The Netherlands - Terp Mounds

Early Dutch Flood Protection

Flood protection in the Netherlands did not begin with dikes, land reclamation, and monumental surge gates. When the ‘low countries’ were first settled in prehistoric times, temporary communities were established on natural beach ridges and dunes, the highest topographic features in the area. The settlements were still at the mercy of nature, and communities retreated or perished when exposed to high storm surges. From around 500 B.C. onward, settlements along the Dutch coast were constructed on terps, or artificial mounds built to above typical high tide and surge levels so that communities would no longer be destroyed by floods. In the Middle Ages, large constructed mounds enabled permanent settlement in the fertile areas near the coast and rivers. During flood periods, villagers along with their livestock would retreat to the central mound with little risk of loss of life or property. Indeed, the floods were beneficial, depositing fine sediment in floodplains that helped improve agriculture. The figures below show two persevered terps in the Friesland province of the Netherlands. The terp mounds were a very resilient system against flood protection. For small village populations, terp-building was a great example of smart building. Important structures, such as dwellings and churches, were sited so that vulnerability to flood hazards was greatly reduced, while agricultural fields that could be flooded without significant damage were allowed to be inundated. With sufficient warning, loss of life and property (including valuable livestock) could be virtually eliminated by taking refuge on the terp, while natural processes that encouraged siltation to counter subsidence were not interrupted.

Terp with Church and Houses in Hegebeintum, the Netherlands.

Credit: Rijksdienst voor het Cultureel Erfgoed [7] [CC BY-SA 4.0 [8]], via Wikimedia Commons

Terp with Church and Tower in Ezinge, the Netherlands.

Credit: Rijksdienst voor het Cultureel Erfgoed [9] [CC BY-SA 4.0 [8]], via Wikimedia Commons

Mekong Delta - Floating Communities

The Mekong Delta in Southern Vietnam is characterized by a vast and fertile flood plain, made possible by the presence of delta distributaries, canal networks, and small villages and houses, an important corridor for biodiversity. The region's tropical climate, with a wet season lasting most of the year, calls for adaptation to the ever-flowing waters of the region. The fertile soils and lack of topographic relief in the lower delta and coastal zone compared to the proximal areas with more relief, produced two distinct types of communities. In the upstream delta regions with more topographic relief, communities are organized into villages with a typical cluster of housing or buildings, while, in the lower delta, communities are not organized into villages. Instead, they are spread throughout the delta, lining the channel banks and waterways that run through the district. This primitive smart building suggests that perhaps the floating or elevated houses are near canals to make more space available for agriculture, but also to provide access to transportation. The canals are the main routes for transport in and out of the district, with boats being the main form of transportation for both people and goods. Secondary transportation routes include elevated narrow roadways that run between rice fields, connected through centralized hubs where pedestrians and bikes can be transported across canals by ferries.

Floating market of Cần Thơ, Vietnam.

Credit: By User: Doron [10] via Wikimedia Commons [11], is licensed under CC BY-SA 3.0 [2]

Vessel passing through a canal in the Mekong Delta near the city of Mỹ Tho.

Credit: Daniell Berthold [12], via Wikimedia Commons [13], is licensed under CC BY-SA 4.0 [8]

Despite the adaptation of communities to living with water in the Mekong delta, climate change-driven sea level rise, drought, and river floods remain a threat. The Vietnam Ministry of Natural Resources and Environment predicted in 2012 that a 1 m increase in sea level would inundate approximately 39% of the lower Mekong delta basin. The risk to these communities might be even higher if one considers droughts and floods inundating agricultural land, damaging crops, and potentially disrupting the food supply. As a result, the Asian Management and Development Institute is working with coastal provinces of the Mekong on community adaptation programs to better understand and prioritize climate risks and take actions to strengthen their resilience to food and livelihood insecurity resulting from climate change. The adaptation is needed to ensure key income continuity, sustenance food sources generated through rice production, aquaculture (shrimp and clam), livestock rearing (ducks and pigs), and coastal shellfish farming.

