{"id":1027097,"date":"2026-01-21T11:26:23","date_gmt":"2026-01-21T09:26:23","guid":{"rendered":"https:\/\/www.nidaplast.com\/?p=1027097"},"modified":"2026-08-27T15:06:34","modified_gmt":"2026-08-27T13:06:34","slug":"stormwater-attenuation-tank-sizing","status":"publish","type":"post","link":"https:\/\/www.nidaplast.com\/en\/comment-dimensionner-un-bassin-dorage-guide-du-calcul-par-la-methode-des-pluies\/","title":{"rendered":"How to size a stormwater attenuation tank: a practical rainfall method guide"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"1027097\" class=\"elementor elementor-1027097 elementor-1014922\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-223bcef6 e-flex e-con-boxed e-con e-parent\" data-id=\"223bcef6\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-e08a5d2 elementor-widget elementor-widget-text-editor\" data-id=\"e08a5d2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"438\" data-end=\"945\"><strong data-start=\"438\" data-end=\"635\">Sizing a stormwater attenuation tank means determining the storage volume required when the flow of stormwater entering the system exceeds the rate at which it can be discharged or infiltrated.<\/strong> The calculation is based on the contributing catchment area, runoff characteristics, local rainfall data, the selected design event and the allowable discharge rate. The required storage corresponds to the maximum difference between cumulative inflow and cumulative outflow during the critical rainfall event.<\/p>\n<p data-start=\"947\" data-end=\"989\">The general principle can be expressed as:<\/p>\n<p data-start=\"991\" data-end=\"1054\"><strong data-start=\"991\" data-end=\"1054\">Storage volume = incoming runoff volume \u2013 discharged volume<\/strong><\/p>\n<p data-start=\"1056\" data-end=\"1298\">The calculation method must always be adapted to the project location. Rainfall data, design return periods, climate change allowances and maximum discharge requirements may vary significantly between countries, regions and local authorities.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-6a0de64 e-con-full e-flex e-con e-child\" data-id=\"6a0de64\" data-element_type=\"container\" data-e-type=\"container\" data-settings=\"{&quot;background_background&quot;:&quot;classic&quot;}\">\n\t\t\t\t<div class=\"elementor-element elementor-element-505ac82 elementor-widget elementor-widget-text-editor\" data-id=\"505ac82\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<h3 class=\"PDq2pG_selectionAnchorContainer\" data-start=\"1300\" data-end=\"1361\">Stormwater attenuation tank sizing: 5 key principles<\/h3>\n<p data-start=\"1363\" data-end=\"1462\"><strong data-start=\"1363\" data-end=\"1382\">Catchment area:<\/strong> identify all surfaces that contribute stormwater runoff to the drainage system.<\/p>\n<p data-start=\"1464\" data-end=\"1585\"><strong data-start=\"1464\" data-end=\"1475\">Runoff:<\/strong> assess how roofs, roads, car parks, permeable surfaces and landscaped areas contribute differently to runoff.<\/p>\n<p data-start=\"1587\" data-end=\"1705\"><strong data-start=\"1587\" data-end=\"1607\">Design rainfall:<\/strong> use rainfall data representative of the project location and an appropriate design return period.<\/p>\n<p data-start=\"1707\" data-end=\"1854\"><strong data-start=\"1707\" data-end=\"1731\">Allowable discharge:<\/strong> determine the maximum flow that can leave the attenuation system according to the receiving system and local requirements.<\/p>\n<p data-start=\"1856\" data-end=\"1990\"><strong data-start=\"1856\" data-end=\"1875\">Storage volume:<\/strong> calculate the maximum volume that must be temporarily stored when incoming runoff exceeds the allowable discharge.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5da238b1 elementor-widget elementor-widget-heading\" data-id=\"5da238b1\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">EN 752 and the principles of stormwater drainage design<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5aac7719 elementor-widget elementor-widget-text-editor\" data-id=\"5aac7719\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"2057\" data-end=\"2239\"><strong data-start=\"2057\" data-end=\"2239\">EN 752 provides a common European framework for drain and sewer systems outside buildings and establishes general principles for their planning, design, operation and management.<\/strong><\/p>\n<p data-start=\"2241\" data-end=\"2319\">For a stormwater attenuation project, the main parameters to consider include:<\/p>\n<ul data-start=\"2321\" data-end=\"2614\">\n<li data-start=\"2321\" data-end=\"2355\">the contributing catchment area;<\/li>\n<li data-start=\"2356\" data-end=\"2400\">the type and permeability of the surfaces;<\/li>\n<li data-start=\"2401\" data-end=\"2430\">the runoff characteristics;<\/li>\n<li data-start=\"2431\" data-end=\"2453\">local rainfall data;<\/li>\n<li data-start=\"2454\" data-end=\"2483\">the selected return period;<\/li>\n<li data-start=\"2484\" data-end=\"2515\">the allowable discharge rate;<\/li>\n<li data-start=\"2516\" data-end=\"2571\">the characteristics of the receiving drainage system;<\/li>\n<li data-start=\"2572\" data-end=\"2614\">any applicable climate change allowance.