قنات یا کاریز یا کهریز راهآب یا کانالی است که در زیرِ زمین کنده شده، تا آب در آن برای رسیدن به سطح زمین جریان یابد. این جوی یا کانال در عمق زمین برای ارتباط دادنِ رشتهچاههایی است که از مادر چاه سرچشمه میگیرد. مادرچاهها معمولاً یک چشمهٔ زیرزمینی هستند. قناتها بهمنظور هدایت آب و مدیریّت آن برای کشاورزی و سایر مصارف به کار گرفته میشوند. این کانالِ قنات ممکن است تا رسیدن به سطح زمین چندین کیلومتر طول داشته باشد و به محل خروجیِ آب دهانهٔ کاریز و یا سر قنات میگویند.
کاریز واژهای فارسی است و در اصل کهریز و شاید کهنریز و یا کالریز بودهاست. واژهٔ قنات کلمهٔ پارسی معرب شدهاست. در ایران خاوری و افغانستان و آسیای میانه واژهٔ کاریز بیشتر کاربرد دارد و در ایران باختری واژهٔ قنات. قنات خود عربی شدهٔ کنات فارسی است که از ریشهٔ فعل کندن و یا کانال گرفته شده است. جمع قنات را «قَنَوات» گویند.
فناوری ساخت قنات در اوایل هزاره اول قبل از میلاد در مناطق خشک کوهستانی ایران گسترش پیدا کرد و به کشاورزان این مناطق اجازه داد تا بتوانند در دورههای طولانی خشکی که آب سطحی پیدا نمیشود به کشاورزی بپردازند. این قناتها به تدریج در مناطق دیگر دنیا رایج شدند و اکنون قناتهای زیادی از چین تا مراکش و حتی در قاره آمریکا وجود دارند.
ایرانیان باستان در چندین هزار سال قبل دست به این ابتکار جدید زده و آن را کاریز یا کهریز نام نهادند. نخستین قناتها و طولانیترین قنات دنیا در ایران واقع شدهاست. با این اختراع که در نوع خود در جهان بینظیر بودهاست، میتوان مقدار قابل توجهی از آبهای زیرزمینی را جمعآوری کرد و به سطح زمین رساند، که همانند چشمههای طبیعی، آب آن در تمام طول سال بدون هیچ ابزار کمکی از درون زمین به سطح زمین جاری میگردد. کاریز که به دست مقنیان ایرانی ساخته شد. این حرفه به همراه خود ساعت آبی و آسیاب آبی را نیز به همراه آورده است. با وجود این که چندین هزار سال از اختراع آن میگذرد هنوز هم این روش استفاده از آب در برخی از روستاها و مناطق مسکونی و کشاورزی و دامداری کشور معمول و متداول است و حتی رکن اصلی کشت و زرع در نواحی خشک است. گوبلو معتقد است که کاریز، ابتدا یک فن ویژه آبیاری نبوده، بلکه به طور کامل از تکنیک معدن نشأت گرفته و منظور از احداث آن جمعآوری آبهای زیرزمینی مزاحم (هرزه آبها) به هنگام حفر معادن بودهاست. اگرچه در گسترهٔ فرهنگی ایران، از معادن مس و احتمالاً روی موجود در کوههای زاگرس، در هزارهٔ دوم قبل از میلاد مسیح بهرهبرداری شدهاست اما این نظر گوبلو چندان علمی بنظر نمی آیدو با مطالعات میدانی در مورد قناتهای ایران همخوانی ندارد خود او نیز بعد نظرش را اصلاح کرده است.
اهمیت قناتها به اندازهای است که سازمان اسناد و کتابخانهٔ ملّی استان یزد به دنبال برگزاری سلسلهنشستهای یزدشناسی خود، نتوانست از کنار قناتها به راحتی عبور کند و موضوع یکی از این نشستهای تخصصی را به قنات اختصاص داد. بر این اساس سومین نشست یزدشناسی با موضوع «یزد، آب، قنات» به همت سازمان اسناد و کتابخانه ملی استان یزد و مرکز قنات ایران با حضور بیش از ۱۰۰ نفر از علاقمندان به تاریخ این دیار برگزار شد.
سیستم استخراج در کاریز طوری است که آب بدون کمک و صرف هزینه فقط با استفاده از نیروی ثقل از زمین خارج میگردد. با توجه به چاهها و کاریزهای موجود، آب کاریز در مقابل آبی که از چاه استخراج میشود، ارزانتر تمام میشود. آب کاریز دائمی است و در مواقع اضطراری کشت و زراعت و در مواقع حساس (نیاز به آب)، قطع نمیشود. منابع آب زیر زمینی توسط کاریز دیر تمام میشوند و استفاده طولانی دارند، هر چند به طور دائم آبها - چه مصرف شوند و چه نشوند - خارج میگردند. کاریز دارای مزایای بسیار زیادی است که در اینجا فقط به تعداد محدودی از آنها اشاره شدهاست. قنات به عنوان یک روش استحصال آب منافع متعددی دارد. اول اینکه بخش عمده کانال آب در زیر زمین قرار گرفته و در نتیجه هدررفت آب بر اثر تبخیر و نفوذ در خاک کاهش پیدا میکند. دوم اینکه نیروی سیستم از طریق جاذبه زمین تأمین میشود و نیازی به پمپ نیست؛ و سوم اینکه از آبهای زیرزمینی به صورت تجدیدپذیر استفاده میشود که مزیّت سوم خود مَزیّتهای دیگری را نیز به همراه دارد .