New Orleans

Early Smart Building along the banks of the Mississippi River

It is a common misconception, widely promulgated during the media’s coverage of Hurricane Katrina, that the city of New Orleans is below sea level. In fact, almost 53% of the city is at or above sea level (Campanella, 2007). Before the construction of flood protection levees along the Mississippi River, seasonal spring floods caused the river to overflow its banks, depositing sediment in the floodplain along both sides of the river. Sediment deposition was most intense directly at the bank and decreased with distance from the river, gradually building up a natural levee elevated above the surrounding land and typical river stages. From the topographic high of the natural levee, the land surface slopes downward to the below sea level backswamp. The natural levee of the Mississippi is visible in the map of above sea level elevations in New Orleans below, following the crescent shape of the river.

Another major above sea level topographic feature in New Orleans is the Metairie/Gentilly Ridge, a single feature that is known by either name depending on which part of the city it traverses. Formed by the natural levees of a relic distributary of the Mississippi River when its mouth was to the east of New Orleans, the ridge sits several feet above sea level and the surrounding lowlands. The Esplanade Ridge, also formed by a small Mississippi River distributary channel, connects the Metairie/Gentilly Ridge to the river’s natural levee. Most other areas in the city above sea level are artificial, the result of land reclamation along the lakefront, dredged material disposal along navigation canals, and construction of flood protection levees.

New Orleans Elevations above 0 m, NAVD88. Note that the highest elevations are along present and former distributary channels within the delta.

Credit: Map courtesy of Kevin C. Hanegan. Elevation Source: Love, M.R., C.J. Amante, L.A Taylor, and B.W. Eakins, 2011 Digital Elevation Models of New Orleans, Louisiana: Procedures, Data Source and Analysis, NOAA Technical Memorandum NESDIS NGDC-49, U.S. Dept. of Commerce, Boulder, CO, 46pp Imagery Source: USGS Imagery Topo from The National Map

New Orleans was established as a French colony on a crescent-shaped piece of land between the Mississippi River and Lake Pontchartrain, about 80 km from the river’s mouth. The original settlement was built on high ground adjacent to the river and was bordered by low-lying cypress swamps to the North. A map of the further-developed city in 1829 is given below, with some constructed drainage canals already visible. Note that the city is confined to areas above sea level, the river’s natural levee and a small settlement on the Gentilly Ridge connected to the French Quarter by the Esplanade Ridge.

New Orleans city plan in 1829.

Credit: Independent Levee Investigation Team, 2006

During the city’s early development, historic homes in the area employed a smart building approach despite being built above sea level. Realizing the threats of flooding from both the river and the sea, early New Orleans residents showcase houses that are elevated with elaborate architecture or houses that employ basements that are actually on the first floor. Some examples of these houses are shown below and show how well-prepared the communities were as a result of living with and being surrounded by water.

Historic houses in New Orleans. Note that despite being built above sea level, most of the houses are elevated above street level by 1 – 3 m.

Credit: Image courtesy of Community Elevation Program, University of New Orleans Center for Hazards Assessment Response and Technology – UNO CHART

New smart building practices in New Orleans. These houses, built in the Lower Ninth Ward, are energy efficient, utilize modern designs, and are elevated much above their predecessor buildings that were destroyed by Hurricane Katrina.

Credit: Image courtesy of Make it Right Foundation

Due to its unique geography, New Orleans is subject to three types of flood risk: river floods from the Mississippi River, storm surge-induced floods from Lake Pontchartrain and Lake Borgne to the East of the city, and heavy rain-induced flooding due to the low-lying city’s poor drainage. The realization of these threats throughout the city’s history has influenced the development of its flood protection system. From its inception, New Orleans was routinely flooded by the high spring runoff floods of the river. To prevent these floods, the same strategy of heightening the natural overflow banks has been implemented at various scales. Though it did not directly inundate New Orleans, the great Mississippi flood of 1927 resulted in the authorization of the Mississippi Rivers and Tributaries Project, whose construction ensured protection from further river floods. Levees were constructed along most of the lower Mississippi River with 7.5 m above sea level levees fronting the city of New Orleans.