<\/li>\n<\/ul>\n<p>\u00a0<\/p>\n<p data-start=\"2616\" data-end=\"2794\">The storage requirement is determined by comparing the volume of runoff entering the system during a rainfall event with the volume that can be discharged during the same period.<\/p>\n<p data-start=\"2796\" data-end=\"3008\"><strong data-start=\"2796\" data-end=\"2898\">EN 752 provides general design principles, but it does not replace national or local requirements.<\/strong> The design criteria applicable to a project must therefore be checked according to its geographical location.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-de1fe53 elementor-widget elementor-widget-image\" data-id=\"de1fe53\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" width=\"800\" height=\"450\" src=\"https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1-1024x576.png\" class=\"attachment-large size-large wp-image-1027173\" alt=\"\" srcset=\"https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1-1024x576.png 1024w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1-300x169.png 300w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1-768x432.png 768w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1-1536x864.png 1536w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1-600x338.png 600w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/rainfall-method-curve-1.png 1672w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3e03dfe8 elementor-widget elementor-widget-heading\" data-id=\"3e03dfe8\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Step 1 \u2013 Calculate the contributing catchment area<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5f5579f8 elementor-widget elementor-widget-text-editor\" data-id=\"5f5579f8\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"3070\" data-end=\"3200\"><strong data-start=\"3070\" data-end=\"3200\">The catchment area is the total surface from which stormwater runoff is collected and directed towards the attenuation system.<\/strong><\/p>\n<p data-start=\"3202\" data-end=\"3395\">A development rarely consists of a single type of surface. It may include roofs, roads, car parks, paved areas, permeable surfaces and landscaped areas, each contributing differently to runoff.<\/p>\n<p data-start=\"3397\" data-end=\"3480\">To estimate this contribution, a runoff coefficient can be applied to each surface.<\/p>\n<p data-start=\"3482\" data-end=\"3511\">A simplified relationship is:<\/p>\n<p data-start=\"3513\" data-end=\"3527\"><strong data-start=\"3513\" data-end=\"3527\">Ae = A \u00d7 C<\/strong><\/p>\n<p data-start=\"3529\" data-end=\"3535\">where:<\/p>\n<ul data-start=\"3537\" data-end=\"3627\">\n<li data-start=\"3537\" data-end=\"3575\"><strong data-start=\"3539\" data-end=\"3546\">Ae:<\/strong> effective contributing area;<\/li>\n<li data-start=\"3576\" data-end=\"3598\"><strong data-start=\"3578\" data-end=\"3584\">A:<\/strong> surface area;<\/li>\n<li data-start=\"3599\" data-end=\"3627\"><strong data-start=\"3601\" data-end=\"3607\">C:<\/strong> runoff coefficient.<\/li>\n<\/ul>\n<p>\u00a0<\/p>\n<p data-start=\"3629\" data-end=\"3677\">For a site containing several types of surfaces:<\/p>\n<p data-start=\"3679\" data-end=\"3731\"><strong data-start=\"3679\" data-end=\"3731\">Ae total = (A\u2081 \u00d7 C\u2081) + (A\u2082 \u00d7 C\u2082) + \u2026 + (An \u00d7 Cn)<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-053644b elementor-widget elementor-widget-heading\" data-id=\"053644b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">How do different surfaces affect stormwater runoff?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-26581423 elementor-widget elementor-widget-text-editor\" data-id=\"26581423\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"3795\" data-end=\"3895\"><strong data-start=\"3795\" data-end=\"3895\">The runoff coefficient represents the proportion of rainfall that contributes to surface runoff.<\/strong><\/p>\n<p data-start=\"3897\" data-end=\"4011\">Impermeable surfaces generally generate a greater and faster runoff response than permeable or vegetated surfaces.