Building capacity:// the re-assignment of waterway edge conditions of Sao Paulo’s Favelas
Simon Bussiere 4.5.08
Harvard GSD 6445
Green Infrastructure in the Non-formal City; “Investigation” Report:
Q: How can the Favelas best harness (on-site) storm-water runoff in order to produce the greatest residual social/economic/ecologic net benefit?
Premise:
In the second phase of this research seminar (Green Infrastructure in the Non-formal City: GSD 6445) entitled “Familiarization”, I navigated through and critically analyzed several photographs that Professor Christian Werthmann had taken on his explorations of the Favelas in Sao Paulo, Brazil. Through this macro imaging assessment and a subsequent immersion in contemporary case studies/best practices including the work of Atelier Dreiseitl, Stephen Farber, the Orangi Pilot Project, Wastewater fed Aquaculture in Calcutta and others I am investigating how to best identify opportunities and propose alternative design criteria for the fragile edge conditions of both “unimproved” or disturbed existing streams and highly engineered “solutions/improvements”. Through this exercise it is my goal to better understand “the emerging opportunities of modern sustainable infrastructure for the design of public space” as the datum/direction of this assignment permits.
I’ve drawn from Professor Werthmann’s photographs at five key points along an urban drainage corridor in Sao Paulo’s Favelas to determine a general ratio of impervious to permeable surfaces. The piece of work enabled me to familiarize myself with existing slopes and their contingent visual and topographic impact. In cross-section, the stream corridor reveals a wide set of variables that could be positively manipulated from the tightest alleyways within the highest density settlement patterns all the way to the horizontally sprawling trapezoidal-engineered concrete river beds at the lowest points of the watershed.
Beginning with the premise that conventional engineering principles (under the umbrella of ” storm-water conveyance”) tend to impose a set of abstract assumptions about the quantitative characteristics of water, (deploying a language comprised of terms like sheet flow, peak flow, intensity, duration, discharge, metrics of capacity, etc…) to “capture” and “channel” storm-water as though it were a waste substance that simply needs to be repelled as quickly as is technically feasible “away” from a particular site.
Yet, as the philosopher Foucault reminds us, “Techniques are social before they are technical”…
I would echo this sentiment by asserting that low-tech, low-impact, tactical strategies/interventions utilizing clear and bold gestures of landform and vegetation enable the production of more suitable, empathic, site-specific and cost-effective drainage methods (“solutions”) while empowering/radicalizing on a local level the small-scale community agencies who ultimately contribute, risk, sacrifice and stand to loose or gain the most from the intervening developments within their own sphere of daily activity.
Analysis:
Given the proper term of residency in a given storage/reservoir system, storm-water runoff can be filtered and brought to a point of purification that it would not otherwise achieve within a similar condition/context under the “control” of man-made engineering principles and implemented techniques (as is evident from existing interventions). By this I imply that the conventional engineering of drainage does more to increase the contamination of rainfall once it becomes threaded into a matrix of pipes, catch basins and more pipes. Additionally, the same volume of water when squeezed into a calculated network of impervious trenches drastically increases the velocity at which the runoff travels, thus amplifying downstream erosion and deposition as fluid pressure is abruptly released in a sequence of awkward intervals.
The Bernoulli Principle (thumb on the hose effect essentially), “which states that for an inviscid flow,(like a drainage waterway in the Favelas) an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s gravitational potential energy. (Bernoulli’s principle is equivalent to the principle of conservation of energy). This states that the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remains constant. If the fluid is flowing out of a reservoir the sum of all forms of energy is the same on all streamlines because in a reservoir the energy per unit mass (the sum of pressure and gravitational potential) is the same everywhere”. (Wiki, Batchelor et. al.)
“Fluid particles are subject only to pressure and their own weight. If a fluid is flowing horizontally and along a section of a streamline, where the speed increases it can only be because the fluid on that section has moved from a region of higher pressure to a region of lower pressure; and if its speed decreases, it can only be because it has moved from a region of lower pressure to a region of higher pressure. Consequently, within a fluid flowing horizontally, the highest speed occurs where the pressure is lowest, and the lowest speed occurs where the pressure is highest.” (Wiki)
Bernoulli’s equation[3] is:
(actually, go to wiki… jpegs aren’t inserting here for some reason.)
where:
v, is the fluid velocity at a point on a streamline
g, is the acceleration due to gravity
h, is the height of the point above a reference plane
P, is the pressure at the point
p, is the density of the fluid at all points in the fluid
“The following assumptions must be met for the equation to apply: The fluid must be incompressible – even though pressure varies, the density must remain constant. The streamline must not enter the boundary layer. (Bernoulli’s equation is not applicable where there are viscous forces, such as in the boundary layer).” (Wiki, Batchelor et. al.) The formula/theory has serious implications for how a drainage channel is designed, and it is a tragedy that the integrity of the principles are not more widely accommodated by the engineering community.
“The above equations suggest there is a velocity at which pressure is zero and at higher velocities the pressure is negative. Liquids (and gasses) are not capable of negative absolute pressure, or even zero pressure, so clearly Bernoulli’s equation ceases to be valid before zero pressure is reached. The above equations use a linear relationship between velocity squared and pressure. At higher velocities in liquids, non-linear processes such as (viscous) turbulent flow and cavitation occur”. (Wiki, Batchelor et. al.)
