Exploration and description

River variables

In view of the result shown earlier that snail incidence is associated with altitude and season it is worth summarising mean values for water flow velocity and pH levels in the same way.

Thus, for water flow velocity we can see that snails were found only in the dry season at the five sites where the velocity was in a range of 0.19 to 0.31 m/s. In Site 5 at the highest altitude, where no snails were found, the velocity in the dry season was 0.48 m/s, which is at the lower end of the range of values shown for the wet season and above the value of 0.4 m/s (the upper limit for presence of snails quoted on the previous page).

A similar trend can be seen for pH. Snails were found only when pH values were 7.1 or above.