At top of tank RCC slab is constructed. 150 mm plain PVC pipe is installed as recharge well up to 30m depth of pervious coarse sand. (Figure 8, 9 & 10) Figure 8: 8 Cross Section of Bore Log at full depth at Botanical Garden SMC Surat Figure 9: 9 Plan & Section of proposed Ground Water Recharging System at Botanical Garden

Figure 10: Differential level Ground Water Recharging Scheme at Botanical S.V.R. College of Engg. & Tech, Surat. Ground Water Recharge Project: Technique adopted is Recharge Well & Bore.(Table 7 ) It show level of Groundwater is increases and quality of Groundwater is also improved after installing this technique. CONCLUSION Equation 5 gives design concept of recharge well with knowing actual value of depth of pervious strata for the proposed site. Table 5 directly gives relation of Q r with r and h. In other way, referring Table 5 if we required higher rate of recharge than installing one larger diameter well instead of two smaller diameter well which economies the project cost. Garden SMC, Surat Equation 6 shows recharge rate of well directly varies with d and k. Table 6 shows that with small variation in aquifer permeability, the recharge rate is drastically changed. If permeability of the aquifer is known than only proper diameter of well can be select from Table 6. From the equation 5 and 6 we can justify that for installing recharge bore well system permeability of soil, diameter of recharge well, depth of pervious strata are design governing parameters. REFERENCES [1] Alamsingh, 1975, Soil Engineering in Theory and Practice, Volume I Asia Publishing House, Bombay, pp.128-129. [2] Bear J., 1979, Hydraulics of Ground Water, McGraw-Hill, New York, pp.233-269. [3] Huisman L., T. N. Olsthoorn, 1983, Artificial Groundwater Recharge,

Pitman Advanced Publishing Program, London, pp. 33-79. [4] I.S.5529 Part I 1985, Indian Standard Code of Practice for In-situ Permeability Tests pp.6-12. [5] James W. Warner, David Molden, 1989, Mathematical Analysis of Artificial Recharge from Basins Water Resource, Bulletin 25, pp. 401-411. [6] Patel Pratima, Desai M. D., 2008, Analytical and Computational Aspect of Artificial Ground Water Recharging into Unconfined Aquifer, National Conference on Bitcon Durg, M.P. (India), pp. 16-19. [7] Patel Pratima, Desai M. D., 2009, Numerical Modelling and Mathematics of Ground Water Recharging -- Unconfined Aquifer, ACSGE International Conference BITS Pilani, Rajasthan. pp. 96 105. [8] Patel Pratima, Desai M. D., 2010, Artificial Recharge of Ground Water by Storm Water Reuse is Viable and Sustainable Solution for Better Tomorrow, 17 th IAHR-APD International Conference, AUCKLAND NEW ZEALAND Session: 6, Green Devices 3, Paper No.5. [9] USBR EARTH MANUAL PART I & II 1998, 3rd Edition Bureau of Reclamation. pp.541-546.