Building with Nature

Building with Nature: Mitigating Risks While Preserving Natural Processes

The simple concept of sediment supply along the coast and the unified concept of the coastal cell can be applied to other systems. For example, similar to the way a groin disrupts sediment transport downdrift of the structure, resulting in downdrift erosion until sufficient bypassing takes place, land reclamation practices and the construction of levees, seawalls, and other storm protection structures including gates have their effects. On the one hand, land reclamation in tidal systems can alter the tidal exchange of water between the interior basin and the coastal ocean, and may yield sedimentation issues within the basin and near the tidal inlets. On the other hand, erosion within the basin, such as wetland loss, may have the opposite effect, resulting in widespread erosion at the inlets and sediment export due to the increase in tidal exchange. Levees that enclose open or semi-enclosed basins disrupt water, sediment and nutrient exchange and may adversely affect submerged and intertidal habitat, including fish and other aquatic organisms.

Climate change sea level rise will continue to erode coastlines throughout the world for decades to come, and during these transgressive times, we cannot afford to be working against nature. This means that we must first understand the underlying processes governing the transport in the system experiencing these erosional cycles, determine accretion cycles if any, and establish the best approach. Hardening the shorelines by seawalls and levees often implies a permanent boundary. Recall that sea levels rise and fall over geologic time with coastal imprints that spans over generations; therefore if we do not deal with issues now, the next generation will have to. Best approaches, for the most part, imply that we turn to soft, process-driven nourishment of eroding coasts that utilizes natural processes – as opposed to mechanical placement – for the distribution of materials. Often these soft methods are the least disruptive to nature including local and proximal ecosystems.

But we cannot protect cities by nourishment methods alone, and in many cases the installation of levees and other flood control structures will be necessary, especially if cities are already established. Relocation of cities or portions of cities will have catastrophic economic influence. When flood gates are needed, modern designs that utilize natural processes will be favored. An example we saw in the video from the Netherlands is the installation of gates that remain open most times to allow for tidal exchange and facilitate small changes in tidal range to maintain ecosystem function, closing only when cities are threatened by storms. Coupled with layered defenses, a concept introduced in module 8, smart building in many cases can afford the needed protection while helping to lower future energy demands and maintenance costs and achieving overall higher ecosystem services and functions.

The following five case studies will help you learn about how some communities have built with nature to mitigate risks while preserving their natural resources.

• Case Study 1: The Thames Barrier
• Case Study 2: The New Hondsbossche Dunes – Netherlands
• Case Study 3: The Sand Engine – Netherlands
• Case Study 4: MOSE flood barrier in Venice, Italy
• Case Study 5 Protecting tidal flats and marsh edges with artificial oyster reefs