Each large square is 0.25square metres. The stream covers 8 large squares so the csa = 0.25 x 8 = 2 square metres. (or do it in square cms)
| Part Three: | ||
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| You could measure the stream discharge (possibly in cubic centimetres per second). First you need the stream cross sectional area (below). Measure stream width with measuring tape. Hold the tape taut across the channel and measure the depth regularly across the width (e.g. every 25cm for a two metre wide stream). Plot the figures on graph paper to reconstruct the channel shape and calculate the cross sectional area. Example below | ||
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Each large square is 0.25square metres. The stream covers 8 large squares so the csa = 0.25 x 8 = 2 square metres. (or do it in square cms) |
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| Then you need the stream velocity. How long does a float (e.g. dog biscuit) take to cover 10 metres stretch?. Repeat three times and average. (you could multiply by 0.85 as the surface water is faster than below. Calculate the velocity in metres / sec (or centimetres per sec) | ||
| The discharge is cross-sectional area X velocity in cumecs (or cubic cms /sec) | ||
| However, you might decide that depth is a 'good enough' indicator of discharge (especially if your steam has a rectangular profile like in a culvert). So you just need to measure the depth in cms each day. Take into account the water splashes up around your ruler and use the same measuring point each day. You need at least 15 daily recordings to match against our precipitation and infiltration data. | ||
| We need these readings for immediately after half term. So make a start. | ||
| What else do you need to know? What difficulties do you have? Think about this and ask questions in class. You may need more guidance online. But think and try and solve problems for yourself. | ||