The Netherlands

The terp mounds were a very resilient system against flood protection. However, the size of the constructed mounds was limited and they could only support small villages. With continued population growth and the need for more protected space in villages, the Dutch began building ring dikes around towns. As settlements continued to expand into the low, coastal areas, the land was drained using increasingly elaborate means (ditches, windmills, steam pumps). This drainage, coupled with peat harvesting and poldering (a method used to reclaim land from the sea), caused extensive subsidence, which increased flooding vulnerability. The increasing populations and value of property inhabiting lowlands required higher and stronger dikes, so much so that now most of the Dutch population and economic activity is supported by areas below sea level that are protected from floods by massive, nearly indestructible dikes and surge barriers. With such high consequences of flooding, dikes, and barrier structures for much of the country are designed to protect against a flood with a 1 in 10,000-year recurrence interval.

Learning Check Point

Objective: Understand the benefits of building with nature, and distinguish smart building approaches.

Although this Learning Check Point is not for credit, you will be expected to understand this material for the Module 10 Quiz.

Watch the required video Protecting Against Flooding: Holland's storm-surge barrier [6] (9:43) about the “Deltaworks” flood protection system in the Netherlands. Answer the questions below.

Amsterdam

Modern Floating Houses

Driven by a lack of space on land to expand, the proximity of water has driven the concept of a houseboat to extremes in Amsterdam and around the world. Originally docked in canals, houseboats are now taking a new shape. They are redesigned to be just as good, if not better, than their land counterparts, and are taking shape over water. Small communities of floating houses are rapidly evolving, to fill the growing need. Watch the following video to learn more about the new construction of floating houses.

Video: Living on Water: Sustainable Housing in Amsterdam (5:40)

Greater New Orleans

The city of New Orleans' expansion was partially driven by the need for space (to expand) and the unavailability of sufficient space above sea level. Driven partially by flood protection measures due to the Mississippi River and Tributaries Project, the city expanded into the former back-swamp north of its original footprint. Small-scale levees, termed drainage levees, were constructed on the South shore of Lake Pontchartrain and drainage canals were dredged so that floodwaters could be conveyed out to the lake. To facilitate drainage from an area that is shaped like a bowl (recall Digital Elevation map earlier), an elaborate system of pumping stations, in conjunction with the levees, had to be built. Despite these improvements, the city was still frequently flooded by hurricane-induced storm surge, including major floods in 1947 and 1965. These events, and particularly Hurricane Betsy in 1965, resulted in the inception of another federal project, where the Lake Pontchartrain levees were raised to the current elevation. But the lack of space to construct strong earthen levees, such as those that line up the Mississippi River banks, called for a hybrid construction method. This included the addition of sheet pile walls added atop the existing drainage canal levees, forming the foundation for the concrete floodwalls. These structures failed catastrophically during Hurricane Katrina. The figure below gives a typical cross-section of the city, stretching from the river on the left to the lake on the right.

Levees in the greater New Orleans area and failures during Katrina. Learn about the largest pump station in New Orleans. [15]

Credit: Independent Levee Investigation Team, 2006

Was the catastrophic flooding from Hurricane Katrina due to false protection and unknown risk? To partially answer the above question, we examine city urbanization patterns with the city topography and flood depths from the widespread event that provided the only data point for flooding post-1965. Historically, and to accommodate the growing population of the city, settlement expanded from the crescent-shaped high ground that was organized along the natural levees of the Mississippi River into the former backswamp areas. This expansion would not have been possible without the development of cutting-edge pumping technologies coupled with an elaborate and challenging levee building construction. These technologies first enabled the swamps to be drained, promoted development to extend into these low areas, and helped keep the city drained during heavy rainfall. But, the modifications that took place post-1965 were proven to be the most vulnerable and were not really tested until decades later. While still not immune to flooding risks, areas above sea level in the original city plan were significantly less vulnerable and fared relatively well during Katrina. Recall the DEM at the beginning of the module, and now examine the figure below. From the figure to the left, it can be seen that New Orleans did not expand significantly into low-elevation areas until the late 19th century, exposing the population in the newly-settled areas to elevated flood risks. Up until this point, the settlement patterns of the city clearly followed smart building principles, where development was generally limited to the higher elevations of the natural levees and relic distributary ridges. False protection, afforded by the levees and an elaborate pumping system, produced peace of mind but without contingency or layered defense concept/approach, and resulted in catastrophic flooding when the levees failed.

