‘Water as an amenity’ as a strategy for a delta city that suffers from stormwater flooding.

A working landscape for New Orleans

First a hurricane, now oil; contemporary New Orleans is revising its relation with landscape and water, out of necessity and out of ambition. Since Hurricane Katrina devastated the city in 2005, the Dutch Dialogue workshops. initiated by local architect David Waggonner and the Royal Dutch Embassy - have engaged in a knowledge exchange aiming for new harmony in the landscape, equally inspired by Dutch water cities and love for 'the big easy'. Dutch landscape architects explore how a transformation of the New Orleans' storm water system can increase stormwater resiliency and at the same time contribute to the revival of the city.

Introduction

Deltas are highly dynamic landscapes, and subject to constant change. As a result, human intervention and innovation has always been necessary to safely live and work in deltas. New Orleans, located at the mouth of the Mississippi river, is a typical urban delta city. Like many delta cities around the world, historically the city has a two-fold relationship with water as both resource and threat.

The location of an urban region in a delta brings prosperity and economic wealth, but at the same time there are disadvantages and challenges to overcome. Being low-lying areas, deltas are prone to flooding by the rivers that form them, large volumes of rainfall typical of coastal climates, and storm surges from the adjoining seas. The rapid urbanization of the worlds deltas puts natural resources at risk and amplifies possible consequence, both economical and psychological, in case of disaster (McGranahan, et al., 2007). The recent concerns about climate change and socio-economic trends of progressing urbanisation and continuing investment make life in the urban delta even more complex, and a sustainable strategy for dealing with water in urban deltas all the more relevant.  

Today's state of affairs in New Orleans

It has now been well over 4 years since hurricane Katrina struck the South Louisiana coastline near New Orleans, flooding 80% of the city up to 3m (Campanella, 2008), and forcing virtually all citizens to evacuate. Substantial investments in flood mitigation infrastructure since 2005 will ensure a better than ever before safety from hurricane threats by 2011. 15 billion dollar has been invested in a hurricane risk reduction system on the perimeter of the city, built by the U.S. Army Corps of Engineers. Once completed it will provide protection against 1/ 100 year storm events, and is designed to withstand a 1/ 500 year storm event without catastrophic failure (USACE, 2008).   These considerable investments however, do little to improve the day to day quality of the living environment for the residents of New Orleans, which varies greatly related to topography. Behind the dikes a two faced city can now be observed:   The historical parts of the city, located on higher grounds, again do well. Flood elevation levels were low here and population reaches close to pre-Katrina levels. Again the  same lively, festive and easy-going atmosphere is buzzing through the streets. These neighbourhoods provide the lush greenery, rich experiences, colonial architecture and bustling life; all that New Orleans is famous for.   However elsewhere large parts of the city are by all means still severely damaged and lack landscape quality. It is in the low-lying suburbs, the former back swamp of New Orleans, that the city's problems concentrate, the lack of landscape quality is most manifest and interventions are most needed. The Gentilly and Lakeview neighbourhoods are typical examples of such low-lying areas and form the focus area of this study.

Lack of landscape quality

Being landscape architects we have tried to tackle four main problems in these areas, which together determine this landscape quality: subsidence, rainflood events, the permanent consequence of vegetation loss, vacancy, and its resulting changes in atmosphere of the neighborhoods.   Subsidence With an at-the-time world-class drainage system the swamps and marshes at the fringe of the city were drained at the beginning of the 20th century. Since then, fast discharge and deep drainage and only small amounts of open water result in a low groundwater table, dry soils and consequently subsidence of these now urbanised, former 'backswamp' lands. Originally slightly above sea level these lands have fallen up to 3m below sea level, causing them to suffer the worst from Katrina's floodwaters. Subsidence complicates the draining of the city and worsens existing water problems by shifting subsurface drains and canals, loosening joints and causing leaks, breaks, and bottlenecks in the system.

Rainflood events

The city has a sub-tropical climate; the annual precipitation is 1572 mm (1961-1990). Rainfall in New Orleans is extremely intensive; rainfall in excess of 75 mm in 24 hours, or 100 mm in 48 hours is an almost annual event in the city (Stuurman in: Meyer, et al., 2009). The effects of climate change mean that New Orleans has to prepare itself for even more intense rainfall events separated by longer periods of drought.

Already today, the large volumes of rain in short time periods often exceed the capacity of the outdated and broken storm water system in the city, inflicting large amounts of property damage, and sometimes even casualties (NWSFO, 1997). Floodwaters can rise up to 60cm during a 1/ 10 year storm event (BCG Engineering, 2003), for which the storage assignment was calculated in this thesis with GIS-tools to be 1.200.000m3 for the residential areas of Gentilly and Lakeview.