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-e1d470a e-grid e-con-full e-con e-child\" data-id=\"e1d470a\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-527f8ab e-con-full enfant e-flex e-con e-child\" data-id=\"527f8ab\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-c5406e5 elementor-widget elementor-widget-heading\" data-id=\"c5406e5\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Surface<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1036381 elementor-widget elementor-widget-heading\" data-id=\"1036381\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Roof<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-36d9dd6 elementor-widget elementor-widget-heading\" data-id=\"36d9dd6\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Asphalt<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2c6b1ca elementor-widget elementor-widget-heading\" data-id=\"2c6b1ca\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Concrete<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a9689e7 elementor-widget elementor-widget-heading\" data-id=\"a9689e7\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Impermeable car park<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-4cf0e58 elementor-widget elementor-widget-heading\" data-id=\"4cf0e58\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Landscaped area<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-90b067f e-con-full enfant e-flex e-con e-child\" data-id=\"90b067f\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-a0fe187 elementor-widget elementor-widget-heading\" data-id=\"a0fe187\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\"><a href=\"https:\/\/www.nidaplast.com\/marques\/gamme-nidagrass\/\">Typical runoff behaviour<\/a><\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-09738d6 elementor-widget elementor-widget-heading\" data-id=\"09738d6\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Very high<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a61a26f elementor-widget elementor-widget-heading\" data-id=\"a61a26f\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Very high<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2742b6d elementor-widget elementor-widget-heading\" data-id=\"2742b6d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Very high<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d689585 elementor-widget elementor-widget-heading\" data-id=\"d689585\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">High<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-21da48c elementor-widget elementor-widget-heading\" data-id=\"21da48c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Low to moderate<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-45c07d8 elementor-widget elementor-widget-text-editor\" data-id=\"45c07d8\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"4257\" data-end=\"4484\">The coefficients used for an actual project must be selected according to the applicable calculation method and local guidance. Soil characteristics, slope, surface condition, vegetation and saturation can all influence runoff.<\/p>\n<p data-start=\"4486\" data-end=\"4752\">For example, a 10,000 m\u00b2 site does not necessarily have an effective contributing area of 10,000 m\u00b2. If part of the development consists of permeable or landscaped surfaces, its hydraulic response may be significantly different from that of a fully impermeable site.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6ea1a5b elementor-widget elementor-widget-heading\" data-id=\"6ea1a5b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Step 2 \u2013 Determine the allowable discharge rate and time of concentration<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f49a417 elementor-widget elementor-widget-text-editor\" data-id=\"f49a417\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"4837\" data-end=\"5026\"><strong data-start=\"4837\" data-end=\"5026\">The allowable discharge rate is the maximum flow that can leave the attenuation system. The lower the permitted discharge, the greater the temporary storage requirement is likely to be.<\/strong><\/p>\n<p data-start=\"5028\" data-end=\"5123\">It is generally expressed in litres per second (l\/s) or litres per second per hectare (l\/s\/ha).<\/p>\n<p data-start=\"5125\" data-end=\"5173\">The permitted value may be defined according to:<\/p>\n<ul data-start=\"5175\" data-end=\"5391\">\n<li data-start=\"5175\" data-end=\"5225\">the capacity of the downstream drainage network;<\/li>\n<li data-start=\"5226\" data-end=\"5276\">the characteristics of the receiving water body;<\/li>\n<li data-start=\"5277\" data-end=\"5313\">pre-development runoff conditions;<\/li>\n<li data-start=\"5314\" data-end=\"5338\">flood-risk objectives;<\/li>\n<li data-start=\"5339\" data-end=\"5391\">national, regional or local drainage requirements.<\/li>\n<\/ul>\n<p data-start=\"5393\" data-end=\"5452\">The attenuation system then operates as a temporary buffer:<\/p>\n<p data-start=\"5454\" data-end=\"5504\"><strong data-start=\"5454\" data-end=\"5504\">Inflow &gt; allowable discharge \u2192 water is stored<\/strong><\/p>\n<p data-start=\"5506\" data-end=\"5579\"><strong data-start=\"5506\" data-end=\"5579\">Inflow &lt; allowable discharge \u2192 stored water is progressively released<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-023482b elementor-widget elementor-widget-heading\" data-id=\"023482b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What is the time of concentration?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-9c1d198 elementor-widget elementor-widget-text-editor\" data-id=\"9c1d198\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"5626\" data-end=\"5780\"><strong data-start=\"5626\" data-end=\"5780\">The time of concentration is the time required for runoff from the hydraulically most remote point of a catchment to reach the point being considered.