4-14 4.4 Groundwater Development Plan Formulation of a Groundwater Development Plan Is Difficult Compared with Areas That Have T
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The Study on Rural Water Supply JICA in Mwanza and Mara Regions in the United Republic of Tanzania KOKUSAI KOGYO CO., LTD. 4.4 Groundwater Development Plan Formulation of a groundwater development plan is difficult compared with areas that have thick sands and gravel sedimentation as a stratum aquifer, especially along large rivers. The porous and permeable layer in the alluvial and tertiary deposits does exist only in limited areas. In addition to the geological point of view, the water quality is largely affected by the mineralization and sedimentation that occurs in areas which have the potential of dissolving toxic substances such as fluoride, NO3 and saline minerals. However, there are certain areas which provide safe and sustainable groundwater. Therefore, the villages close to the high potential area in reference with the water availability map have a higher possibility of developing groundwater sources. 4.4.1 Evaluation of Exploitable Amount of Groundwater The mass balance of groundwater recharge of 35 years (1970-2004) is shown in the following table. The water balance calculation was made both for general mass balance calculation and application of the Tank Model, and the results have been obtained from the Tank Model calculation result. The extraction of groundwater in each district is estimated in the following table. Table 4.4-1: Potential Volume of Groundwater Exploitation and Extraction **Potential ***Potential Total ****Planned *****Planned Persentage in Recharge to *Extractable Discharge of Discharge of Exploitation total the Explotable Hand Pump Motorized Pump from District Groundwater Groundwater Existing Hand Existing Motorized Amount Exploitation Exploitation Groundwater Region Pump Pump m^3/sec m^3/day m^3/day Number m^3/day Number m^3/day m^3/day m^3/day m^3/day % Missungwi 126.78 10,953,978 5476989 267 1922.4 59 1982.4 477 528 4909.8 0.0896441 Sengerema 147.16 12,714,442 6357221 205 1476 5 168 2195 312 4151 0.0652958 Kwimba 196.78 17,002,010 8501005 612 4406.4 18 604.8 1042 2016 8069.2 0.0949205 Magu 195.39 16,881,811 8440905 791 5695.2 42 1411.2 885 388 8379.4 0.0992713 Mwanza Geita 270.59 23,378,909 11689454 198 1425.6 49 1646.4 3233 416 6721 0.0574963 Ilemela-Nyamang 28.02 2,421,064 1210532 90 648 0 0 143 791 0.0653432 Ukerewe 93.52 8,080,247 4040123 268 1929.6 0 0 75 0 2004.6 0.0496173 Bunda 169.89 14,678,128 7339064 173 1245.6 3 100.8 795 70 2211.4 0.0301319 Musoma 189.38 16,362,690 8181345 60 432 6 201.6 2207 696 3536.6 0.0432276 Mara Tarime 221.08 19,101,607 9550804 16 115.2 7 235.2 7117 623 8090.4 0.0847091 Serengeti 733.38 63,364,255 31682128 52 374.4 8 268.8 1331 830 2804.2 0.008851 * Extractable Groundwater = Groundwater Recharge * 0.5 ** Assuming all wells have hand pumps with 15 l/min discharge operating 8 hours a day *** Assuming all wells have functioning motorized pumps with 70 l/min discharge operating 8 hours a day **** Planned hand pumps exploitation in the year 2015 ***** Planned motorized pumps exploitation in the year 2015 The total existing and planned volume for the exploitation of groundwater and the ratio (percentage) to the total recharge is less than 0.1 %. The highest percentage is in Magu District, which has only a small catchment area. Therefore, the amount of current and future (year of 2015) exploitation is still in reasonable proportion to the total volume of groundwater. However, from June to September (dry season), no potential recharge can be expected. It should be noted that even the medium and deep boreholes may experience a decline in the water level (not all of the deep wells, but some of the medium wells which are highly affected by seasonal fluctuations) in some cases. 4-14 The Study on Rural Water Supply JICA in Mwanza and Mara Regions in the United Republic of Tanzania KOKUSAI KOGYO CO., LTD. 4.4.2 Remarkable Points for the Groundwater Development Plan a. Groundwater Development Plan for 428 Villages The groundwater development plan was formulated for the 428 villages of the water supply plan, based on the natural conditions and surveys. From the location of the village, the following are interpreted from the potential area for groundwater development. • Aquifer Type • Estimated yield at the location of the village • Estimated well depth to the target aquifer The results are compiled in Figure 4.4-1. Formulation of the water supply plan, by comparison of the facility cost, the natural conditions and the available water sources, is described in the section on the Water Supply Plan. The groundwater development is relatively difficult, especially