Since all of Richmond occupies islands in a river delta, the city has plenty of rich, alluvial soil for agriculture, and was one of the first areas in British Columbia to be farmed by Europeans in the 19th century. The drawback of Richmond's geographical location was that since all the land averages just one metre above sea level, it was prone to flooding, especially during high tide. As a result, all the major islands are now surrounded by a system of dykes, which, although not as massive as those in the Netherlands or the levees of New Orleans, serve to protect the town from anticipated sources of flooding. There is a possibility that, during an earthquake, the dykes could rupture and the alluvial soil may liquefy, causing extensive damage. Richmond is also at risk of a major flood if the Fraser River has an unusually high spring freshet. Recreational trails run along the tops of many of the dykes, and Richmond also supports about of parkland.