{"title":"Drainage Calculator","description":"\u003cdiv style=\"max-width: 800px; margin: 0 auto; font-family: 'Univers', sans-serif;\"\u003e\n  \u003cdiv class=\"input-group\" style=\"margin-bottom: 15px;\"\u003e\n    \u003clabel for=\"region\" style=\"display: block; margin-bottom: 5px; font-weight: bold;\"\u003eRegion of New Zealand:\u003c\/label\u003e\n    \u003cselect id=\"region\" style=\"width: 100%; max-width: 300px; padding: 8px; border: 1px solid #ccc; border-radius: 4px;\"\u003e\n      \u003coption value=\"\"\u003e-- Select Region --\u003c\/option\u003e\n      \u003coption value=\"auckland\"\u003eAuckland\u003c\/option\u003e\n      \u003coption value=\"wellington\"\u003eWellington\u003c\/option\u003e\n      \u003coption value=\"christchurch\"\u003eChristchurch\u003c\/option\u003e\n      \u003coption value=\"other\"\u003eOther (General Estimate)\u003c\/option\u003e\n    \u003c\/select\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"input-group\" style=\"margin-bottom: 15px;\"\u003e\n    \u003clabel for=\"substrate\" style=\"display: block; margin-bottom: 5px; font-weight: bold;\"\u003eType of Substrate:\u003c\/label\u003e\n    \u003cselect id=\"substrate\" style=\"width: 100%; max-width: 300px; padding: 8px; border: 1px solid #ccc; border-radius: 4px;\"\u003e\n      \u003coption value=\"\"\u003e-- Select Substrate --\u003c\/option\u003e\n      \u003coption value=\"impervious\"\u003eImpervious (e.g., concrete, asphalt, roof)\u003c\/option\u003e\n      \u003coption value=\"pervious\"\u003ePervious (e.g., grass, soil, gravel)\u003c\/option\u003e\n    \u003c\/select\u003e\n  \u003c\/div\u003e\n\n  \u003cdiv class=\"input-group\" style=\"margin-bottom: 15px;\"\u003e\n    \u003clabel for=\"area\" style=\"display: block; margin-bottom: 5px; font-weight: bold;\"\u003eDrainage Area (in square metres):\u003c\/label\u003e\n    \u003cinput type=\"number\" id=\"area\" min=\"1\" value=\"100\" style=\"width: 100%; max-width: 300px; padding: 8px; border: 1px solid #ccc; border-radius: 4px;\"\u003e\n  \u003c\/div\u003e\n\n  \u003cbutton id=\"calculateButton\" style=\"padding: 10px 15px; background-color: #007bff; color: white; border: none; border-radius: 4px; cursor: pointer;\"\u003eCalculate Recommended Drain\u003c\/button\u003e\n\n  \u003cdiv id=\"result\" style=\"display:none; margin-top: 20px; padding: 15px; border: 1px solid #ddd; border-radius: 4px; background-color: #f9f9f9;\"\u003e\n    \u003ch2\u003eRecommended Channel Drain:\u003c\/h2\u003e\n    \u003cp id=\"recommendation\"\u003e\u003c\/p\u003e\n    \n    \u003cp id=\"disclaimer\" style=\"font-size: 0.9em; line-height: 1.5;\"\u003e\n      \u003cstrong\u003eDisclaimer:\u003c\/strong\u003e This calculator provides an indicative sizing guide only. It uses simplified assumptions based on typical rainfall intensities and runoff coefficients for major New Zealand centres. Actual drainage design must comply with NZ Building Code (E1) and AS\/NZS 3500.3:2021 requirements.\n      \u003cbr\u003e\u003cbr\u003e\n      Design rainfall intensities are generally based on 10-minute duration storms for roof and surface drainage. Typical figures for a 10-year ARI, 10-min duration are:\n      \u003c\/p\u003e\n\u003cul style=\"margin-top: 10px; margin-bottom: 10px; padding-left: 20px;\"\u003e\n        \u003cli\u003eAuckland: ~95–110 mm\/hr\u003c\/li\u003e\n        \u003cli\u003eWellington: ~105–120 mm\/hr\u003c\/li\u003e\n        \u003cli\u003eChristchurch: ~75–85 mm\/hr\u003c\/li\u003e\n      \u003c\/ul\u003e\n      These values are drawn from NIWA’s HIRDS database and reflected in NZBC E1 and AS\/NZS tables. BRANZ guidance suggests ~100 mm\/hr for most regions as a practical design figure, with significantly higher values for alpine\/high-rainfall zones (e.g., Arthur’s Pass, Fiordland). This calculator does not account for alpine or extreme rainfall zones and uses the upper end of typical figures for major centres.