The permanent consequence of vegetation loss

Both the strong winds and the brackish flood waters of Katrina destroyed 70% of the urban canopy, an estimated total amount of 100.000 trees (Ierardi, 2008; HikeforkaTREEna, 2009). This negatively impacts the microclimate resulting in a lack of shade during hot summers. The remaining fragmented green structure and barren and deserted looking suburban landscape offers little to no opportunities for local fauna. Additionally the hurricane decimated the tree stock and nurseries in all of South-Louisiana.

Vacancy, and its resulting changes in atmosphere of the neighbourhoods

Heavy emotions after Katrina and unsupported plans for urban renewal led to a 'laissez-faire' policy following the storm; a strategy focussed on short-term recovery. Today, 20% of the New Orleanians have not returned (Times-Picayune, 2009) and it is questionable whether they ever will, as people have rebuild their lives elsewhere in the U.S., leaving their lots empty, overgrown or in ruins in what were once thriving middle class suburbs. The resulting striking image of a perforated urban tissue with closed schools, unreturned grocery stores, and scattered inhospitable structures has a detrimental effect on aesthetics. Large numbers of inactive plots give parts of the area a feeling of neglect and desertedness. In this condition the poor urban environment not only provides limited possibilities for natural life, but also fails to inspire humans, and does not offer reason to spend time in the public space.

New normal conditions

As vacancy is strongly related to topography it is most significant in the lowest area's which sustained the most damage during the storm. In Lakeview and Gentilly over 30% of the residential plots are currently unoccupied, with some neighborhoods close to a 50% loss of inhabitants. It is important to realise that the situation New Orleans faces today are 'New Normal' conditions, no longer solely related to the recovery from Katrina (GNOCDC, 2009). The stabilising rates of return imply the perforated tissue will not heal on its own accord and needs a structural rethinking. At the same time they also offer opportunities for changes in water management.

Compared with an average store/discharge ratio of 9:1 in the Netherlands the drainage system in New Orleans (with a 1:1 ratio) is highly dependent on discharge. Through pumps with enormous capacities (up to 350m3/s (USACE, 2008)) it is attempted to discharge rainwater as quickly as possible to Lake Pontchartain (located north of the city). The frequent rain flood events prove that this strategy is unsuccessful. As such the technocratic system not only functions inadequately, but is also conceptually outdated, belonging to a paradigm characterized by a fight against the water and nature in general. This in contrast to contemporary thinking which is increasingly common in the Netherlands and abroad, and seeks to work with nature, aiming at mutual benefit and to profit from open water as quality in the city's public space (Commissie waterbeheer 21e eeuw, 2000). Additionally, the network of underground canals mean there is virtually no visible surface water within the city, providing little to no resemblance to the native habitats of a delta city. With few or no links to their natural environment, the citizens of New Orleans become detached and unaware of the landscape they live in.

Future Perspectives

We propose a transformation process aimed at a working landscape with as its backbone a re-envisioned storm water system based on a contemporary three-stage-strategy; the retain/store/discharge principle (Commisie waterbeheer 21e eeuw, 2000). This working landscape performs for humans by ensuring a healthy and pleasant living environment, through inclusion of ecological processes. And this working landscape informs humans by inspiring, revealing and triggering the imagination.   The huge amount of space left vacant after hurricane Katrina is considered both a necessity and a chance to implement extensive water and robust structures of native and storm proof vegetation in the Lakeview and Gentilly neighbourhoods.   The strategy finds its inspiration in the richness of the surrounding original landscapes of the Mississippi delta, which are structured by a topographical gradient. Hardwood forest is found along the higher grounds of (former)riverbanks, followed by brackish bald cypress and tupelo swamp forests with saline marshlands closest to the sea. In the suburban area of Gentilly and Lakeview four landscape zones are revealed that refer to those original landscapes, and are further based on  topography, subsidence rate, and problems with rain flooding. The zones provide basic concepts for interventions on all scale levels, addressing the problems stated above. As such the strategy mitigates rain flood events by reducing peak discharge, offers conditions for native, sustainable vegetation and provides attractive public space.   Each landscape zone has its own strategy regarding hydrology and vegetation. Typical species associated with the ecosystems in each landscape zone form the main character, while accent species bring identity in different neighbourhoods within those zones. Native species ensure storm robustness and additionally provide habitat to local fauna. Temporal functions reserve space awaiting development. Tree nurseries can be one of those functions, fulfilling the need for seedlings to reforest the city on the spot, as well as occupying and bringing meaning to neglected land. In a future stage these functions can give way for water bodies that will act as buffer zones and as a beautiful amenity within the neighbourhoods.

