CGWB - Publications and Media Warehouse
Category | Artificial Recharge |
---|---|
State | All |
District | All |
Block | All |
Year of Issue | 2021 |
Number of Authors | 1 |
Name of Authors | CGWB |
Keywords | Scope, Purpose, Types of Artificial Recharge structures, Impacts, Methodology for impact assessment, Preparation of Reports |
File | Download |
Artificial recharge to ground water is defined as the recharge that occurs when the natural pattern of recharge is deliberately modified to increase recharge (ASCE 2001). In other words, artificial recharge to groundwater indicates the process of augmenting the recharge to groundwater exceeding the natural condition of replenishment through man-made interventions. Groundwater extraction to meet the increasing demands of fresh water has resulted in deepening of water levels and consequent impacts include drying of shallow aquifers, deepening of wells and increasing pumping costs. Augmenting recharge is normally taken up as a supply side measure to make the groundwater system sustainable. Based on the terrain conditions and availability of surplus source water, suitable artificial recharge structures are selected and designed to suit local conditions to make them effective. Impact of artificial recharge/water conservation structures constructed for augmenting/ conserving water on the prevailing ground water regime/ environment may vary widely. Realistic assessment of impacts of these interventions are necessary to assess the efficacy and cost-effectiveness of the structures for planning future interventions Groundwater being a hidden resource and a dynamic system in which recharge and extraction take place simultaneously at multiple points, indirect indicators are often made use of to understand the impacts, in addition to the direct indicators. The purpose of this document is to suggest broad guidelines on the methodology of impact assessment studies, so as to make a common protocol for use by the stakeholders. The types of artificial recharge structures depend primarily on terrain conditions. In case of water spreading methods, structures like gully plugs, nalah bunds, percolation ponds etc. can facilitate augmented infiltration, whereas in case of presence of impermeable layers between aquifer and the surface, the structure has to penetrate the impermeable layer to facilitate the movement of water into aquifer. Structures such as recharge shafts, recharge wells etc. could be the suitable in such cases. In case of recharge of confined aquifers, water may have to be injected into the aquifer system under pressure to facilitate recharge. The impact of any artificial recharge structure/scheme can be either direct or indirect impacts as listed- Direct Impacts o Rise in water level – Arresting of Declining water level (rate/absolute Value) o Increase in cropped Area – Increase in the area cultivated with water intensive crops or with the existing cropping pattern o Increase in yield of wells – Wells sustain pumping during lean months and pumping hours reduced for the same command area, Increase in pumping hours – Longer duration of pumping or increase in number of pumping days. Maintenance of water level/yield of wells/command area during years of deficit rainfall, Improvement in Quality – Improvement in ground water quality due to dilution effect (changes in concentrations of dissolved ions, individually or collectively). Indirect Impacts o Increase in vegetation cover in surrounding areas o Increase in non-seasonal flow in the streams/ rivers o Less frequent development of cracks in soil due to increased soil moisture. The impact assessment should commence prior to initiation of construction of artificial recharge structures and should ideally continue for at least two water years after construction. The study should be inclusive of direct and indirect parameters indicating the impacts. In general, the area of influence of a single structure could be taken as 1 sq.km on the downstream side and depending on the flow direction, the impact will be pronounced. Methodology for Impact Assessment as data Collection, Method of Analysis, Groundwater Extraction Analysis, Water Quality Analysis, Tracer Analysis, Isotope Analysis, Water Balance Study Preparation of Reports as a generalized layout for the report is suggested for the impact assessment study of Artificial Recharge Projects (Introduction, Background information, Area Details, Climate/Rainfall, Hydrogeology, Need for Artificial Recharge, Methodology adopted for Impact Assessment, Data Analysis and Inferences, Source of Data).