Recharge to Groundwater

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Let's discuss this issue;

How can we estimate the recharge rate to groundwater?

6 Answers

  2. Assignment of Land Use to Grids

    The area and percentage of each land use in each grid is assigned with specific Landuse.shp.

     

    Pipe Density for Foul, Potable and TSE Systems

    The progression in pipe density is calculated from the population projection. The first step involved manually identifying areas that are at, or close to, Build-Out conditions. The existing density of pipes and pipe length per grid is calculated from GIS layers of current data for foul, clean water and TSE models if available. If found in some grids that, road area is significant and is up to 10-15% of the grid area. Hence the pipe density for roads is an important component of the total pipe density in a grid and is also calculated from the existing pipe density data.

    The typical pipe densities are calculated for each land use by averaging the existing pipe density from grids with high development factor (build-out) and coverage of the land use.

     

    Samples data extracted from a project in Qatar and are used for arriving at these rates are as given below:

    • Single Family – Grids with single family land use > 50% and Development factor > 0.7
    • Multi Family - Grids with Multifamily land use > 35% and Development factor > 0.35
    • Mixed Land use - Grids with mixed land use > 35% and Development factor > 0.35 and pipe density greater than 10
    • Roads – Average rates for the three land uses were applied to road

    Increasing Trend in Population

    In case of some grids have no existing pipe density data and as a result the projected pipe density jumped unrealistically in value. In these grids the development rates are factored to distribute this sudden increase in pipe density for each decade as follows (using the 52 decade as an example):

    ((Development Factor in 52- Development Factor in 62)/ (Development Factor in 62 - Development Factor in 12))*[Pipe Density in 2062]

    Some grids can be found already at maximum capacity for pipes in certain year and hence have higher pipe density than the projected values. In these cases the smaller projected values are replaced by the existing values this particular year.

     

    Decreasing trend in Population

    It can be found that some grids have no existing pipes and a decreasing development trend. In these cases the pipe density is retained as 0. At the same time some grids have existing pipes and a decreasing trend in population due to a change in land use for mega projects, industrial development etc. Here the existing pipe density is retained and maintained constant for all the years.

  3. Greetings Everybody, continuing to investigate the methods of estimating the recharge to groundwater, I've worked on Building and Simulating a groundwater model using the GIS as follows;

    Building a Groundwater Model using GIS to estimate the Recharge:


    This approach records the process used to calculate the groundwater infiltration in the urban areas. The groundwater model will provide insights into the effectiveness and appropriate locations for groundwater drainage and water use strategies.


    The Groundwater Model should be simulated for the target protection year and urban recharge input files were thus calculated for the target year.


    Existing data sets are used to calculate the urban recharge and are calibrated against current water balance data. The development and change in urban recharge are then calculated for the target year.


    Core Data Sets:


    The data used to prepare each of the component groundwater infiltration input files is as follows:


    1. Project Boundary.
    2. Grid 1 km x 1 km, Cover 1km buffer area of boundary
    3. Shape Files of Landuse data.
    4. Shape Files of Road Data.
    5. Shape Files of Population Data.
    6. Shape Files of Sewer Data.
    7. Shape Files of Clean Water.
    8. Shape Files of TSE.
    9. Shape Files of Municipal Irrigation.
    10. Shape Files of Building.
    11. Shape Files of Parcel Data.
    12. Shape Files of Road Irrigation.
    13. Shape Files of Septic Tank.


    Preparation of Grid:


    The grid is prepared with a size of 1 km x 1 km area covering the Model Boundary with an extra 1 km buffer area around the peripheral edge. It must cover the entire area of study.


    The population data is assigned to each grid based on percentage area of Traffic Analysis Zones (TAZ).


    This is a methodology that has been previously developed and used within the Drainage Master Plan of Qatar. Each cell had the sum of the percentage of population of the TAZs which coincided with the grid as shown in the figure below.



    It is assumed that the population is spread equally across the entire area of the population TAZ boundaries. The development factor is based on the projected population growth and is prepared by identifying the peak year with the highest population which is assigned a value of 1 on the assumption that it will have maximum development.


    The remaining years are assigned a factor [Population of Year to be calculated]*1/ [Peak year Population]. So, for example, if 2062 has the highest population, 2012 will have a development factor = [Pop2012]*1/ [Pop2062]


    It will found that, there is increasing trends with peak population achieved. There are as well a few cases of decreasing trend in areas where significant industry developments or mega projects were planned for implementation.

  4. In this context, extensive field investigations were carried out by my team and me, for over four decades in different parts of India under semi-arid and arid conditions, using radioactive (3H, 14C, 234U, 238U) and stable (2H, 18O) isotopes. Mean recharge in river basins has been estimated using tritium injection technique by tracing soil moisture movement. Regional groundwater residence time in the aquifer and flow velocity has been estimated by 14C (T1/2 = 5730 yr) ages of groundwater. Groundwater seepage loss has been assessed using seasonal variation of 18O/16O and 234U/238U isotopic ratio and 238U concentration in groundwater and river water, representing varying components of overland and subsurface flow. 2H/1H and 18O/16O ratios have been used for detailed insight into the groundwater recharge and contamination characteristics, flow regime, flow-pathways and mixing in groundwater system. Potentials of isotope techniques based on my own four decades of experience provided a direct insight into the water dynamics and distribution within hidden groundwater aquifers system, and proved to be very useful for groundwater management.

  5. usually when talking about recharge into groundwater aquafires, we are encountered with the urban recharge which can be explained;

    Urban Recharge

    The use of water in metropolitan areas releases significant volumes of water indirectly from the urban infrastructure and directly from some water uses, such as parkland and garden irrigation.


    This water infiltrates into the superficial and shallow aquifer system, that together comprise a much greater contribution of recharge water to the aquifers in urban areas than the natural recharge from rainfall and run-off.


    The urban recharge contributions come from:

    • Natural recharge (direct recharge from rainfall)
    • Urban run-off (run-off from pavements, roads and roofs directed to infiltration basins, roadsides, soakways etc.)
    • Leakage from TSE and Drinking Water pressurized mains
    • Leakage or groundwater capture from the foul sewer network
    • Septic tank leakage (or groundwater capture from tank emptying)
    • Municipal and agricultural irrigation return
    • Domestic (garden irrigation return, car washing, etc.)

  6. Various methods and technologies are available to quantify ground water recharge, however, choosing appropriate techniques is sort of difficult. Important considerations in choosing a technique/method include space, time scales, range, soil conditions and reliability of recharge estimates based on different techniques.

    Methods for estimating recharge are subdivided into various types, on the basis of the 3 hydrologic sources , from which the data are obtained, namely surface water, unsaturated zone, and saturated zone.

    Water Budget is the most comenly used method. The water budget for a basin can be stated as:

    P + Q on = ET + Q off + Change in watre stogare

    where P is precipitation (and may also include irrigation); Qon and Qoff are water flow onto and off the site, respectively. ET is evapotranspiration.

    Lets discuss in deatil other methods as well. It would be good to know some new technologies like how GIS can be used for recharge mapping etc.

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