\n      \u003cbr\u003e\u003cbr\u003e\n      \u003cstrong\u003eImportant:\u003c\/strong\u003e Rainfall intensity drives peak flow in the Rational Method. Underestimating it can lead to undersized drainage systems. If you are working to NZ compliance or detailed engineering design, you should:\n      \u003cul style=\"margin-top: 10px; margin-bottom: 10px; padding-left: 20px;\"\u003e\n        \u003cli\u003eReference NIWA HIRDS v4 or AS\/NZS 3500.3 Table E.1 for accurate intensities.\u003c\/li\u003e\n        \u003cli\u003eConsider return periods (e.g., 10-year vs 50-year) and storm durations.\u003c\/li\u003e\n        \u003cli\u003eConsult a qualified specifier or civil engineer for site-specific design.\u003c\/li\u003e\n      \u003c\/ul\u003e\n    \n    \u003c\/div\u003e\n\u003c\/div\u003e\n\n\u003cscript\u003e\n  \/\/ Shopify-safe wrapper\n  document.addEventListener('DOMContentLoaded', function() {\n    \n    const calcButton = document.getElementById(\"calculateButton\");\n\n    if (calcButton) {\n      calcButton.addEventListener('click', calculateDrain);\n    }\n\n    function calculateDrain() {\n      const region = document.getElementById(\"region\").value;\n      const substrate = document.getElementById(\"substrate\").value;\n      const area = parseFloat(document.getElementById(\"area\").value);\n\n      if (!region || !substrate || isNaN(area)) {\n        alert(\"Please select a region, substrate type, and enter the drainage area.\");\n        return;\n      }\n\n      let rainfallIntensity;\n      let runoffCoefficient;\n\n      \/\/ 10-year storm values\n      if (region === \"auckland\") {\n        rainfallIntensity = 80;\n      } else if (region === \"wellington\") {\n        rainfallIntensity = 90;\n      } else if (region === \"christchurch\") {\n        rainfallIntensity = 70;\n      } else {\n        rainfallIntensity = 80;\n      }\n\n      if (substrate === \"impervious\") {\n        runoffCoefficient = 0.85;\n      } else {\n        runoffCoefficient = 0.2;\n      }\n\n      const areaHectares = area \/ 10000;\n      const peakFlowRate_mps = (runoffCoefficient * rainfallIntensity * areaHectares) \/ 360;\n      \n      \/\/ Round to 1dp as per your preferences\n      let peakFlowRate_lps = peakFlowRate_mps * 1000;\n      peakFlowRate_lps = Math.round(peakFlowRate_lps * 10) \/ 10;\n\n      let recommendation = \"\";\n\n      \/\/ Recommendation logic\n      if (peakFlowRate_lps \u003c= 9.0) {\n        recommendation = \"Consider **RELN Storm Drain™** (90mm outlet, max flow: 9 L\/s) OR **RELN Storm Drain Pro™ (Series 150)** (using 90mm outlet).\";\n      } else if (peakFlowRate_lps \u003c= 13.0) {\n        recommendation = \"Consider **RELN Storm Drain Pro™ (Series 150)** (max flow: 13 L\/s). **Note:** The 100mm outlet must be used.\";\n      } else if (peakFlowRate_lps \u003c= 28.0) {\n        recommendation = \"Consider **RELN Storm Drain Pro™ (Series 200)** (150mm outlet, max flow: 28 L\/s).\";\n      } else {\n        recommendation = \"Calculated flow exceeds 28 L\/s. A detailed engineering assessment is recommended to specify a suitable high-capacity solution.\";\n      }\n\n      \/\/ Added calculated flow for testing\n      recommendation += ` (Calculated peak flow: ${peakFlowRate_lps} L\/s)`;\n\n      \/\/ Using .innerHTML to render the bold tags\n      document.getElementById(\"recommendation\").innerHTML = recommendation;\n      document.getElementById(\"result\").style.display = \"block\";\n    }\n\n  });\n\u003c\/script\u003e","products":[],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0705\/5451\/7802\/collections\/NeyraPavingInterestingUncommonFactsAboutAsphalt.png?v=1773368025","url":"https:\/\/aqualine.co.nz\/collections\/https-aqualine-co-nz-pages-drainage-calculator.oembed","provider":"Aqualine NZ","version":"1.0","type":"link"}