WATER AVAILABILITY

If you’re planning on growing anything, water is always the primary necessity. Its availability should be a key consideration in your decision to purchase. A reliable water source is mandatory.

When evaluating water access, you look at two things:

  • Existing water sources and their output
  • Water harvesting and storage potential

By diagnosing these two parameters you will be closer to an answer to the question of whether you’ll have enough water for your needs or not.

To perform this assessment, you’ll have to conduct an on-site investigation or at least some well-thought-out inquiries about the existing wells, springs, ponds, ditchwater, municipality water supply, etc. and the volumes of water they can provide. You’ll want to know exactly what’s there and how much water you can get…

The second part of assessing for the water harvesting potential includes analyzing the size of the watershed and the potential water storage locations.

This is principally performed online using Google Earth and topographic maps, and then confirmed on site. In our case, we’ll use the topography data we’ve already created for the terrain assessment.

    EXISTING WATER SOURCES AND THEIR OUTPUT

     

    STEP 1. Identify all the water sources on the property

    • Look around the property, does it have any running creeks/streams or springs?

    • Look for already built water tanks, dams/ponds and ditchwater.

    • Find out if there is a well that taps into the groundwater.

    • Find out if there is municipality water supply.

    STEP 2. Find out about the reliability of the water sources

    Having a water source and its level of reliability are two different things entirely. Find out how reliable the sources of water really are.

    • Does the creek/stream or spring dry out in summer or freeze in winter?
    • Is the ditch water constantly available, does the water in ponds/dams evaporate during the summer heat
    • Is the well deep enough to reliably provide water during the most severe droughts?

    STEP 3. Find out the water source output

    The available volume of water from the water source (the water flow) is measured in gallons/liters per minute.

    • Find out the well or spring flow, have it tested or ask the realtor/property owner.
    • If the land doesn’t have a well, contact local drilling companies so that they give you some data on what might be expected.

    WATER HARVESTING AND STORAGE POTENTIAL

     

    WATER HARVESTING POTENTIAL

    STEP 1. Identify what are the potential surface runoff areas 

    Water can be captured from roof areas, roads, other hard surfaces and the whole site area itself (site’s watershed).

    • Identify the surface runoff areas that would be able to fill potential pods/dams and water tanks.

    STEP 2. Calculate the runoff

    In order to obtain an estimate of how much water you might be getting from the surfaces (A) you identified in step 1, you’ll have to do some calculations.

    • Refer back to the weather data you collected in the locality sheet and find out the average yearly rainfall (R).
    • Multiply the surface area (A) with the average yearly rainfall (R) to gain an estimate of Rainfall volumes (V).

    Rainfall volumes (V) = catchment area (A) x average yearly rainfall (R).

    Example 1: How much water will roof collect?

    To calculate how much water your roof will collect, multiply the average yearly rainfall (R) by the roof area of the house (A), For example, for a roof area of 200m2 and an annual rainfall of 1000mm or 1m, 200m3 or 200000l can be collected.

    Note: similar calculations can be made for the entire catchment of the site. However, you won’t be getting a 100% runoff like in the roof example. Instead, you’ll have to calculate the total average run-off figures.

    (1) Rainfall Volumes (V) = Catchment of the site (A) x Average yearly rainfall (R) (2) Estimate of runoff volume = Rainfall volume (V) x Runoff coefficient (C)

    Example 2: How much water will a pond collect?

    To calculate how much water your pond will collect, multiply the average yearly rainfall (R) by the catchment area of the site (A). Then, multiply that number with a runoff coefficient that reflects the properties of your site. Find more about what runoff coefficient to use here.

    WATER STORAGE POTENTIAL

    PART A: PLOT CONTOURS ONTO GOOGLE EARTH

    STEP 1. Locate the property on the Contour Map Creator website

    • Open the http://contourmapcreator.urgr8.ch/ website and zoom in on the property.

      Note: Don’t zoom in too much as you’re trying to get the overall picture of the topography surrounding the property as well.

    STEP 2. Draw a sampling area

    • Mark a rectangle by adding two pins onto the maps.

    STEP 3. Get a contour map

    • Adjust the plot options, use level interval of 5m/15ft

    • Click ‘Get Data’, use the sampling tab.

    STEP 4. Import contour into Google Earth

    • Scroll down and press ‘Download KML file’.

    • Once the file is downloaded, open it in Google Earth.

    PART A: ASSESS THE TOPOGRAPHY

    STEP 1. Locate the property on Google Earth

    • Launch the Google Earth application and zoom in on the property.

    • Enable the newly imported ‘Contours’ kms file in the sidebar under the places bar.

    STEP 2. Assess the topography for potential ponds/dam sites

    Keypoint/Gully Pond

    • A keypoint can be found on topographical maps where the contour lines of a valley begin to get further apart. (image credit: Georgi Pavlov)

    Saddle Pond

    • Located in the lower ground between two hilltops.

    Hillside/Contour Pond

    • Located on the side of hills. Look at your topographic map and check for any widening of the contours along the hillside.

    Ponds for flat sites

    • All these are suitable for flat sites, and since they cannot capture runoff, they need to be filled from external sources.

    Type #1 Risk Assessment:

    People generally underestimate how much water they consume and how much water they’ll need for their farm. The maths around these numbers can be brutal, for example – a typical North American consumes 75 to 100 gallons or 300 to 400 liters a day per person. That works out at about 366,000 liters (96,686 gallons) a year just for personal water consumption.

    Even a modest garden will require thousands of liters/gallons a week. Irrigating a 1,000-square-foot (~100-square-meter) garden at the recommended rate of one inch per week will use 600 gallons (2730 l) each time. If for example, a garden is 5,000 square feet (465 square meters), that’s 3,000 gallons(13600 l) a week!

    Buying a property where you can’t build a structure to harvest necessary water or buying land without a well offers a serious risk of type #1 error.

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