کاریز، از یک دهانه یا هرنج که روباز است و یک کانال طولی شیب دار زیرزمینی تشکیل شده و چندین چاه عمودی که کانال زیر زمینی سرانجام به سطح زمین مرتبط میسازد، چاهها- که به آنها در موقع حفر، میله هم گفته میشود- علاوه بر کاربرد برای انتقال مواد حفاری شده به روی زمین، عمل تهویه کانال زیرزمینی را نیز انجام میدهند و راه ارتباطی برای لایروبی، تعمیر و بازدید از داخل کاریز نیز به شمار میروند. .</ref> به محل خروج آب قنات مظهر نیز میگویند.
آغاز کاریز همان دهانه کاریز است که «مظهر کاریز» نیز نامیده میشود. مظهر کاریز جایی است که آب از دل کاریز بیرون میآید و ظاهر میشود و میتواند برای آبیاری و دیگر مصارف مورد استفاده قرار بگیرد. قسمت انتهایی کاریز، «پیشکار کاریز» نامیده میشود که در آخرین قسمت آن، چاه مادر کاریز قرار گرفتهاست. قسمتهایی از کاریز که با حفر آنها هنوز آب بیرون نمیآید «خشکه کار» و قسمتی که آبدار است (قسمت انتهایی) قسمت «آبده کاریز» نامیده میشوند.
کندن کاریز و چاههای آن[ویرایش]
کندن کاریز ابتدا با زدن چاه مادر و یا چاهی که آب در آن وجود دارد شروع میشده معمولاً این چاه در پای کوهها و جویبارها و یا محلی که درختان تنومند و انبوه گیاهی داشته کنده میشده است. چون این پوشش گیاهی نشانه وجود آب در زیر زمین بوده است سپس برای انتقال آب مادر چاه به روی سطح زمین کانال حفر میکردند و برای راحتی کار بیرون کشیدن خاک درون کانال و امکان ورود هوا برای تنفس و برای روشنایی چراغ مندو ناچار باید در مسیر چاههای عمودی متعدد کند تا زمانیکه آب به سطح زمین برسد. برای اینکه چاههای قنات در راستای هم قرار بگیرد و پیچ و خم نداشته باشد و باید راستی گرفت و این عمل هم به اینصورت انجام میشده که ابتدا دو تکه سنگ شاقولی را با دو طناب به ارتفاع چاه به عمق چاه میفرستادهاند و در ابتدای پشته سمت چپ این شاقول را نگه میداشتهاند و یه چراغ کاربیت یا مندو را توسط کارگر در انتهای پشته قرار میداده اندو با بستن یکی از چشمان و دقت کردن شاقول با نور چراغ باید در یک راستا قرار بگیرد. چراغ مندو (نوعی چراغ موشی) اولین چراغهایی بوده که دوران باستان استفاده میشده با مندو (روغن گیاه کنتو) روشن میشده؛ و بعدها از چراغ پیهسوز هم استفاده شده اما پی سوز در عمق زیاد خاموش میشده و در قرون معاصر از چراغ کاربیت استفاده شده است.
طول و عمق کاریز[ویرایش]
طول یک رشته کاریز - که در میزان آبدهی آن نیز مؤثر است - نسبت به شرایط طبیعی متفاوت است. این شرایط بستگی به شیب زمین و عمق چاه مادر دارد. از طرف دیگر هر چه سطح آب زیرزمینی پایینتر باشد، عمق چاه مادر بیشتر میشود. مهمترین عاملی که طول کاریز را مشخص میکند، شیب زمین میباشد یک رشته قنات که در میزان ابدهی ان مؤثر است به شرایط طبیعی میزان متفاوت است. این شرایط بستگی به شیب زمین و عمیق ما در چاه دارد. طویلترین قناتی که تا کنون در ایران حفر شده در حوالی گناباد از توابع خراسان است که ۷۰ کیلومتر طول ان است و عمیقترین مادر چاه قناتهای ایران به روایتی ۴۰۰ متر و به روایت دیگر ۳۵۰ متر عمق دارد و ان مربوط به قنات قصبه گناباد است هرچه شیب زمین کمتر باشد طول کاریز بیشتر و هرچه شیب بیشتر باشد طول کاریز کمتر خواهد بود.