estimating the yield and the depth to the water strike zones. Therefore, for villages within 9 km of Lake Victoria, lake water will be used instead of groundwater. Most of the facilities for groundwater extraction are boreholes drilled up to 50 meters and installed with a hand pump (as the yield of the well is very difficult to predict, a motorized pump is not planned unless certain data is available to assure a yield of more than 70 l/m). There are risks to the groundwater development by means of yield, water level and water quality of the aquifer. However, utilizing the useful well information and the interpretation results, exploitation of the safe groundwater shall be possible by further detailed analysis and surveys. b. Groundwater Development Plan for the Priority Project. A total of 61 villages were surveyed in detail for the examination of the water development potential for groundwater source. The purpose of this detailed hydrogeological field reconnaissance is to identify the potential well site at each village within the village boundary. The method of the survey is outlined as follows (Location is shown in Figure 4.4-2) - Detailed hydrogeological field reconnaissance to identify the additional wells and springs to review the water source development potential in the village. - Interview the village leaders to locate most appropriate site for water source (about 6-8 points in the village). - Review respective points from the hydrogeological point of view with the rank of A (good), B (fair) and C (poor). - Additional recommended sites are marked on the topographical map in case that the requested site does not have good potential. The 61 copies of maps are attached in the Data Book for use in the implementation phase. 4-15 The Study on Rural Water Supply JICA in Mwanza and Mara Regions in the United Republic of Tanzania KOKUSAI KOGYO CO., LTD. Figure 4.4-1: Groundwater Development Plan Figure 4.4-1 4-16 The Study on Rural Water Supply JICA in Mwanza and Mara Regions in the United Republic of Tanzania KOKUSAI KOGYO CO., LTD. Figure 4.4-2: Target Village for Supplementary Hydrogeological Survey 4-17 Figure 4.4-2 The Study on Rural Water Supply JICA in Mwanza and Mara Regions in the United Republic of Tanzania KOKUSAI KOGYO CO., LTD. 4.5 Water Quality in Study Area Water quality analysis was conducted on groundwater and surface water (lake water, river water, pond water, dam water, etc.) to confirm the nature and safeness of the water for potable purposes. In addition to examination of the safety of the water, the quality was examined to determine whether there is a seasonal fluctuation during the year. 4.5.1 Methodology and Water Quality Items The water quality survey consists of water sampling at the site, and the laboratory tests. The sampling schedule was divided into four phases, I, II, III, IV, of which phase I and IV and phase II and III represent the analysis value in the wet and dry season respectively. The total number of the samples are 154, 68 samples taken in the dry season, 68 in the wet season and 18 samples from the test wells. The 14 parameters for on site water quality measurements are as follows: Temperature, electric conductivity (EC), pH, oxidation-reduction potential (ORP), Fe, Mn, F, - + NO3 , As, NH4 , coliform, general bacteria, taste and odour. In the laboratory, the following 40 parameters were analyzed for each sample: Coliform group, coliform (E.Coli or heat-resistant coliform bacteria), Pb, As, Se, Cr, Cn, Cd, - Ba, Hg, F, NO3 , color, turbidity, pH, total filterable residue (TFR), total dissolved solids 2- - (TDS), total hardness (as CaCO3), Ca, Mg, SO4 , Cl , Fe, Mn, Cu, Zn, BOD, Oxygen as + - + KMnO4, ammonia (NH3 + NH4 ), Bo, Ni, Mo, NO2 , residual chlorine, Na , water + - temperature, EC, K , HCO3 and Total Phosphorus (TP). Total Suspended Solids (TSS) was measured instead of TFR, as TFR and TDS indicate similar meaning values despite a different method of analysis. The parameters analyzed were considered from the drinking water standards of Tanzania with reference to WHO guideline, and major ions which may affect human health. 4.5.2 Characteristic of Water Quality The results of the water quality analysis in the field and laboratory in respective water sources are summarized as follows; detailed description of the water quality is attached in the supporting report. a. Characteristic of Water Quality by Water Source a.1 Well Deep wells are not so much affected by bacteria but they contain a series of metal ions such as Fe, Pb, Cr, Se, Ba and F. Looking at the Standards of Water Quality of Tanzania and WHO, some of the parameters exceed the allowable values. Granite fissure type aquifers in Kwimba and Magu indicated a high content of Fluoride.