<\/strong><\/p>\n<p data-start=\"5782\" data-end=\"5812\">It depends on factors such as:<\/p>\n<ul data-start=\"5814\" data-end=\"5940\">\n<li data-start=\"5814\" data-end=\"5837\">catchment dimensions;<\/li>\n<li data-start=\"5838\" data-end=\"5846\">slope;<\/li>\n<li data-start=\"5847\" data-end=\"5873\">surface characteristics;<\/li>\n<li data-start=\"5874\" data-end=\"5887\">flow paths;<\/li>\n<li data-start=\"5888\" data-end=\"5906\">runoff velocity;<\/li>\n<li data-start=\"5907\" data-end=\"5940\">drainage network configuration.<\/li>\n<\/ul>\n<p>\u00a0<\/p>\n<p data-start=\"5942\" data-end=\"6106\">The time of concentration helps characterise how quickly the catchment responds to rainfall and can influence the rainfall duration used for hydraulic calculations.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5c1d577 elementor-widget elementor-widget-heading\" data-id=\"5c1d577\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Step 3 \u2013 Use local rainfall data and design return periods\n\nStormwater attenuation tanks must be sized using rainfall data representative of the geographical location of the project.<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5731532 elementor-widget elementor-widget-text-editor\" data-id=\"5731532\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"6304\" data-end=\"6504\">Rainfall intensity varies significantly between countries and even between locations within the same country. Using generic rainfall values can therefore result in an incorrectly sized storage system.<\/p>\n<p data-start=\"6506\" data-end=\"6748\">Design rainfall is commonly characterised using relationships between <strong data-start=\"6576\" data-end=\"6651\">rainfall depth or intensity, storm duration and frequency of occurrence<\/strong>, often referred to as Depth-Duration-Frequency (DDF) or Intensity-Duration-Frequency (IDF) data.<\/p>\n<p data-start=\"6750\" data-end=\"6868\">These datasets make it possible to estimate the rainfall associated with different storm durations and return periods.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a1028af elementor-widget elementor-widget-image\" data-id=\"a1028af\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img decoding=\"async\" width=\"800\" height=\"450\" src=\"https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/carte-des-pluies.webp\" class=\"attachment-large size-large wp-image-1015372\" alt=\"carte des pluies\" srcset=\"https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/carte-des-pluies.webp 1024w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/carte-des-pluies-300x169.webp 300w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/carte-des-pluies-768x432.webp 768w, https:\/\/www.nidaplast.com\/wp-content\/uploads\/2026\/01\/carte-des-pluies-600x338.webp 600w\" sizes=\"(max-width: 800px) 100vw, 800px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1924a04 elementor-widget elementor-widget-heading\" data-id=\"1924a04\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">What is a rainfall return period?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-fe8fe93 elementor-widget elementor-widget-text-editor\" data-id=\"fe8fe93\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"6914\" data-end=\"7041\"><strong data-start=\"6914\" data-end=\"7041\">A return period expresses the statistical probability that a rainfall event of a given magnitude will occur or be exceeded.<\/strong><\/p>\n<p data-start=\"7043\" data-end=\"7055\">For example:<\/p>\n<ul data-start=\"7057\" data-end=\"7257\">\n<li data-start=\"7057\" data-end=\"7142\">a <strong data-start=\"7061\" data-end=\"7086\">10-year return period<\/strong> corresponds to an annual exceedance probability of 10%;<\/li>\n<li data-start=\"7143\" data-end=\"7207\">a <strong data-start=\"7147\" data-end=\"7172\">30-year return period<\/strong> corresponds to approximately 3.3%;<\/li>\n<li data-start=\"7208\" data-end=\"7257\">a <strong data-start=\"7212\" data-end=\"7238\">100-year return period<\/strong> corresponds to 1%.<\/li>\n<\/ul>\n<p>\u00a0<\/p>\n<p data-start=\"7259\" data-end=\"7424\">A 100-year rainfall event does <strong data-start=\"7290\" data-end=\"7297\">not<\/strong> mean that such an event occurs only once every 100 years. Two events of this magnitude can occur within a much shorter period.<\/p>\n<p data-start=\"7426\" data-end=\"7562\">The design return period must be selected according to the applicable standards, flood risk, type of development and local requirements.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-938ebda elementor-widget elementor-widget-heading\" data-id=\"938ebda\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Practical example: calculating the required storage volume<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1c8c754 elementor-widget elementor-widget-text-editor\" data-id=\"1c8c754\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p data-start=\"99\" data-end=\"363\">The useful storage volume of a stormwater attenuation tank is determined by identifying, for the selected design rainfall, the maximum difference between the cumulative volume entering the tank and the volume that can be discharged at the allowable discharge rate.