نوشتار اصلی: ساعت آبی
از ابتدای اختراع قنات، تقسیم آب بین سهامداران توسط میرآب و با ساعت آبی یا فنجان انجام میشده است. فنجان نیز عبارت است از یک کاسه کوچک با سوراخی در وسط آن و چند درجه با علامت در بدنه داخلی آن که بر روی آبهای یک دیگ بزرگ قرار میگیرد. (در تصویر)
طریقهٔ کار فنجان یا ساعت بدین گونه بوده که میر آب با چشم دوختن به فنجان با هر بار پرشدن و غرقشدن آن و خوردن کاسه به کف دیگ یک فنجان یا هفت دنگ و نیم یا (۷ دقیقه و نیم امروزی) محاسبه نموده و یک سنک کوچک برای هر بار غرقشدن کاسه در یک کیسه یا یک ظرف سفالی میگذاشته است. تا تعداد فنجانها و زمانی که سهامدار قنات آب براب باغ خود یا زمین میبرده را دقیقاً حساب کند مثلاً اگر ۱۰ سنگ درون کیسه باشد یعنی ۱۰ فنجان یا معادل امروزی ۷۵ دقیقه آب قنات را فرد استفاده کردهاست. اگر فردی ۱۰ فنجان سهم از قنات داشته باید (معادل امروزی هفتاد و پنج دقیقه) یعنی مدت زمانی که ۱۰ فنجان آب پر شود آب قنات را به زمین یا باغ خود رها میکرده است و با اعلام جار زدن و یا شیپور زدن یا یک صدای قراردادی فرد بعدی آب را به باغ یا زمین خود منتقل میکرده و به همین ترتیب… معمولاً محل استقرار دایمی فنجان و مدیر آن (میر آب) خانه فنجان بوده است. اما در فصل تابستان گاهی ممکن است فنجان را به محل اصلی تقسیم آب ببرند. کالیستنس مورخ یونانی که در لشکرکشی اسکندر مقدونی به ایران همراه او بود و رویدادهای روز و مشاهداتش را به طور منظم یادداشت میکرد در یادداشتی که بعداً با محاسبات تقویمی معلوم شده که متعلق به سپتامبر ۳۲۸ پیش از میلاد است نوشته است: در اینجا (ایران)، در دهکدهها که آب را بر حسب نوبت به کشاورزان برای زراعت میدهند، یک فرد از میان آنان (کشاورزان) انتخاب میشود تا بر زمان نوبت (و تقسیم زمانی سهام) نظارت داشته باشد. این فرد در کنار مجرای اصلی آب و محل انشعاب آن میان کشاورزان، بر سکویی مینشیند و ظرفی فلزی را که سوراخ بسیار ریزی در آن تعبیه شده است در ظرفی بزرگتر و پر از آب قرار میدهد که پس از پر شدن ظرف کوچک (یک بار و یا چند بار) که به آهستگی و طبق محاسبه قبلی ابعاد سوراخ آن صورت میگیرد، آب را قطع و آن را به جوی کشاورز دیگر باز میکند و این کار دائمی است و این وسیله (ساعت آبی) عدالت را برقرار کرده و از نزاع کشاورزان بر سر آب مانع میشود. .
طبق آمار ارائه شده در کارگاه مهندسی قنات برگزار شده در تهران در سال ۱۳۸۹ تعداد قناتهای فعال ۳۶۳۰۰ رشته بوده و مجموع طول کورههای قنات ۲۱۷۸۰۰ کیلومتر و مجموع طول میلههای قنات ۱۵۸۲۶۸ کیلومتر تخمین زده شده است. قنات زارچ با قدمت بین ۲۰۰۰ تا ۳۰۰۰ سال و با ۷۱ کیلومتر طول به عنوان یکی از بلندترین قناتهای ایران شناخته میشود. عمیقترین مادر چاه نیز در شهرستان گناباد با نام قنات قصبه قرار دارد که تاریخ حفر آن به دورهٔ هخامنشی میرسد. طول قنات قصبه گناباد ۳۳۱۳۵ متر میباشد و عمق مادر چاه رشته اصلی قنات ۲۱۷ متر و عمق مادر چاه رشته انشعابی دولاب نو حدود ۳۰۰ متر میباشد. تنها قنات دو طبقه جهان قنات دوطبقه مون اردستان در محله مون یکی از محلات شهرستان اردستان در استان اصفهان واقع است. این قنات در این محله شامل دو طبقهاست که که در هر طبقه آن آبی مستقل جریان دارد جالب این جاست که آب هیچیک به دیگری نفوذ نمیکند این قنات ۸۰۰ سال پیش احداث شدهاست.
از میان نمونه سفالها و یافتههای سال یابی شده، قدیمترین نمونه به تاریخ ۲۵۰+-۲۲۶۵ و متاخرترین آنها به تاریخ ۴۵+-۷۵۵ سال قبل تعیین قدمت شدهاند. از این رو میتوان ادعا کرد که رشته قنات قصبه گناباد بر اساس یافتههای باستانشناسی حداقل ۲۵۰۰ سال قدمت دارد. از طرفی با توجه به شرایط اقلیمی منطقه و دانستهها، تنها منبع تأمین آب مورد نیاز زیست گاههای باستانی واقع در دشت شمالی گناباد نیز، استحصال آبهای زیرزمینی از طریق فناوری قنات بوده است، بنابراین ما شاهد کهنترین تمدن کاریزی در سطح جهان هستیم.
در زمینهای هموار و نواحیای که زمین شیب کافی ندارد و نیز زمینهای خیلی سست و ماسهای امکان حفر کاریز نیست. آب کاریز، به طور دائم جریان دارد و قابل کنترل نیست. به همین خاطر کاریز مدام باعث تخلیه آب زیرزمینی میشود. در فصولی که به آب احتیاج نیست و یا احتیاج به آب خیلی کم است، امکان جلوگیری از جریان و یا کنترل کاریز وجود ندارد.
