improving the public realm

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MULLASSERY CANAL FRAMEWORK AND CANAL EDGE MASTERPLAN

Figure 18 - The underutilised spaces near Law College hostel and PWD park (Image Credit: Sponge Collaborative)

Potential open spaces in the Mullassery Canal precinct

In the Mullassery Canal precinct area, there are several publicly and privately owned open spaces which are underutilised, and which have potential to become water retention areas in the case of an extreme flood event. Some of the underutilised spaces are discussed below: 1. Priyadarshini park abutting the mouth of the Mullassery Canal 2. Government Law College grounds 3. The Jewish Cemetery (currently under the control of the Archaeological Survey of India and in a neglected condition) 4. The Maharaja’s College Grounds 5. The PWD Park adjoining the Maharaja’s College Grounds 6. Privately owned vacant plots along the Karikkamuri college grounds 7. The GCDA stadium 8. The wetlands adjoining the KSRTC campus 9. The KSRTC bus terminus

An additional pathway for water, in addition to the widening of the canal and stormwater drains, is therefore necessary for effective flood mitigation. The potential of open spaces and streets to perform flood mitigation functions, as yet unexplored, is the key to the Mullassery Canal Precinct Framework plan.

2.1.3 Sponge Approach for a Resilient Kochi: Investing in a Blue-Green Network to mitigate flooding and improving the public realm

Sponge Approach

Based on the above, we propose an alternative approach to waterlogging, which considers protecting existing open spaces which act as retention areas, particularly wetlands and low lying regions, while redesigning open spaces and streets to effectively hold and delay a greater quantity of water from entering the stormwater network so that the drains are not overwhelmed, and water can be diverted away from non-floodable access points, junctions and arterial roads. This approach can be overlaid on top of the current engineering solutions proposed to make gray infrastructure investments like canal widening and stormwater pipes more resilient to extreme cloudburst and excessive storm events.

There is the added advantage that a focus on appropriate design of open spaces and streets results in multiple co-benefits, such as increasing biodiversity, ensuring the activation of public spaces, converting previously neglected open spaces to parks and playgrounds, with access to public amenities for the larger community, and creating a sense of ownership over the public realm and flood mitigation infrastructure by the public at large. The

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MULLASSERY CANAL FRAMEWORK AND CANAL EDGE MASTERPLAN

strategies and tactics behind such an approach range from the design of street profiles as water-conveying channels in extreme rainfall events, naturalising the edge of the canal to reduce runoff coecient, creating central and localised retention areas or “sponge landscapes” , retrofitting public buildings to have green roofs, and creating temporary/floodable or “sponge” landscapes in existing open spaces.

There is a broad scientific consensus for the government to take action towards risk mitigation and climate change adaptation within the specific context of Kochi. We offer a landscape based strategy called a Sponge Framework to build Kochi’s urban resilience by holistically managing water as a resource and investing in blue-green infrastructure to supplement gray infrastructure.

In the face of existing and emerging environmental challenges, Kochi needs to build upon its culture of innovation to invest in a different paradigm of infrastructure. The dominant paradigm of stormwater management in Indian cities relies exclusively upon a historic network of gray infrastructure such as channels, culverts and canals. Flood mitigation in this paradigm is about flushing water towards this gray infrastructure network as quickly as possible so the rainfall ends up in rivers or backwaters. With designed capacities that are no longer sucient to the new urban condition, this approach can no longer support regular monsoon rain and will inevitably fail during extreme cloudbursts. The Sponge Framework uses a landscape approach to supplement existing gray infrastructure by leveraging existing blue-green systems like wetlands, ponds, parks, and urban forests and constructing hybrid blue-green infrastructure that mimics the hydrological function of natural systems within urban streets and open spaces.

Figure 19: From catchment-oriented gray infrastructure approach to watershed-oriented blue-green infrastructure approach (Image Credit: Sponge Collaborative)

Figure 20 below illustrates the challenge of stormwater management and flood mitigation in Kochi’s current urban context. During an extreme cloudburst event, rainfall quickly becomes runoff upon hitting the built-up areas and directly makes its way towards the stormwater channels or canal. Without any resistance, the neighborhood generates peak runoff with little to no lag time. The gray infrastructure may or may not be designed to handle the peak runoff levels, but with little lag time stormwater channels or canals quickly meet their capacities and begin overflowing. As rain continues to pour, runoff can no longer enter the overwhelmed gray infrastructure network and the neighborhood gets flooded. Often, existing waste or debris washed during the rain clogs the inlets into the gray infrastructure channels. This leads to ponding around inlets and low-lying areas begin to flood. An over-reliance on the canal as the main conveyance to flush water out can also be hindered if a cloudburst event

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MULLASSERY CANAL FRAMEWORK AND CANAL EDGE MASTERPLAN

coincides with high tide. Therefore, a resilient stormwater management strategy needs to provide multiple pathways for rainfall to slowly circulate, linger on, percolate, and finally be released so no single choke point or failure of conveyance contribute to devastating floods.