<\/p>\n<p data-start=\"365\" data-end=\"442\">Let us take a simplified educational example for a <strong data-start=\"416\" data-end=\"441\">10,000 m\u00b2 development<\/strong>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-3125900 e-grid e-con-full e-con e-child\" data-id=\"3125900\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-1b5e0f6 e-con-full enfant e-flex e-con e-child\" data-id=\"1b5e0f6\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-e9c3733 elementor-widget elementor-widget-heading\" data-id=\"e9c3733\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Data<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-80bbf7c elementor-widget elementor-widget-heading\" data-id=\"80bbf7c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Roofs<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-fb9e268 elementor-widget elementor-widget-heading\" data-id=\"fb9e268\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Impermeable roads and car parks<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a25d409 elementor-widget elementor-widget-heading\" data-id=\"a25d409\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Landscaped areas<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6202001 elementor-widget elementor-widget-heading\" data-id=\"6202001\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Total area<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2ca12a2 elementor-widget elementor-widget-heading\" data-id=\"2ca12a2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Effective contributing area<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-e26bb0a elementor-widget elementor-widget-heading\" data-id=\"e26bb0a\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Rainfall depth<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-cb7a304 elementor-widget elementor-widget-heading\" data-id=\"cb7a304\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Allowable discharge rate<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-4b36503 elementor-widget elementor-widget-heading\" data-id=\"4b36503\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Duration considered<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-b27ad57 e-con-full enfant e-flex e-con e-child\" data-id=\"b27ad57\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-bf1489d elementor-widget elementor-widget-heading\" data-id=\"bf1489d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\"><a href=\"https:\/\/www.nidaplast.com\/marques\/gamme-nidagrass\/\">Hypoth\u00e8se d'exemple<\/a><\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d1ae859 elementor-widget elementor-widget-heading\" data-id=\"d1ae859\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">3 000 sqm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-09c3222 elementor-widget elementor-widget-heading\" data-id=\"09c3222\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">4 000 sqm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-61c9720 elementor-widget elementor-widget-heading\" data-id=\"61c9720\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">3 000 sqm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-8134aaa elementor-widget elementor-widget-heading\" data-id=\"8134aaa\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">10 000 sqm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1c38f01 elementor-widget elementor-widget-heading\" data-id=\"1c38f01\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">7 200 sqm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f692ba4 elementor-widget elementor-widget-heading\" data-id=\"f692ba4\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">40 mm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-b552786 elementor-widget elementor-widget-heading\" data-id=\"b552786\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">10 l\/s<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-9ed380b elementor-widget elementor-widget-heading\" data-id=\"9ed380b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">60 min<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d481bc8 elementor-widget elementor-widget-heading\" data-id=\"d481bc8\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">1.Calculating the rainfall volume over the effective contributing area<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-16b5dc5 elementor-widget elementor-widget-text-editor\" data-id=\"16b5dc5\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"836\" data-end=\"865\">40 mm corresponds to 0.040 m.