January 28, 2003
The above photo shows the Pennard Pill, a small stream at the Gower Peninsula in south Wales, just before it enters the Bristol Channel. The Bristol Channel has the second highest tidal range in the world (38 feet or 12 m). As shown in the photo, Pennard Pill flows through a steep valley and then meanders toward the Bristol Channel. At times, this stream appears to flow backwards. This results from two factors; the sandy beach in the background, and the huge tidal range.
The beach acts as a retaining wall, built by ordinary tides. These daily tides only affect the stream near its entrance to the channel. However, when a spring tide occurs (high tide occurring one and a half days after the new and full Moon), it can flood the entire valley, and the riverbed is flattened by accumulating sand. The looping meanders here give an indication how slow the river is flowing across the nearly completely flat terrain.