Historic expansion of the Greater New Orleans Area (left panels) compared to flooding depths resulting from levee failure during Hurricane Katrina in 2005 (right panel).

Credit: Left panel from Campanella 2007. Right panel, from the National Oceanic and Atmospheric Administration (NOAA)

Case Study 1: The Thames Barrier

The Thames Barrier spans 520 meters across the River Thames near Woolwich, protecting 125 square kilometers of central London from flooding caused by tidal surges and storms from the North Sea. The barrier became operational in 1982 with 10 steel gates that can be raised into position across the River Thames. When raised, the main gates stand as high as a 5-story building, are as wide as the opening of Tower Bridge, and weigh about 3,300 tons. The barrier is closed under storm surge conditions to protect London from flooding from the sea, but may also be closed during periods of high flow, to reduce the risk of fluvial (river) flooding in some areas of west London including Richmond and Twickenham. The Environment Agency (the agency responsible for the barrier operation) receives information on a potential surge from a variety of sources including weather satellites, oil rigs, weather ships, and coastal stations. At the onset of a predicted surge, the Thames Barrier will close just after low tide, or about 4 hours before the peak of the incoming surge tide reaches the barrier, a process that takes about 1.5 hours for all 10 gates. The Barrier will remain closed until the water level downstream of the Thames Barrier has reduced to the same level as upstream. As of March 2014, the Environment Agency has closed the Thames Barrier 174 times since it became operational in 1982. Of these closures, 87 were to protect against tidal flooding, and 87 were to alleviate river flooding.

Video: How does the Thames barrier protect London from floodings (00:43)

Figure 10.12: The Thames Barrier is one of the largest movable flood barriers in the world. The Environment Agency runs and maintains the Thames Barrier, as well as London’s other flood defenses.

Credit: Environment Agency, UK [17]

Case Study 2: The New Hondsbossche Dunes – Netherlands

The New Hondsbossche Dunes project – one of many examples of the Dutch government’s approach to smart building that utilizes natural processes – initiates and sustains continued dune nourishment. The principle of 'building with nature' is fully exploited to strengthen the Dutch coastline using a plan that couples smart building with layered protection. Superior to fixed solutions or hardscape approaches, the project employs nature to create a place with varied topography, complete with existing dunes overgrown with native vegetation, young drifting dunes and dune valleys, and a beach of varying width, all designed to be consistent with the existing dunes and to minimize dune erosion. The dunes offer natural mitigation from storm surges, with the added benefit of supporting a diverse population of plant and animal species. The plan is considered to be a dynamic solution because shifting sands and vegetation interact with the beach environment and continue to evolve organically and further bolster recreational activities.

Figure 10.13: A layered design showcasing the benefits associated with dune construction along the northern part of the Netherlands.

Credit: The New Hondsbossche Dunes/West 8 [18] via Architizer [19]

Case Study 3: The Sand Engine – Netherlands

Similar to dune restoration or creation, beach nourishment is a common soft approach to offset erosion. Sand can be mechanically pumped to replenish a beach following a storm or as part of a beach or barrier island restoration project. Alternatively, the natural process of longshore drift transports sand along the coast, not only eroding beaches but also accreting sand and building beaches. In either the mechanical or natural case, the addition of sand to the nearshore zone or beach increases local sediment supply. Mechanical spreading of pumped sand along the coast is common but can have a large ecological footprint and can be very expensive because the sand must be dredged, then transported, and finally distributed along the shoreline – sometimes over considerable distances. To minimize ecological damage and reduce cost, the Dutch developed an innovative way to let nature distribute the sediment instead, making the processes originally responsible for erosion now work on helping to accrete the beaches, at least locally. The concept is not new, but this was the first time that a natural nourishment project of this magnitude was carried out.

The evolution of the sand engine from its construction and dredged placement (top panels) to its natural reshaping by tidal currents and waves (low panels).