<\/p>\n<p data-start=\"867\" data-end=\"893\"><strong data-start=\"867\" data-end=\"893\">7,200 \u00d7 0.040 = 288 m\u00b3<\/strong><\/p>\n<p data-start=\"895\" data-end=\"951\">The theoretical incoming volume is therefore <strong data-start=\"940\" data-end=\"950\">288 m\u00b3<\/strong>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6e29f0d elementor-widget elementor-widget-heading\" data-id=\"6e29f0d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">2. Calculating the discharged volume<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-bb516b6 elementor-widget elementor-widget-text-editor\" data-id=\"bb516b6\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"1000\" data-end=\"1066\">For a constant allowable discharge rate of 10 l\/s over 60 minutes:<\/p>\n<p data-start=\"1068\" data-end=\"1106\"><strong data-start=\"1068\" data-end=\"1106\">10 \u00d7 3,600 = 36,000 litres = 36 m\u00b3<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-adf66e5 elementor-widget elementor-widget-heading\" data-id=\"adf66e5\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">3. Simplified calculation of the required storage volume<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ddaad62 elementor-widget elementor-widget-text-editor\" data-id=\"ddaad62\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"1175\" data-end=\"1196\"><strong data-start=\"1175\" data-end=\"1196\">288 \u2013 36 = 252 m\u00b3<\/strong><\/p>\n<p data-start=\"1198\" data-end=\"1294\">Under the assumptions used in this example, the required storage volume is therefore <strong data-start=\"1283\" data-end=\"1293\">252 m\u00b3<\/strong>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-d228c8e e-grid e-con-full e-con e-child\" data-id=\"d228c8e\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t<div class=\"elementor-element elementor-element-c55afbc e-con-full enfant e-flex e-con e-child\" data-id=\"c55afbc\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-256cf32 elementor-widget elementor-widget-heading\" data-id=\"256cf32\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Step<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3ecad28 elementor-widget elementor-widget-heading\" data-id=\"3ecad28\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Effective contributing area<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-890adef elementor-widget elementor-widget-heading\" data-id=\"890adef\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Rainfall<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0fc11c2 elementor-widget elementor-widget-heading\" data-id=\"0fc11c2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Incoming volume<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-09b283b elementor-widget elementor-widget-heading\" data-id=\"09b283b\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Discharged volume<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-d0a4cae elementor-widget elementor-widget-heading\" data-id=\"d0a4cae\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Simplified storage<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-8e9748b e-con-full enfant e-flex e-con e-child\" data-id=\"8e9748b\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-74cde85 elementor-widget elementor-widget-heading\" data-id=\"74cde85\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Calcul<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-92ce8e2 elementor-widget elementor-widget-heading\" data-id=\"92ce8e2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">Assumption<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-dc84ea4 elementor-widget elementor-widget-heading\" data-id=\"dc84ea4\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">40 mm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-62c3318 elementor-widget elementor-widget-heading\" data-id=\"62c3318\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">7 200 \u00d7 0,040<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-a31fc3d elementor-widget elementor-widget-heading\" data-id=\"a31fc3d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">10 l\/s \u00d7 3 600 s<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-77d60de elementor-widget elementor-widget-heading\" data-id=\"77d60de\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">288 \u2013 36<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-4ef18ed e-con-full enfant e-flex e-con e-child\" data-id=\"4ef18ed\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-52ba9ec elementor-widget elementor-widget-heading\" data-id=\"52ba9ec\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">R\u00e9sultat<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-b287e8f elementor-widget elementor-widget-heading\" data-id=\"b287e8f\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">7 200 sqm<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c226f96 elementor-widget elementor-widget-heading\" data-id=\"c226f96\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">0,040 m<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-9abc06d elementor-widget elementor-widget-heading\" data-id=\"9abc06d\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">288 