کاریز به خاطر این که در سفرههای آب زیرزمینی کم عمق استفاده میشود و این منابع هم غنی نیستند و دارای نوسان زیادی هستند، نسبت به تغییرات سطح آب زیر زمینی خیلی حساسیت دارد. در فصول گرم که گیاه به آب بیشتری نیاز دارد و همینطور در فصول و سالهای خشک، آب کاریز کم میشود. کاریز نسبت به چاه در مقابل سیل و زلزله و امثال اینها آسیب پذیرتر است و خرابی در کاریزها بعضی مواقع طوری است که احیا مجدد آنها یا ممکن نمیباشد و یا از لحاظ اقتصادی مقرون به صرفه نیست.[نیازمند منبع]
سازههای مرتبط با قنات[ویرایش]
آبانبار، حوض یا استخر سرپوشیدهای است که برای ذخیره آب معمولاً در زیر زمین ساخته میشده است. امروزه هنوز تعدادی از آب انبارهای قدیمی باقیماندهاند. در مناطق کمآب و کویری، آب انبار به وسیله آب باران، جویبارهای فصلی، یا آب هدایت شده توسط قنات پر میشد. آب بیشتر در زمستان ذخیره شده و در تابستان مورد استفاده قرار میگرفت. یخچال سازه دیگری است که برای تولید و نگهداری یخ ساخته میشد. یخ در فصول سرد به ویژه زمستان در استخر یخچال درست میشد. پس از تولید یخ، آنها را شکسته و در مخزن (چال) انبار میکردند و در فصل گرما به کار میبردند. برای تهیه یخ در این یخچالها، در شبهای سرد زمستان، آب قناتها یا نهرها به استخر یا حوض یخ بندی که در کنار یخچال قرار داشت، هدایت میشدند. پس از تشکیل یخ در این حوض یخ شکسته و برای نگهداری به درون مخزن یخچال (معروف به پاچال یا چال-یخ) ریخته میشد و در فصل گرما مورد استفاده قرار میگرفت.
سازمان آموزشی، علمی و فرهنگی ملل متحد، یونسکو، اعلام کرد که قنات ایرانی را به عنوان میراث فرهنگی جهانی ثبت کرده است. ۱۱ قنات در مناطق خراسان، یزد، کرمان، اصفهان و استان مرکزی در فهرست آثار جهانی ثبت شدهاند. عمر این قناتها از ۲۰۰ تا ۲۵۰۰ سال است. قنات گناباد، عمیقترین قنات ایران، که عمق چاه اصلیاش به ۳۵۰ متر میرسد، یکی از قناتهای ثبتشده است. همچنین قنات زارچ یزد با طول چند ده کیلومتر و صدها حلقه چاه، یکی دیگر از قناتهای ثبت شده است.
پیوند به بیرون[ویرایش]
"Falaj" redirects here. For other uses, see Falaj (disambiguation).
"Karez" redirects here. For settlements in Aghanistan and Iran, see Kariz.
For other uses, see Qanat (disambiguation).
A Qanāt or karez/kariz (Persian: قنات/کاریز) is a gently sloping underground channel to transport water from an aquifer or water well to surface for irrigation and drinking. Qanat is an old system of water supply from a deep well with a series of vertical access shafts, Qanāts still create a reliable supply of water for human settlements and irrigation in hot, arid, and semi-arid climates. The qanat technology is known to have been developed in Iran by the Persian people sometime in the early 1st millennium BC, and spread from there slowly westward and eastward.
Qanat is the Arabic word for "channel" (قناة). Qanats in Persian called kārīz (or kārēz from Persian: كاريز) (Iran, Afghanistan, Pakistan and Central Asia, derived from Persian: كاهریز), kahan (from Persian: کهن), Kahn (Baloch), kahriz/kəhriz (Azerbaijan); khettara (Morocco); galería (Spain); falaj (from Arabic: فلج) (Emirates and Oman) or foggara/fughara (North Africa). Alternative terms for qanats in Asia and North Africa are kakuriz, chin-avulz, and mayun. Common variants of qanat in English include kanat, khanat, kunut, kona, konait, ghanat, ghundat.
Qanats are constructed as a series of well-like vertical shafts, connected by gently sloping tunnels. Qanats tap into subterranean water in a manner that efficiently delivers large quantities of water to the surface without need for pumping. The water drains by gravity, with the destination lower than the source, which is typically an upland aquifer. Qanats allow water to be transported over long distances in hot dry climates without loss of much of the water to evaporation.
The qanat should not be confused with the spring-flow tunnel, typical to the mountainous area around Jerusalem. Although there are similarities in the construction techniques (both are excavated tunnels designed to extract water by gravity flow), there are crucial differences between the two. Firstly, the origin of the qanat was a well that was turned into an artificial spring. In contrast, the origin of the spring-flow tunnel was the development of a natural spring to renew or increase flow following a recession of the water table. Secondly shafts, which are essential to qanats, are not essential to spring-flow tunnels.
It is very common in the construction of a qanat for the water source to be found below ground at the foot of a range of foothills of mountains, where the water table is closest to the surface. From this point, the slope of the qanat is maintained closer to level than the surface above, until the water finally flows out of the qanat above ground,i.e., the qanat is an underground tunnel, beginning from an underground water source, with a gentle slope made in such a way that water is pulled by gravity to the surface (which is at a lower level than that of the underground water source). To reach an aquifer, qanats must often extend for long distances.
Qanats are sometimes split into an underground distribution network of smaller canals called kariz. Like qanats, these smaller canals are below ground to avoid contamination. In some cases water from a qanat is stored in a reservoir, typically with night flow stored for daytime use. An ab anbar is an example of a traditional qanat-fed reservoir for drinking water in Persian antiquity.
The qanat system has the advantage of being resistant to natural disasters such as earthquakes and floods, and to deliberate destruction in war. Furthermore, it is almost insensitive to the levels of precipitation, delivering a flow with only gradual variations from wet to dry years. From a sustainability perspective, Qanats use the force of gravity to surface up groundwater with no energy requirement and, thus, have low life cycle operation & maintenance costs once built. Qanats transfer freshwater from the mountain plateau to the lower lying plains that have a saltier soil. This helps to control the salinity of soil and prevent desertification.
