Run-off water management

“Neot Shoshanim” basin in Holon

 

Final project

Faculty of architecture and town planning in the Technion – landscape architecture

 

 instructors: architect Matanya Sack & landscape architect Sachar Zur

Advisors: landscape architect Barbara aronson

yael dori -Israel Union for Environmental Defense

The project suggests four steps on a strategic level:

 

Identification and mapping of the watershed's boundaries and the capacity of the runoff

The projects maps the boundaries of the 360 dunams watershed. It is apparent that only 19% of the area allows seepage, and there is no direction of runoff to these areas. A simple calculation shows that the whole watershed (only sub-watershed Neot Shoshanim) produces about 5,800 cubic meters of runoff in the frequent occurrence of 20 millimeters rain.

Additional mapping that was done during the work on this project examines the morphologies in the watershed and their level of influence / contribution to the total amount of runoff.

Deconstruction and replacement of hard / paved surfaces

Replacement of land cover according to the mapped areas, replacement of paved "deserts" in the Gan HaZikaron public space specifically, and in parking lots around the watershed in general. The plan that was proposed for just half the area of the watershed (the lower area), increased the seeping surfaces from 19% to 25%, resulting in 864 cubic meters less runoff in a 40 millimeter rain occurrence.

Logical directing of runoff

The open public spaces that are capable and "want" to receive runoff are planned in a way that allows them to produce runoff and direct it to the city drainage system. By simple actions, it is possible to direct runoff to these public spaces and use them to relieve strains and create old-new landscapes that are so typical to the city of Holon. Holon is built upon a bed of sand dunes, a great ground for seepage, being able to seep in large amounts of runoff in a relatively short period of time. It is also capable of filtering road washings and some of the pollutants before they reach groundwater.

Creation of a new low point, lower than the existing one

The most significant step that the plan proposes focuses on two existing open public spaces, Gan Nahman and Gan HaZikaron. The plan proposes to lower these sites beyond the lowest existing point in the watershed, and by doing that to prevent water damage to property. It also aims to connect between runoff and groundwater.

The increase in population brought along a growing demand for water to develop residential, industrial and commercial areas, as well as infrastructure, roads, employment centers, public buildings and others. Meeting the increasing demand gradually puts strain on the water cycle. On one hand, more land is used for development, resulting in less seeping areas. On the other hand, more water is being pumped out in order to meet the increasing demand. 

Every one of us is somewhat responsible for the dwindling and violation of natural areas. We all live in a building that are sealed to water penetration, we all drive fast in our cars on sealed asphalt and we all walk on paved surfaces.

Holon region, which was selected as the study case for this project, is Waterproof in about 78% of its built areas – it has 11,000 dunams of non-seeping land cover out of about 15,000 dunams of built areas. The meaning of these numbers in terms of water is that 5,500,000 cubic meters of runoff in a rainy season that are drained into the drainage system and from there to the ocean. This data is paired with the fact the Holon has a population of 183,300 (CBS, 2013), when the water usage is an average of 165 liters per person per day, which add up to 10,352,830 cubic meters a year.

Holon has approved a plan for building thousands dunams neighborhood of thousands of housing units on its last land reserves. Naturally, this will greatly reduce the seeping areas and will increase the demand for water.

The level of groundwater underneath Holon, that has 21 wells, has decreased from elevation of +6 meters in 1958 to an elevation of -3.5 meters in 1987 (CBS, 2014) – a decrease of 9.5 meters, which caused the closing of 8 wells due to salinization or contamination. However, recent media reports show increasing amount of water damage events like floods and soil weathering.  

Most of Holons watersheds drain to Ayalon stream, as the watersheds of the cities Bat-Yam, Rishon LeZion and large parts of Tel-Aviv. These strain the cities' drainage system while it functional on its maximum capacity. 

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