By re-conceiving the “capture” and “channeling” of rainfall and runoff with the basic principles in the above formulas in mind, the negative processes of erosion and deposition can be mitigated, harnessed and potentially exploited to produce substantial social benefits in the form of a usable resource. In the cross-sectional illustrations in this document I have submitted five “sketch” applications according to these principles.
Proposal Summary:
Basic landform manipulation in terms of grading with berms and swales to harness flowing water, when combined with the thoughtful installation of micro- climate sensitive vegetation with slope-stabilizing root structures, porous reservoirs/dry-wells and concrete stabilized block (CSB) pervious paving technologies can greatly mitigate the naturally erosive ramifications of channeled water ways. The edge condition of such riparian corridors represents the terrestrial/surficial opportunity to intervene with such low-tech materiality and high-concept technique. Some of these are explored in the enclosed cross-sections. See attached.
Eventual program(s) that could manifest from this seminar’s research would be in essence, “Ecosystem Services” driven entities/agencies, capable of generating employment and social accountability through the programmatic filter of active storm-water design/construction/monitoring/management. With net water quality gain as the gauge of the long-term success/sustainability of the initiative, the agencies would function as an Infrastructural Urbanist/Acupuncturist who targets “at-risk”/topographically challenging points/neighborhoods/areas along existing waterways and constructs physical systems with improved means of infiltration, storage and treatment through biotope cleansing, (vegetation) berms, swales (landform) stone/adoquine/honeycomb retention reservoirs, and other techniques for mitigating the release of contaminated discharge while accommodating greater carrying capacities in drainage corridors and contingent water sheds.
Obviously, a comprehensive study (on the ground) is needed to identify exactly what methods and “solutions” are appropriate for specific projects, and within particular contexts, including understanding basic user requirements, local skills and skill levels, local wages and labor structure(s), as well as the larger processes and relationships between the individual, the community, the municipality, existing landscape/architectural features, and the greater civic and cultural obligations to the region as a whole.
Like the Social Forestry Program(s) of the Orangi Project in Karachi, the initial intervention of this proposal could incorporate a “Conservation Trust” to oversee and facilitate operations of a set of grading and wetland vegetation planting schema. The Trust could “hire” itself (employing the local labor force) to work with particular sites, amending areas under poor drainage/erosion circumstances with low-tech means that could be built up over time. (note: the Orangi project began with the “National Rural Support Program”/”Rural Pilot Project”, but an urban context could be similarly modeled. I use the term “Trust” to describe a financial institution which would be responsible for spreading the risk of micro-enterprise credits/loans through individuals and social groups interested in investing in local micro-business.
One such business could be involved in the manufacturing of Concrete Stabilized Blocks (CSB’s) comprised of 9 parts earth, 1 part cement and ½ part polyethylene for flexibility. These blocks/adoquines would be the basic building block of the rainwater reservoirs/dry-wells and would also serve as paving units for certain surface treatments. The reservoirs (as illustrated with complimentary plantings) would provide slope stabilization and simultaneously the scaffolding for the re-assignment of specific edge conditions.
Providing storage or containment of runoff for the purposes of filtration and recharge/reuse and purification into potable water is crucial to the success of the ideas proposed here, but it is also important to note that these CSB’s are only one “seed” project to be considered. Other socially conscious employment generating micro-enterprises are capable of transforming the potential of entrepreneurial/opportunistic individuals and communities in the Favelas.
Within the spectrum of “WATER” services would be micro agencies to monitor water quality at specific points along a stream corridor, and other biological treatment stations which would provide training and further educational/technical opportunities. Implicit in the efforts to reconstruct edge conditions of water channels is the presumption that people have the desire to be laborers. But there are great ambitions among the myriad inhabitants of the Favelas and start-up enterprises related to the improvement of water quality could in turn inspire a generation of Biologists, Ecologists and other creative individuals to raise up their neighborhoods to a higher environmental standard and thus promote and produce a greater quality of life.
Sources :
1.Poverty Assessment Report No. 20488-NI, World Bank, 2001
2.Document of The World Bank / Report No.: 39868 / (CREDIT 3085-NI)
June 4, 2007: Project Performance Assessment Report, Second Road Rehabilitation and Maintenance Project, Nicaragua
3.http://en.wikipedia.org/wiki/Bernoulli’s_equation#Incompressible_flow_equation
4.Batchelor, G.K. (1967). An Introduction to Fluid Dynamics. Cambridge University Press. ISBN 0521663962.
5.http://mysite.du.edu/~jcalvert/tech/fluids/bernoul.htm
6.Orangi Pilot Project report on institutions and programs opprti@cyber.net.pk 2007
7.Wastewater Fed Aquaculture in the Wetlands of Calcutta – and overview
Dhrubajyoti Ghosh / Institute of Wetland Management and Ecological Design 1999
8.The Economics of Biodiversity in Urbanizing Ecosystems
Stephen Farber, Columbia University Press, New York 2005
9.Alternative Urban Futures – Planning for sustainable development in cities throughout the world, Raquel Pinderhughes, Rowman & Littlefield Publishers, Inc. 2004
10.Maintaining Connectivity in Urbanizing Landscapes
Sanjayan, M.A. & Crooks, Kevin R. Columbia University Press, 2005
11.Urban Sustainability in the Context of Global Change
Singh, R.B., Science Publishers, Inc. 2001
12.Greening the Built Environment, Smith, Whitelegg & Williams Earthscan Publications Ltd., London 1998
13.Connectivity is a vital element of landscape structure
Taylor, P.D., Fahrig, L., Henein, K., & Merriam, G. Oikos, 1993 68: 571-573.