The value of the qanat
The value of the qanat is directly related to the quality, volume, and regularity of the water flow. Much of the population of Iran and other arid countries in Asia and North Africa historically depended upon the water from qanats; the areas of population corresponded closely to the areas where qanats are possible. Although a qanat was expensive to construct, its long-term value to the community, and thereby to the group that invested in building and maintaining it, was substantial.
Main article: Aqueduct (water supply)
Features common to regions that use qanat technology
The qanat technology is used most extensively in areas with the following characteristics:
Impact of qanats on settlement patterns
A typical town or city in Iran, and elsewhere where the qanat is used, has more than one qanat. Fields and gardens are located both over the qanats a short distance before they emerge from the ground and below the surface outlet. Water from the qanats defines both the social regions in the city and the layout of the city.
The water is freshest, cleanest, and coolest in the upper reaches and more prosperous people live at the outlet or immediately upstream of the outlet. When the qanat is still below ground, the water is drawn to the surface via water wells or animal driven Persian wells. Private subterranean reservoirs could supply houses and buildings for domestic use and garden irrigation as well. Further, air flow from the qanat is used to cool an underground summer room (shabestan) found in many older houses and buildings.
Downstream of the outlet, the water runs through surface canals called jubs (jūbs) which run downhill, with lateral branches to carry water to the neighborhood, gardens and fields. The streets normally parallel the jubs and their lateral branches. As a result, the cities and towns are oriented consistent with the gradient of the land; this is a practical response to efficient water distribution over varying terrain.
The lower reaches of the canals are less desirable for both residences and agriculture. The water grows progressively more polluted as it passes downstream. In dry years the lower reaches are the most likely to see substantial reductions in flow.
Traditionally qanats are built by a group of skilled laborers, muqannīs, with hand labor. The profession historically paid well and was typically handed down from father to son.
The critical, initial step in qanat construction is identification of an appropriate water source. The search begins at the point where the alluvial fan meets the mountains or foothills; water is more abundant in the mountains because of orographic lifting and excavation in the alluvial fan is relatively easy. The muqannīs follow the track of the main water courses coming from the mountains or foothills to identify evidence of subsurface water such as deep-rooted vegetation or seasonal seeps. A trial well is then dug to determine the location of the water table and determine whether a sufficient flow is available to justify construction. If these prerequisites are met, the route is laid out aboveground.
Equipment must be assembled. The equipment is straightforward: containers (usually leather bags), ropes, reels to raise the container to the surface at the shaft head, hatchets and shovels for excavation, lights, spirit levels or plumb bobs and string. Depending upon the soil type, qanat liners (usually fired clay hoops) may also be required.
Although the construction methods are simple, the construction of a qanat requires a detailed understanding of subterranean geology and a degree of engineering sophistication. The gradient of the qanat must be carefully controlled: too shallow a gradient yields no flow and too steep a gradient will result in excessive erosion, collapsing the qanat. And misreading the soil conditions leads to collapses, which at best require extensive rework and at worst are fatal for the crew.
Construction of a qanat is usually performed by a crew of 3-4 muqannīs. For a shallow qanat, one worker typically digs the horizontal shaft, one raises the excavated earth from the shaft and one distributes the excavated earth at the top.
The crew typically begins from the destination to which the water will be delivered into the soil and works toward the source (the test well). Vertical shafts are excavated along the route, separated at a distance of 20–35 m. The separation of the shafts is a balance between the amount of work required to excavate them and the amount of effort required to excavate the space between them, as well as the ultimate maintenance effort. In general, the shallower the qanat, the closer the vertical shafts. If the qanat is long, excavation may begin from both ends at once. Tributary channels are sometimes also constructed to supplement the water flow.
Most qanats in Iran run less than 5 km, while some have been measured at ~70 km in length near Kerman. The vertical shafts usually range from 20 to 200 meters in depth, although qanats in the province of Khorasan have been recorded with vertical shafts of up to 275 m. The vertical shafts support construction and maintenance of the underground channel as well as air interchange. Deep shafts require intermediate platforms to simplify the process of removing soil.
The construction speed depends on the depth and nature of the ground. If the earth is soft and easy to work, at 20 meters depth a crew of four workers can excavate a horizontal length of 40 meters per day. When the vertical shaft reaches 40 meters, they can excavate only 20 meters horizontally per day and at 60 meters in depth this drops below 5 horizontal meters per day. In Algeria, a common speed is just 2 m per day at 15 m depth. Deep, long qanats (which many are) require years and even decades to construct.
The excavated material is usually transported by means of leather bags up the vertical shafts. It is mounded around the vertical shaft exit, providing a barrier that prevents windblown or rain driven debris from entering the shafts. These mounds may be covered to provide further protection to the qanat. From the air, these shafts look like a string of bomb craters.
The qanat's water-carrying channel must have a sufficient downward slope that water flows easily. However the downward gradient must not be so great as to create conditions under which the water transitions between supercritical and subcritical flow; if this occurs, the waves that result can result in severe erosion that can damage or destroy the qanat. The choice of the slope is a trade off between erosion and sedimentation. Highly sloped tunnels are subject to more erosion as water flows at a higher speed. On the other hand, less sloped tunnels need frequent maintenance due to the problem of sedimentation. A lower downward gradient also contributes to reducing the solid contents and contamination in water. In shorter qanats the downward gradient varies between 1:1000 and 1:1500, while in longer qanats it may be almost horizontal. Such precision is routinely obtained with a spirit level and string.