m\u00b3<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ab8cf07 elementor-widget elementor-widget-heading\" data-id=\"ab8cf07\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">36 m\u00b3<\/p>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7b3e745 elementor-widget elementor-widget-heading\" data-id=\"7b3e745\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<p class=\"elementor-heading-title elementor-size-default\">252 m\u00b3<\/p>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f0cd9ed elementor-widget elementor-widget-text-editor\" data-id=\"f0cd9ed\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"isSelectedEnd\"><strong data-start=\"1572\" data-end=\"1588\">Please note:<\/strong> this deliberately simplified calculation does not, on its own, represent the complete application of the rainfall method. In a real design, several rainfall durations are assessed in order to identify the one that produces the maximum storage volume.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-4809e4a elementor-widget elementor-widget-heading\" data-id=\"4809e4a\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Which parameters should be considered when sizing a stormwater attenuation tank?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-f2ef590 elementor-widget elementor-widget-text-editor\" data-id=\"f2ef590\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p class=\"PDq2pG_selectionAnchorContainer\" data-start=\"1931\" data-end=\"2182\">The sizing of a stormwater attenuation tank depends primarily on the effective contributing area, the design rainfall and the allowable discharge rate. <strong data-start=\"2083\" data-end=\"2182\">There is therefore no standard storage volume per hectare that can be applied to every project.<\/strong><\/p>\n<p data-start=\"2184\" data-end=\"2386\">Two developments with the same total area may require very different storage volumes depending on their degree of impermeability, geographical location, selected return period and discharge constraints.<\/p>\n<p data-start=\"2388\" data-end=\"2685\">The hydraulic calculation determines the required useful storage volume. This requirement must then be translated into a physical solution: an above-ground attenuation basin, an underground attenuation tank, an Ultra-Lightweight Cellular Structure (ULCS) or another solution suited to the project.<\/p>\n<p data-start=\"2687\" data-end=\"2800\">To understand the overall purpose of these systems, see our <strong data-start=\"2747\" data-end=\"2799\">complete guide to stormwater attenuation systems<\/strong>.<\/p>\n<p data-start=\"2802\" data-end=\"3024\">Sizing therefore defines the <strong data-start=\"2831\" data-end=\"2901\">hydraulic requirement before the construction solution is selected<\/strong>. For a real project, the assumptions and results must be validated by the competent project engineer or design consultant.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-54d8dbf elementor-widget elementor-widget-text-editor\" data-id=\"54d8dbf\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p><b>Sources and References :\u00a0<\/b><\/p>\n<div class=\"qMYqUG_convSearchResultHighlightRoot\">\n<div class=\"\" data-turn-id-container=\"request-6a881648-d204-83eb-92ad-acf3cb2a72fc-10\" data-is-intersecting=\"true\">\n<section class=\"text-token-text-primary w-full focus:outline-none has-data-writing-block:pointer-events-none [&amp;:has([data-writing-block])&gt;*]:pointer-events-auto R6Vx5W_threadScrollVars scroll-mb-[calc(var(--scroll-root-safe-area-inset-bottom,0px)+var(--thread-response-height))] scroll-mt-[calc(var(--header-height)+min(200px,max(70px,20svh)))]\" dir=\"auto\" data-turn-id=\"request-6a881648-d204-83eb-92ad-acf3cb2a72fc-10\" data-turn-id-container=\"request-6a881648-d204-83eb-92ad-acf3cb2a72fc-10\" data-testid=\"conversation-turn-32\" data-turn=\"assistant\">\n<div class=\"text-base my-auto mx-auto pb-8 [--thread-content-margin:var(--thread-content-margin-xs,calc(var(--spacing)*4))] @w-sm\/main:[--thread-content-margin:var(--thread-content-margin-sm,calc(var(--spacing)*6))] @w-lg\/main:[--thread-content-margin:var(--thread-content-margin-lg,calc(var(--spacing)*16))] px-(--thread-content-margin)\">\n<div class=\"[--thread-content-max-width:40rem] @w-lg\/main:[--thread-content-max-width:48rem] mx-auto max-w-(--thread-content-max-width) flex-1 group\/turn-messages focus-visible:outline-hidden relative flex w-full min-w-0 flex-col agent-turn\" data-conversation-screenshot-content=\"\">\n<div class=\"flex max-w-full flex-col gap-4 grow\">\n<div class=\"min-h-8 text-message relative flex w-full flex-col items-end gap-2 text-start break-words whitespace-normal outline-none keyboard-focused:focus-ring [.text-message+&amp;]:mt-1\" dir=\"auto\" tabindex=\"0\" data-message-author-role=\"assistant\" data-message-id=\"5d1d09df-9a6e-4340-83fb-76cfb33a1573\" data-turn-start-message=\"true\" data-message-model-slug=\"gpt-5-6\">\n<div class=\"flex w-full flex-col gap-1 empty:hidden\">\n<div class=\"markdown prose dark:prose-invert wrap-break-word w-full light markdown-new-styling\">\n<ul data-start=\"3058\" data-end=\"3928\">\n<li data-start=\"3058\" data-end=\"3300\"><a href=\"https:\/\/standards.cencenelec.eu\/\" target=\"_blank\" rel=\"noopener\"><strong data-start=\"3060\" data-end=\"3146\">CEN \u2013 EN 752: Drain and sewer systems outside buildings \u2013 Sewer system management.