The Test rises as a winterbourne near Ashe above Overton at roughly 90 m and drops only that much over 64 km to Southampton Water — an average gradient near 0.14%, about as gentle as an English trout river gets. Upper reaches above Whitchurch are seasonal: the spring line migrates downstream through the summer as the chalk aquifer draws down. From Whitchurch through Longparish, Chilbolton, Stockbridge, Mottisfont, Romsey and Broadlands the river runs as a classic low-gradient pool-riffle and glide sequence on clean, well-sorted flint gravel over Cretaceous chalk, threaded through a network of hand-cut carriers and side channels. Baseflow index at Broadlands is around 0.94, which is why the hydrograph is so flat and the bed so stable: Ranunculus anchors in the same gravel for years, and winter spates rarely shift it. Wading hazards are soft marl pockets and silty slacks at the margins, not anything mobile.

Wading: Soft marl pockets and silty margin slacks