In cases where the gradient is steeper, underground waterfalls may be constructed with appropriate design features (usually linings) to absorb the energy with minimal erosion. In some cases the water power has been harnessed to drive underground mills. If it is not possible to bring the outlet of the qanat out near the settlement, it is necessary to run a jub or canal overground. This is avoided when possible to limit pollution, warming and water loss due to evaporation.
The vertical shafts may be covered to minimize blown-in sand. The channels of qanats must be periodically inspected for erosion or cave-ins, cleaned of sand and mud and otherwise repaired. For safety, air flow must be assured before entry.
Some damaged qanats have been restored. To be sustainable, restoration needs to take into account many nontechnical factors beginning with the process of selecting the qanat to be restored. In Syria, three sites were chosen based on a national inventory conducted in 2001. One of them, the Drasiah qanat of Dmeir, was completed in 2002. Selection criteria included the availability of a steady groundwater flow, social cohesion and willingness to contribute of the community using the qanat, and the existence of a functioning water-rights system.
Applications of qanats
Irrigation and drinking water supply
The primary applications of qanats are for irrigation, providing cattle with water, and drinking water supply. Other applications include cooling and ice storage.
Qanats used in conjunction with a wind tower can provide cooling as well as a water supply. A wind tower is a chimney-like structure positioned above the house; of its four openings, the one opposite the wind direction is opened to move air out of the house. Incoming air is pulled from a qanat below the house. The air flow across the vertical shaft opening creates a lower pressure (see Bernoulli effect) and draws cool air up from the qanat tunnel, mixing with it. The air from the qanat is drawn into the tunnel at some distance away and is cooled both by contact with the cool tunnel walls/water and by the transfer of latent heat of evaporation as water evaporates into the air stream. In dry desert climates this can result in a greater than 15 °C reduction in the air temperature coming from the qanat; the mixed air still feels dry, so the basement is cool and only comfortably moist (not damp). Wind tower and qanat cooling have been used in desert climates for over 1000 years.
The ice could be brought in during the winters from nearby mountains. But in a more usual and sophisticated method they built a wall in the east–west direction near the yakhchal (ice pit). In winter, the qanat water would be channeled to the north side of the wall, whose shade made the water freeze more quickly, increasing the ice formed per winter day. Then the ice was stored in yakhchals — specially designed, naturally cooled refrigerators. A large underground space with thick insulated walls was connected to a qanat, and a system of windcatchers or wind towers was used to draw cool subterranean air up from the qanat to maintain temperatures inside the space at low levels, even during hot summer days. As a result, the ice melted slowly and was available year-round.
Qanats by country
The Qanats are called Kariz in Dari (Persian) and Pashto and have been in use since the pre-Islamic period. It is estimated that more than 20,000 Karizes were in use in the 20th century. The oldest functional Kariz which is more than 300 years old and 8 kilometers long is located in Wardak province and is still providing water to nearly 3000 people. The incessant war for the last 30 years has destroyed a number of these ancient structures. In these troubled times maintenance has not always been possible. To add to the troubles, as of 2008 the cost of labour has become very high and maintaining the Kariz structures is no longer possible.[dubious ] Lack of skilled artisans who have the traditional knowledge also poses difficulties. A number of the large farmers are abandoning their Kariz which has been in their families sometimes for centuries, and moving to tube and dug wells backed by diesel pumps.
However, the government of Afghanistan is aware of the importance of these structures and all efforts are being made to repair, reconstruct and maintain (through the community) the kariz. The Ministry of Rural Rehabilitation and Development along with National and International NGOs is making the effort.
There are still functional qanat systems in 2009. American forces are reported to have unintentionally destroyed some of the channels during expansion of a military base, creating tensions between them and the local community. Some of these tunnels have been used to store supplies, and to move men and equipment underground.
Qanats have been preserved in Armenia in the community of Shvanidzor, in the southern province of Syunik, bordering with Iran. Qanats are named kahrezes in Armenian. There are 5 kahrezes in Shvanidzor. Four of them were constructed in XII-XIVc, even before the village was founded. The fifth kahrez was constructed in 2005. Potable water runs through I, II and V kahrezs. Kahrez III and IV are in quite poor condition. In the summer, especially in July and August, the amount of water reaches its minimum, creating a critical situation in the water supply system. Still, kahrezes are the main source of potable and irrigation water for the community.
The territory of Azerbaijan was home to numerous kahrizes many centuries ago. Archaeological findings suggest that long before the ninth century AD, kahrizes by which the inhabitants brought potable and irrigation water to their settlements were in use in Azerbaijan. Traditionally, kahrizes were built and maintained by a group of masons called ‘Kankans’ with manual labour. The profession was handed down from father to son.
It is estimated that until the 20th century, nearly 1500 kahrizes, of which as many as 400 were in the Nakhichevan Autonomous Republic, existed in Azerbaijan. However, following the introduction of electric and fuel-pumped wells during Soviet times, kahrizes were neglected.
Today, it is estimated that 800 are still functioning in Azerbaijan. These operational kahrizes are key to the life of many communities.
International Organization for Migration and the Revival of Kahriz
In 1999, upon the request of the communities in Nakhichevan, taking into consideration the needs and priorities of the communities, especially women as the main beneficiaries, IOM began implementing a pilot programme to rehabilitate the kahrizes. By 2011 IOM rehabilitated more than 143 kahrizes with funds from the United Nations Development Programme (UNDP), European Commission (EC), Canadian International Development Agency (CIDA), Swiss Agency for Development and Cooperation (SDC) and the Bureau of Population, Refugees, and Migration, US State Department (BPRM) and the self-contribution of the local communities.