Figure 20: An illustration of how cloudbursts become runoff that quickly overwhelms the gray stormwater infrastructure in urban neighborhoods (Image Credit: Sponge Collaborative)

Figure 21 below illustrates the performance of the Sponge Framework for stormwater management in a similar cloudburst event. In a Sponge City the neighborhood does not strictly rely on gray stormwater infrastructure to immediately convey rainfall. Rather a network of Sponge Streets and Sponge Open Spaces are built within the urban fabric to intercept, delay, detain, and release stormwater runoff before they end up in the canals or stormwater channels. Sponge Streets are redesigned sections that integrate natural systems like bioswales, rain gardens, and treepits so the cloudbursts do not generate peak runoff as quickly and the water has somewhere to slow down or stay. These constructed systems are designed to replicate the conditions of natural ground cover within constrained urban fabric. Similarly, Sponge Open Spaces introduce grade changes, constructed ponds, wetlands, and retention or infiltration areas that channel or store water for the duration of the storm or beyond. When Sponge Streets and Open Spaces are strategically implemented they can form a resilient network with multiple inlets and pathways. This network reduces the level of peak runoff and greatly increases lag time so by the time rainfall ends up in stormwater channels or canals the same volume of rainfall enters the conveyance channels more slowly. This effectively increases the capacity of the gray stormwater network without physically increasing its capacity through expensive retrofitting of dredging.

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MULLASSERY CANAL FRAMEWORK AND CANAL EDGE MASTERPLAN

Figure 21: An illustration of how cloudbursts are handled by a network of Sponge Streets and Open Spaces so the runoff ends up in gray stormwater infrastructure at reduced volumes over a longer period of time (Image Credit: Sponge Collaborative)

Figure 22 illustrates the functional benefits of the Sponge Framework through a simple diagram. When a typical urban neighborhood generates high volume of runoff that ends up in stormwater channels very quickly during a cloudburst event, there are two options to upgrade the infrastructure. The city can embark on a prohibitively expensive project of increasing the size of the stormwater channels, dredging or deeping canals, and building new channels or culverts because the existing capacity is no longer sucient for increased runoff due to urbanization and climate change. Alternatively, the city can embrace the Sponge Framework where capital allocated for traditional stormwater drainage upgrades or upkeep is channeled towards creating a network of Sponge Streets and Open Spaces. This approach reduces the peak volume runoff and increases the lag time i.e. the amount of time rainfall takes to end up in the stormwater conveyance channels. Thus, a network of blue-green infrastructure effectively increases the capacity of gray infrastructure without any significant or expensive interventions towards stormwater channels or canals. While this approach is less expensive in the long-run, the initial implementation requires strategic planning and changes in municipal financing, construction, and maintenance protocols which requires time, interdisciplinary collaboration, and political will.

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MULLASSERY CANAL FRAMEWORK AND CANAL EDGE MASTERPLAN

Figure 22: Comparing the hydraulic runoff diagram after a storm event within a typical urban neighborhood exclusively using gray infrastructure and a Sponge neighborhood using a blue-green infrastructure as well as gray infrastructure (Image Credit: Sponge Collaborative)

Finally, the benefit of the Sponge Framework approach is not restricted to flood mitigation. While this approach is primarily geared towards flood mitigation, the integration of Sponge Streets and Sponge Open Spaces creates a number of co-benefits that greatly improve the health and well-being of urban residents. Blue-green infrastructure increases green cover, canopy cover, and introduces new habitats or biomes that increase biodiversity. A Sponge City or neighborhood benefits from improved urban ecology, improved air and water quality, improved health outcomes, increased access to open spaces, and increased real-estate or commercial desirability. Through these indirect benefits, investing in the Sponge Framework generates more value than the initial capital. Cities that have followed through on this approach also saw reduced maintenance cost over time as blue-green systems are more resilient and require less upkeep than gray infrastructure.

Figure 23 illustrates a critical question all municipalities facing flood issues should ask themselves. As we prepare for increased flood risk, should cities spend large sums of money towards the upkeep and expansion of historic gray stormwater infrastructure that mostly stay invisible to the taxpayer or should that money be invested in more resilient alternatives that address flooding and also improve the quality of life for all urban residents? When faced with this question, many cities in the world including US, Europe, China, and Singapore are adopting the Sponge Framework. Copenhagen decided to invest in the creation of 300 public parks designed to handle cloudbursts rather than upgrading their gray stormwater infrastructure. In doing so, the city greatly improved quality of life while also reducing their stormwater maintenance costs by 70%.