In the lowest area's more space is reserved for open water in large surfaces and branching networks, while at the higher grounds wadi's and a higher building density are the main principles. A vital part of the transformation is a new strategy regarding water management, advocating a connected water system based on store-retain-discharge principles. Dutch standards regarding freeboard and the allowed water fluctuation (dH max) were applied and tested. To counteract hazards regarding health issues and water quality technical design principles are developed, which include the prevention of stagnant water through guaranteed flow and ecological mosquito  management. Through incentive planning, the community can and should be engaged with interventions on plot level (e.g. introduce rain barrels, plant native vegetation in gardens and introduce permeable surface materials with wide seems).   Area's with both the most pressing needs and biggest chances should be the starting points from which the new landscape framework grows. By attracting development in the north, the complete area becomes a vital and well connected part of the city, instead of its peripheral position now. The integral approach towards spatial development ensures that investments work towards more than one end at the same time. A working landscape in this way may turn these low-lying areas into attractive and distinctive suburbs that New Orleans and its inhabitants so rightly deserve.

The position of design

The design forms an important part of this research, for only the creation of a design allows for conclusions whether the introduction of surface water in the perforated urban fabric is both possible and sensible, and thus is a valid concept.   New Orleans' large City Park-covering more acres than New York's Central Park-located in the centre of the study area will function as an anchor point and showcase for the new landscape structure in the neighbourhoods. The park is redesigned as a water machine that can store 852.500m3 of water during rain events, 26% of the storage assignment. The park also clearly demonstrates how an interpretation of the former appearance of the landscape can provide a connection with place and nature, and enrich the character and identity of the city.

Three studies show how this landscape looks in the residential context and answer questions on smaller scale levels regarding the strategic allocation of vacant space-voids, plots and medians varying in size-for the working landscape structure. Starting point of the design should be a pattern analysis of the urban fabric, by which opportunities for water storage and urban design can be discovered. The exact scale of the transformation depends on the results of this analysis as well as the ambition level and priorities of the city. It was found that open surface water can offer multiple living environments related to water, and can contribute significantly to the storage assignment. All together this study shows how canals, grass lined swales, nurseries and retention ponds can be developed in order to not only function well but also look good;truly water as an amenity for the great city of New Orleans.

References:

BCG Engineering & Consultants, inc. (2003) 1/10 year overflow: model results vs. actual field data [Map and tabular data] Commissioned by US army corps of engineers, New Orleans: BCG Engineering & Consultants, inc.   Campanella, R. (2008) Bienville's dilemma: a historical geography of New Orleans. Lafayette: Center for Louisiana studies.  

Commissie waterbeheer 21e eeuw (2000) Waterbeleid voor de 21e eeuw. Den Haag: Kwak & Van Daalen & Ronday.   HikeforkaTREEna (2009) Hike for KaTREEna; Replanting New Orleans 4,980 trees and counting , 21 august 2009.  www.hikeforkatreena.com   Greater New Orleans Community Data Centre (2009) Redevelopment now a major driver in neighborhood population shifts, 27 november 2009. http://www.gnocdc.org/RecoveryByNeighborhood/index.html  

Ierardi, K. (2008) Beyond receding waters: devastated by Hurricanes Katrina and Rita, the Gulf Coast finally grows green again - The Free Library. 22 September 2009 www.thefreelibrary.com/Beyond receding waters: devastated by Hurricanes Katrina and Rita,...-a0187926856

McGranahan, G., Balk, D. & Anderson, B., (2007) The rising tide: assessing the risks of climate change and human settlements in low elevation coastal zones. Environment and Urbanization, 19(17).

Stuurman, R. (2009) Subsurface conditions for the reconstruction of New Orleans. In: Meyer, H., Morris, D. & Waggonner, D. (2009) Dutch dialogues: New Orleans, Netherlands, common challenges in urbanized delta. Amsterdam: SUN.

'Water as an amenity' as a strategy for a delta city that suffers from stormwater flooding. National Weather Service Forecast Office (1997) The Historic Southeast Louisiana and Southern Mississippi Flood of May 8-10, 1995. NOAA Technical Memorandum NWS SR-183. New Orleans: Louisiana.

Times Picayune (2009) Recovery by the Numbers, 22 October 2009. blog.nola.com/news_impact/2009/08/katrina-recovery-year4.pdf

US Army Coprs of Engineers (2008) Greater New Orleans hurricane and storm risk reduction system [map], New Orleans: US Army Corps of Engineers.