KOICA and IOM's Ongoing Kahriz Rehabilitation Project in Azerbaijan
In 2010, IOM began a kahriz rehabilitation project with funds from the Korea International Cooperation Agency (KOICA) which aims to fully renovate a total of 20 kahrizes in the mainland of Azerbaijan. Of these 20 kahrizes, already 16 have been rehabilitated and four are currently under rehabilitation. IOM will complete the works by the end of 2012.
Main article: Turpan water system
The oasis of Turpan, in the deserts of Xinjiang in northwestern China, uses water provided by qanat (locally called karez). The number of karez systems in the area is slightly below 1,000, and the total length of the canals is about 5,000 kilometers.
Turpan has long been the center of a fertile oasis and an important trade center along the Northern Silk Road, at which time it was adjacent to the kingdoms of Korla and Karashahr to the southwest. The historical record of the karez extends back to the Han Dynasty. The Turfan Water Museum is a Protected Area of the People's Republic of China because of the importance of the Turpan karez water system to the history of the area.
There are karez (qanat) systems in Gulburga, Bidar and Burhanpur "(Kundi Bhandara)" as well. The system in Bidar is said to extend two kilometers and originally had 21 vertical shafts. Only 17 shafts are visible today due to builders and developers closing 4. The karez vertical shafts are used by farmers and neighbourhood settlements. The Indian Heritage Cities Network Foundation (IHCNF) led by Valliyil Govindankutty has been working towards conservation of the Karez system. During its survey, IHCNF also discovered a royal bath (Bagh-e-Hammam) probably of the Bahmani period. Local knowledge claims the presence of a terra cotta pipe from the karez mouth to Bagh-e-Hammam.
In the middle of the twentieth century, an estimated 50,000 qanats were in use in Iran, each commissioned and maintained by local users. Of these, only 37,000 remain in use as of 2015.
One of the oldest and largest known qanats is in the Iranian city of Gonabad, and after 2,700 years still provides drinking and agricultural water to nearly 40,000 people. Its main well depth is more than 360 meters and its length is 45 kilometers. Yazd, Khorasan and Kerman are zones known for their dependence on an extensive system of qanats.
Qanats of Gonabad also called kariz Kai Khosrow is one of the oldest and largest qanats in the world built between 700 BC to 500 BC. It is located at Gonabad, Razavi Khorasan Province, Iran. This property contains 427 water wells with total length of 33113 meters. This site were first added to the UNESCO's list of tentative World Heritage Sites in 2007, then officially inscribed in 2016 with several other quants under the World Heritage Site name of "The Persian Qanet".
According to Callisthenes, the Persians were using Water clock in 328 BCE to ensure a just and exact distribution of water from qanats to their shareholders for agricultural irrigation. The use of water clocks in Iran, especially in Qanats of Gonabad and kariz Zibad, dates back to 500BCE. Later they were also used to determine the exact holy days of pre-Islamic religions, such as the Nowruz, Chelah, or Yaldā - the shortest, longest, and equal-length days and nights of the years. The Water clock , or Fenjaan, was the most accurate and commonly used timekeeping device for calculating the amount or the time that a farmer must take water from Qanats of Gonabad until it was replaced by more accurate current clocks. Many of the Iranian qanats bear some characteristics which allow us to call them feat of engineering, considering the intricate techniques used in their construction. The eastern and central regions of Iran hold the most qanats due to low precipitation and lack of permanent surface streams, whereas a small number of qanats can be found in the northern and western parts which receive more rainfall and enjoy some permanent rivers. Respectively the provinces Khorasan Razavi, Southern Khorasan, Isfahan and Yazd accommodate the most qanats, but from the viewpoint of water discharge the provinces Isfahan, Khorasan Razavi, Fars and Kerman are ranked first to forth.
It is Henry Goblot who explores the genesis of qanat for the first time. He argues in his book entitled “Qanats; a Technique for Obtaining Water” the ancient Iranians made use of the water that the miners wished to get rid of it, and founded a basic system named qanat or Kariz to supply the required water to their farm lands. According to Goblot, this innovation took place in the northwest of the present Iran somewhere bordering Turkey and later was introduced to the neighboring Zagros Mountains.
According to an inscription left by Sargon II the king of Assyria, In 714 BC he invaded the city of Uhlu lying in the northwest of Uroomiye lake that lay in the territory of Urartu empire, and then he noticed that the occupied area enjoyed a very rich vegetation even though there was no river running across it. So he managed to discover the reason why the area could stay green, and realized that there were some qanats behind the matter. In fact it was Ursa, the king of the region, who had rescued the people from thirst and turned Uhlu into a prosperous and green land. Goblot believes that the influence of the Medeans and Achaemenids made the technology of qanat spread from Urartu (in the western north of Iran and near the present border between Iran and Turkey) to all over the Iranian plateau. It was an Achaemenid ruling that in case someone succeeded in constructing a qanat and bringing groundwater to the surface in order to cultivate land, or in renovating an abandoned qanat, the tax he was supposed to pay the government would be waived not only for him but also for his successors for up to 5 generations. During this period, the technology of qanat was in its heyday and it even spread to other countries. For example, following Darius’s order, Silaks the naval commander of the Persian army and Khenombiz the royal architect managed to construct a qanat in the oasis of Kharagha in Egypt. Beadnell believes that qanat construction dates back to two distinct periods: they were first constructed by the Persianse, and later the Romans dug some other qanats during their reign in Egypt from 30 BC to 395 AD. The magnificent temple built in this area during Darius’s reign shows that there was a considerable population depending on the water of qanats. Ragerz has estimated this population to be 10,000 people. The most reliable document confirming the existence of qanats at this time was written by Polybius who states that: “the streams are running down from everywhere at the base of Alborz mountain, and people have transferred too much water from a long distance through some subterranean canals by spending much cost and labor”.