Credit: Google Earth

Case Study 4: MOSE flood barrier in Venice, Italy

Although the threat is different from that in the case of the Thames Barrier, like London, the gated flood defenses of the MOSE project in Italy are designed to protect Venice from high tides and surges from the Adriatic Sea, thereby reducing flood frequency. The project takes advantage of the three main tidal inlets connecting the Venice lagoon to the sea, where a series of hollow gates on hinges initially resting on the bed will rise and close the inlets during periods of high tides. The MOSE barrier uses a completely different method than the approach used in the Thames Barrier. The idea, however, is similar in that for much of the time, when there is no imminent threat of flooding, the gates are filled with water and resting on the seabed; when floodwaters threaten Venice, the gates are closed in response to incoming high water. The smart building elements in this approach are in the design, the operation, and the utilization of processes and water properties to minimize operating costs, energy, and maintenance. The gates simply close under the influence of gravity by slowly filling up with seawater, and once fully open, the added weight of the steel when added to the weight of water keeps them submerged. To close the gates, the opposite of gravity, buoyancy, is used. Pumped air forces water out of the gates, and since the air density is more than a thousand times less than seawater, the gates are lifted into the closed position, rising above the water surface. The lack of mechanical infrastructure and arms to perform these steps keeps operating cost low, although, as we learned in earlier modules, the upfront capital costs for such projects can be in the billions of dollars.

Case Study 5: Protecting Tidal Flats and Marsh Edges with Artificial Oyster Reefs

“Ecosystem engineers” use ecosystems whose species’ activities are able to modify the local physical environment, for instance promoting sedimentation or assisting in the self-organization of landscapes. Ecosystem engineers have found that salt marshes, mangroves, and other habitats that can be effective agents for enhancing coastal protection.

In one of the most versatile ecosystems used by ecosystem engineers, oysters transform soft sediments into hard to form complex 3D structures (i.e., reefs) that modify the near-bed water flow and dissipate wave energy, thus influencing sediment transport dynamics and promoting sedimentation in nearby environments. Oyster reefs offer additional ecosystem services, such as water filtration, and their aggregations and biogenic structures facilitate dense assemblages of invertebrate species, as well as provide shelter and foraging grounds for juvenile fish and crustaceans. Oyster reefs are among the most diverse marine habitats.

In one instance of ecosystem engineering, oysters are used in clusters within arrangements of rebar to provide the basis of what will eventually become a reef and help reduce wave energy transmission onto the marsh edge and platform. This approach helps reduce the direct breaking wave energy arriving at the marsh edge and ultimately reduces shoreline erosion. Applications using such solutions include navigation channels and natural waterways where commercial and/or recreational traffic produces above-normal wave energy. The area between the reef and the marsh experiences increased sedimentation, which helps deliver more sediment onto the marsh platform; over time, this sediment accretes to a shallow slope that helps dissipate energy further, and potentially offsets erosion.

Another application uses gabions filled with oysters and oyster substrate to protect tidal flats. Tidal flats provide a variety of ecosystem services, but sea level rise and human-induced stresses are causing widespread erosion. To combat this erosion, experiments in the Eastern Scheldt estuary in the Netherlands (which you saw earlier in this module) use oysters to help reduce wave energy during sub-tidal conditions, trap sediment, and reduce erosion of the tidal flats. Reducing erosion sustains the landform, thereby extending the longevity of the flats and their habitat.

(A) constructed artificial oysters reefs to help reduce wave energy at marsh edges and hence reduce erosion of marsh, and help accrete sediment (B) natural oyster reef in Georgia, USA, at low tide/note that the tidal bar sands are submerged during high tide (C) An oyster reef in the Eastern Scheldt estuary will dissipate wave energy and trap sediment on its landward side, halting the erosion of the tidal flats locally.

Credit: (A) Coastal Environments Inc. (B) Ioannis Y. Georgiou, (C) Ecoshape consortium, Delta Programme, the Netherlands

Learning Check Point

Take a few minutes to think about what you just learned.

Objective: Understand the benefits of building with nature, and distinguish smart building approaches.

Look at the image below.

Figure 10.16: Photograph showing the construction of sand groynes.

Credit: Courtesy of publicwiki.deltares.nl

Figure 10.17: Photo showing concrete cylinders placed to provide erosion protection to the shoreline and serve as substrate for oysters.

Credit: Ioannis Gergiou