Tel Aviv has NIS 1b plan to cope with floods

Seven years ago, as part of its master plan for managing water runoff, the Tel Aviv municipality commissioned guidelines for managing water runoff from Studio Urbanof landscape architect Leor Lovinger. The document reviewed the municipal drainage system, identified and listed the bottlenecks in the system, and proposed planning solutions. This author was part of the team writing the report.

Instead of renovating the existing drainage system, which would require difficult engineering work, including digging and blocking off roads, planning, and landscaping ideas were proposed making it possible to halt or delay flowing water and divert it to groundwater levels.

The proposed solutions included preliminary planning taking into account the natural topography and making it possible to turn low places into parks used as focuses of delayed drainage and seepage. The green area, a garden or park, becomes a place for catching, holding, and storing water runoff; seepage sidewalks with Silva Cell beneath them that store the water runoff; trees planted in the sidewalk as natural runoff managers that collect water in their branches and foliage, slow the pace at which the water reaches the ground, and help clean and purify the water on its way underground; and a pit or swale making it possible to reach the seepage layer. The water seepage rate depends on the depth of the pit.

Yesterday's floods show that Israel has no reasonable preparation for extreme rain events. Gilad Safier, a hydrologist and environmental consultant at Aviv Group subsidiary DHVMED Environment Consulting Engineering, says that the problem is nationwide. "The main reason for the increase in flooding in Israel is that our cities have grown. What happens is that every developer making a construction plan or building a building drains the water outside. The drainage systems, especially in the older neighborhoods, were planned according to old standards," he says.

Safier adds that drainage infrastructure is the most expensive municipal infrastructure. "The Tel Aviv municipality's masterplan, designed in 2013, is estimated at NIS 1 billion. The idea was that this amount should be invested in order to achieve the objectives. It's obvious that carrying out the project will take decades."

"Globes": Why are there still floods?

Safier: "The main drainage pipeline from the neighborhood to the Ayalon River passes along Lehi Street. Its diameter is 2.5 meters, and that's still not enough. In addition to the money, it's an enormous project that will overturn the entire street. Furthermore, there's an engineering problem that doesn't involve money. There is other infrastructure in the ground, including electricity, communications, and sewage. You want to leave room for tree roots, and there are developers who want to build parking basements in buildings. There's a limit to how much you can expand."

"Why didn't you make Gan Hatikva into a delayed drainage location?

"This option was considered. In order to withstand a rain event that takes place once every 20 years, you have to build a reservoir there. Such a project costs NIS 20 million by itself. In addition, it is an organizational site for the light rail. Until that is finished, digging the garden is a problem."

Safier explains that yesterday's heavy rain type event happens once in 50 years, and so he is less upset about it. "It's important to understand that even after the masterplan is implemented, yesterday's event is exceptional, and can still cause flooding. You can't design municipal infrastructure that will be adequate for an event that takes place once in 50 years or once on 100 years. That's not reasonable," he says.

Sapir says that there is no magical solution, and that the solutions are only in the long term. "The Planning Administration now published draft instructions for management of municipal water runoff. Nothing like this ever been done before. The main goal is for every new plan to set a target for volume of water runoff that the plan will have to manage in its area. Instead of more runoff water let loose outside, it will have to contain the water runoff in its area. This will be a revolution in runoff water management in Israel."

What will happen in the old neighborhoods where there is no urban renewal?

"It's a matter of decades. The solution there is redesigning the parks."

Is it necessary to change the entire country's drainage for two especially rainy days that happen once every 50 years?

"Yes, but slowly. The cost is enormous, and the consequences are enormous. You can't dig up all of the streets at the same time, can you?"

Published by Globes, Israel business news - en.globes.co.il - on January 5, 2020

Tel Aviv has NIS 1b plan to cope with floods

Tel Aviv's drainage masterplan, drawn up in 2013, would channel more water to parks and underground storage.