SUSWA Knowledge ExchangeDecember 2014

Hydrogeological surveying

Collect and analyse existing sources of information:- Existing boreholes/wells (depth, yield, geology, water

quality, etc.)- Geological map + report- Topographic map- Google Earth

Formulate a hypothesis:- Where could you find water and what type of aquifer do you expect?- How deep do you expect to strike the water?

Hydrogeological surveying

Verify this hypothesis in the field:- Look around (topography, geology, soils- Make a profile (using your GPS measurements, or

based on Google Earth or maps)- Water point mapping: verify the GPS coordinates of

the nearby boreholes.

Be there when the drilling takes place:This is the only moment you can actually touch your aquifer!- See the different types of geology encountered while

drilling and at which levels they strike water.- Talk to the driller, ask him about drilling speed in the

water bearing layers etc etc- Learn from this for future boreholes.

Geophysics

There is no machine that tells you where to drill to find water and at what depth.

There are however several techniques that can improve your change of success:- Sounding- Profiling according to your sounding (to determine

electrode spacing)- Direction of the measurements according to the

geology- Other

Try to improve your concept together with your consultants using these techniques.

Geophysics

How to measure under difficult circumstances (very dry topsoil):- Use long (1 m) electrodes- Use stainless steel potential electrodes- Add salt water around the electrodes- Increase the number of current electrodes- Take a Wenner sounding instead of Schlumberger

You can help your consultant by giving him this information!

Geophysics

After drilling:Go back to your concept and verify your interpretation (hydrogeology, topography, geophysics) and write down your conclusion in a report.

Learn from this for future projects!

What should you demand from your consultant?

In the TOR ask for:- Note in the report the GPS coordinates + directions

of all geophysical measurements.- Note down the brand, type and serial number of the

instrument used.- Note down which interpretation software has been

used for interpreting the geophysical measurements.- A map showing: the locations of nearby boreholes,

locations + directions of measurements, recommended site for drilling.

- Present all VESses in 1 chart to allow good comparison.

- Give the concept of which type of aquifer is to be expected and at what depth you could strike water.

What should you do after field surveying?

Store all information for each borehole (also the dry ones!) in your office and digitally:- Location- Hydrogeological/Geophysical survey report- Borehole completion record- Drillers log- Test pumping- Water quality- Other observations of interest

This information can help you (and your consultant) when you want to start a nearby project.

Be there when the drilling takes place.

Water point mapping

Introduce a standard format to store information on boreholes:- Use this to store and share information- This can be very valuable for future water projects- And this can help if quick interventions are required

If you do this with all organisations within the Kenya WASH Alliance this can be beneficial for all.

Sustainability

Are our boreholes sustainable?- How much water are we extracting and how much

water is being recharged?- Are the waterlevels in the boreholes declining?

Safe yield is not the same as sustainable yield!We might be mining our groundwater.In the long term this can cause many problems (dry boreholes, deeper and deeper boreholes, higher cost, more failed drillings, more expensive pumps required, etc.)

Understanding the hydrogeological concept and monitoring of water levels is essential to understand if what we are doing is sustainable.

Increasing the recharge and other water sources (3R) might be necessary to create a sustainable system.