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Hydraulic and hydrological invariance for urbanization

Hydraulic and hydrological invariance: a requirement for land protection

Hydraulic and hydrological invariance are two fundamental principles introduced by regional regulations, in line with European Directive 2007/60, to mitigate the impact of urbanization interventions on the territory and ensure the safety of citizens. Hydraulic invariance aims to keep the flow of rainwater unchanged, while hydrological invariance focuses on the volume of runoff. The common goal is to prevent flooding, erosion, and landslides to protect the public and infrastructure. To achieve hydraulic and hydrologic invariance, solutions such as detention ponds, green roofs, permeable pavements, and stormwater capture and reuse systems are used.

What are hydraulic and hydrologic invariance?

Hydraulic invariance is the principle that the maximum stormwater runoff discharged from urbanized areas to downstream natural or engineered receptors should not be greater than that which existed prior to urbanization.

Hydrologic invariance is the principle that not only the flow rates, but also the volume of stormwater runoff should not be greater than that which existed prior to urbanization.

In fact, when a natural area is urbanized and all or part of the land is sealed, the permeable surface area is reduced and, consequently, the amount of water absorbed by the land is reduced, the natural runoff volumes are reduced, and the runoff time, i.e., the time it takes for water to run off to its final destination, is reduced. All of this results in a significant increase in runoff flow rates and can cause the ultimate receptors (streams, creeks, rivers) to overflow because they are no longer able to drain the flow properly.

 

To avoid these phenomena, the legislation requires the pursuit of hydraulic and hydrological invariance of land use transformations, which occur, for example, in the case of:

  • the construction of new buildings and extensions
  • paving of outdoor areas
  • construction of new parking lots and parking areas
  • construction of new squares
  • renovations with demolitions
  • construction, rearrangement, widening, adaptation of road and highway infrastructure

How do you apply hydraulic invariance and hydrological invariance?

To prevent flooding and protect the environment, legislation requires hydraulic and hydrological invariance in land development. This means managing stormwater locally, upstream of final receptors, to reduce runoff, rebalance the hydrologic regime and mitigate hydraulic risk. Separating uncontaminated stormwater from contaminated stormwater also helps reduce water pollution. 

Invariance does not necessarily imply the treatment of water, but rather its volanization, i.e. the control of runoff to avoid overloading the final receptors (sewer, river, stream) and that would compromise the hydraulic regime.

Existing regulations and legislation on hydraulic and hydrological invariance

Community, national and regional legislation implements the principle of hydraulic invariance in order to protect the environment and citizens, issuing directives and standards that require greater attention to soil protection. For example, the storage volumes that must be maintained before and after urbanization are defined - volumes that depend on the watercourse into which the rainwater runoff flows. Some of the most important Italian directives are, for example

  • EC Directive 2007/60 Flood Risk Assessment and Management
  • Lombardy Law RR n.7 of 23/11/2017 and n.8 of 19/4/2019
  • Emilia Romagna Hydraulic Directive PAI-PRRA DGR 211272016 (art.2b,3,4,6,7,8,9,10,11 of the Plan)
  • Veneto DGR 2948 of 6/10/2009 related Annex A
  • Marche L.R.2272011 
  • Friuli DGR no.800/2018

IDRO GROUP solutions

To maintain hydraulic and hydrogeological integrity, IDRO GROUP offers a wide range of dedicated services and systems:

  • Technical consultancy in the hydraulic design phase;
  • Technical advice on the plant to identify the best solution;
  • Supply of systems for the construction of water reservoirs (interconnected prefabricated concrete tanks, impermeable tanks with plastic modules, phytoremediation systems, design of large tanks to be built on site). 
  • Specific flow regulation systems to be installed upstream of the flywheel tanks or at their outlet (floating or automatic gates, vortex flow regulators).
  • Overflow screening systems and flywheel tank cleaning systems (tilting tanks, outlet gates, vacuum systems)
  • Water reuse systems (phytodepuration)
  • Construction of infiltration works or areas (infiltration ditches, infiltration basins, filtering storm drains, etc.) to compensate for the sealing caused by urban interventions;
  • Construction of natural or artificial reservoirs to laminate the flow rate and equipped with systems to control the discharged flow rate.


IDRO's solutions and services are aimed at all those involved in the design and construction of buildings, and in the preparation of urbanization interventions that must therefore follow the principles of hydraulic and hydrological invariance, such as

  • Planners (engineers, architects, surveyors)
  • Construction companies
  • Water management companies
  • Private individuals


If you want to know more, do not hesitate to contact us.

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