I also saw the broadcast. I believe that she mentioned that in the past, sheep and cows used to graze in the hills, and the rain water used to run on the surface. She noted that since the sheep and cows no longer grazed, that the grass became tall, and rain water penetrated the soil and it became unstable. The story is also carried in the Nation Newspaper

Her analysis of the situation is reasonable and insightful. The clay in the Scotland District is almost impervious to water when it is compacted. The hoofs of the grazing sheep and cows can apply sufficient pressure to the soil to compact the surface layers of clay, resulting in water not penetrating into the soil, and instead flowing on the surface.

When clay becomes saturated, and if it is on a hill, then it can slide or slip. If the livestock are no longer grazing, and the grass is allowed to grow, then the roots can penetrate the soil allowing it to become looser over time. Rain water can penetrate loose soil much easier than it can penetrate compacted soil. Loose saturated clay on a slope is vulnerable to land slippage.

The 74 year old Eudora Boyce appears to have carefully observed the evidence, logically analysed it, and provided a reasonable conclusion. Our elderly are truly a treasure of knowledge, and I support our Prime Minister’s call that they should be consulted on drainage matters. Actually, Engineering drainage design manuals normally specify that older persons in the community should be consulted when designing drainage systems.

Thank you for linking.