A seep spring is groundwater oozing out over a broad wet area instead of one point, so it cannot be caught in a spring box and needs drains and a collection chamber instead. Measure what it gives by digging a short pilot trench, timing the water that runs from it, and dividing by its length: a pilot trench of 2 m that gives 0.4 L/min means 0.2 L/min per metre, and a supply of 10 L/min would need drains about 50 m long.
Part of Spring Capture
A seep spring, or seepage, is a place where groundwater emerges slowly and diffusely across a hillside or a flat, wetting the ground without forming a stream. It is common where a water-bearing layer is cut over a long line.
Many Small Flows Must Be Gathered Into One
At a gravity spring all the water comes out of one eye and a box catches it. At a seep the same water comes out of a broad area at a rate too small to see at any one place. A box would catch only a corner of it. What works is a collecting line that crosses the seep and drains to one point: drains and chambers, described in Collection Chambers. Seeps are often less reliable in dry seasons and more exposed to surface pollution than a spring from deeper ground.
Measure The Yield With A Pilot Trench
You cannot time a bucket under a wet patch. Dig a short pilot trench across the seep, clean it, and time what runs from it.
Worked example. A pilot trench 2 m long dug across the wet area fills a 20 L bucket in 50 minutes after being cleaned and allowed to run. The flow is 20 ÷ 50 = 0.4 L/min.
- Flow per metre of trench = 0.4 ÷ 2 = 0.2 L/min per metre
- The Spring Capture guide’s supply example, 20 L in 2 minutes, is 10 L/min. A trench length of 10 ÷ 0.2 = 50 m would be needed to gather that much
- A supply of 2 L/min (20 L in 10 minutes) would need 2 ÷ 0.2 = 10 m
The scaling is a simplification. Drains placed close together compete for the same water, so doubling the length gives less than double the flow, and the per-metre figure measured in the wet season is higher than in the dry. Use the dry-season measurement (Seasonal Monitoring) and expect to find that a seep supports a smaller group than a gravity spring would.
What You Need
- A spade and a bucket — for the pilot trench and the timing
- A watch
- A tape or cord — to measure the trench length
- A notebook
Method: Dig, Clear, Time, Scale
Step 1: Mark the seep. Mark the wettest ground and the uphill edge of the wet area.
Step 2: Dig the pilot trench across the slope near the uphill edge, to the depth where the water runs in, no deeper than 1.2 m.
Step 3: Let it clear and run for a while until the water is steady and clear.
Step 4: Time the flow from the trench’s lower end into the bucket (Bucket Timing).
Step 5: Divide by the length of the trench and work out the length needed, with the dry-season caution above.
Step 6: Compare against need and decide whether the seep is worth developing, or whether to look for another source.
Common Mistakes
- Using one wet-season measurement. Seeps fall in summer.
- Taking the whole wet patch as the yield. Only what you can gather counts.
- A trench too deep. It collapses, and it cuts below the water-bearing layer.
- Leaving the trench open. Cover or fill it when you finish; an open trench collects dirt.
Safety
Wet banks collapse
Wet ground is the weakest. Do not enter a trench deeper than 1.2 m unless the sides are sloped or shored, keep spoil at least 0.6 m back from the edge, and do not work alone (Excavation).
What’s Next
- Learn next: Collection Chambers — gathering the seep to one point
- Combine with: French Drain Collection — the drains themselves