<\/strong><\/a> Reference framework covering the planning, design, installation, operation and maintenance of drain and sewer systems.<\/li>\n<li data-start=\"3058\" data-end=\"3300\"><a href=\"https:\/\/community.wmo.int\/site\/knowledge-hub\/programmes-and-initiatives\/water-resources-assessment\/hydrology-publications\" target=\"_blank\" rel=\"noopener\"><strong data-start=\"286\" data-end=\"432\">World Meteorological Organization (WMO) \u2013 Guide to Hydrological Practices, Volume I: Hydrology \u2013 From Measurement to Hydrological Information.<\/strong> <\/a>International reference covering hydrological measurements, rainfall data and hydrological analysis methods.<br data-start=\"541\" data-end=\"544\" \/><br data-start=\"3507\" data-end=\"3510\" \/><a href=\"https:\/\/wmo.int\/publication-series\/manual-estimation-of-probable-maximum-precipitation-pmp\" target=\"_blank\" rel=\"noopener\"><strong data-start=\"3632\" data-end=\"3733\">World Meteorological Organization (WMO) \u2013 Manual on Estimation of Probable Maximum Precipitation.<\/strong><\/a> Technical reference relating to rainfall analysis and the estimation of extreme precipitation events.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n<\/div>\n<\/div>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-7e7499c elementor-widget-divider--view-line elementor-widget elementor-widget-divider\" data-id=\"7e7499c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"divider.default\">\n\t\t\t\t\t\t\t<div class=\"elementor-divider\">\n\t\t\t<span class=\"elementor-divider-separator\">\n\t\t\t\t\t\t<\/span>\n\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-4774d97 e-flex e-con-boxed e-con e-parent\" data-id=\"4774d97\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-469e12a elementor-widget elementor-widget-text-editor\" data-id=\"469e12a\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t\t\t\t\t\t<p><strong>Would you like support with sizing your project?<\/strong><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-40b990a e-grid e-con-full e-con e-child\" data-id=\"40b990a\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t<div class=\"elementor-element elementor-element-0a9e36e elementor-align-center elementor-widget elementor-widget-button\" data-id=\"0a9e36e\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-sm\" href=\"https:\/\/www.nidaplast.com\/en\/contact\/\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t\t\t\t<span class=\"elementor-button-text\">Request a technical study<\/span>\n\t\t\t\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5dc54ba elementor-align-center elementor-widget elementor-widget-button\" data-id=\"5dc54ba\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t\t\t\t\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-sm\" href=\"https:\/\/hubs.ly\/Q04pChRw0\" target=\"_blank\" rel=\"noopener\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t\t\t\t<span class=\"elementor-button-text\">Download the Nidaplast catalogue<\/span>\n\t\t\t\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Sizing a stormwater attenuation tank means determining the storage volume required when the flow of stormwater entering the system exceeds the rate at which it can be discharged or infiltrated. The calculation is based on the contributing catchment area, runoff characteristics, local rainfall data, the selected design event and the allowable discharge rate. The required [&hellip;]<\/p>\n","protected":false},"author":6,"featured_media":1015291,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[391],"tags":[],"univers":[],"class_list":["post-1027097","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-environment-and-sustainable-development"],"acf":[],"permalink_manager":null,"_links":{"self":[{"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/posts\/1027097","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/comments?post=1027097"}],"version-history":[{"count":26,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/posts\/1027097\/revisions"}],"predecessor-version":[{"id":1027725,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/posts\/1027097\/revisions\/1027725"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/media\/1015291"}],"wp:attachment":[{"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/media?parent=1027097"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/categories?post=1027097"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/tags?post=1027097"},{"taxonomy":"univers","embeddable":true,"href":"https:\/\/www.nidaplast.com\/en\/wp-json\/wp\/v2\/univers?post=1027097"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}