During the Seleucid Era, which began after the occupation of Iran by Alexander, it seems that the qanats were abandoned.
In terms of the situation of qanats during this era, some historical records have been found. In a study by Russian orientalist scholars it has been mentioned that: the Persians used the side branches of rivers, mountain springs, wells and qanats to supply water. The subterranean galleries excavated to obtain groundwater were named as qanat. These galleries were linked to the surface through some vertical shafts which were sunk in order to get access to the gallery to repair it if necessary.
According to the historical records, the Parthian kings did not care about the qanats the way the Achaemenid kings and even Sassanid kings did. As an instance, Arsac III, one of the Parthian kings, destroyed some qanats in order to make it difficult for Seleucid Antiochus to advance further while fighting him. The historical records from this time indicate a perfect regulation on both water distribution and farmlands. All the water rights were recorded in a special document which was referred to in case of any transaction. The lists of farmlands - whether private or governmental - were kept at the tax department. During this period there were some official rulings on qanats, streams, construction of dam, operation and maintenance of qanats, etc. The government proceeded to repair or dredge the qanats that were abandoned or destroyed for any reason, and construct the new qanats if necessary. A document written in the Pahlavi language pointed out the important role of qanats in developing the cities at that time. In Iran, the advent of Islam, which coincided with the overthrow of the Sassanid dynasty, brought about a profound change in religious, political, social and cultural structures. But the qanats stayed intact, because the economic infrastructure, including qanats was of great importance to the Arabs. As an instance, M. Lombard reports that the Moslem clerics who lived during Abbasid period, such as Abooyoosef Ya’qoob (death 798 AD) stipulated that whoever can bring water to the idle lands in order to cultivate, his tax would be waived and he would be entitled to the lands cultivated. Therefore, this policy did not differ from that of the Achaemenids in not getting any tax from the people who revived abandoned lands. The Arabs’ supportive policy on qanats was so successful that even the holy city of Mecca gained a qanat too. The Persian historian Hamdollah Mostowfi writes: “Zobeyde Khatoon (Haroon al-Rashid’s wife) constructed a qanat in Mecca. After the time of Haroon al-Rashid, during the caliph Moghtader’s reign this qanat fell into decay, but he rehabilitated it, and the qanat was rehabilitated again after it collapsed during the reign of two other caliphs named Ghaem and Naser. After the era of the caliphs this qanat completely fell into ruin because the desert sand filled it up, but later Amir Choopan repaired the qanat and made it flow again in Mecca.”
There are also other historical texts proving that the Abbasids were concerned about qanats. For example, according to the “Incidents of Abdollah bin Tahir’s Time” written by Gardizi, in the year 830 AD a terrible earthquake struck the town of Forghaneh and reduced many homes to rubble. The inhabitants of Neyshaboor used to come to Abdollah bin Tahir in order to request him to intervene, for they fought over their qanats and found the relevant instruction or law on qanat as a solution neither in the prophet’s quotations nor in the clerics’ writings. So Abdollah bin Tahir managed to bring together all the clergymen from throughout Khorasan and Iraq to compile a book entitled “Alghani” (The Book of Qanat). This book collected all the rulings on qanats which could be of use to whoever wanted to judge a dispute over this issue. Gardizi added that this book was still applicable to his time, and everyone made references to this book.
One can deduce from these facts that during the above mentioned period the number of qanats was so considerable that the authorities were prompted to put together some legal instructions concerning them. Also it shows that from the ninth to eleventh centuries the qanats that were the hub of the agricultural systems were also of interest to the government. Apart from The Book of Alghani, which is considered as a law booklet focusing on qanat-related rulings based on Islamic principles, there is another book about groundwater written by Karaji in the year 1010. This book, entitled "Extraction of Hidden Waters", examines just the technical issues associated with the qanat and tries to answer the common questions such as how to construct and repair a qanat, how to find a groundwater supply, how to do leveling, etc.. Some of the innovations described in this book were introduced for the first time in the history of hydrogeology, and some of its technical methods are still valid and can be applied in qanat construction. The content of this book implies that its writer (Karaji) did not have any idea that there was another book on qanats compiled by the clergymen.
There are some records dating back to that time, signifying their concern about the legal vicinity of qanats. For example, Mohammad bin Hasan quotes Aboo-Hanifeh that in case someone constructs a qanat in abandoned land, someone else can dig another qanat in the same land on the condition that the second qanat is 500 zera’ (375 meters) away from the first one. Ms. Lambton quotes Moeen al-din Esfarzi who wrote the book Rowzat al-Jannat (the garden of paradise) that Abdollah bin Tahir (from the Taherian dynasty) and Ismaeel Ahmed Samani (from the Samani dynasty) had several qanats constructed in Neyshaboor. Later, in the 11th century, a writer named Nasir Khosrow acknowledged all those qanats with the following words: “Neyshaboor is located in a vast plain at a distance of 40 Farsang (~240 km) from Serakhs and 70 Farsang (~420 km) from Mary (Marv) … all the qanats of this city run underground, and it is said that an Arab who was offended by the people of Neyshaboor has complained that; what a beautiful city Neyshaboor could have become if its qanats would have flowed on the ground surface and instead its people would have been underground”. These documents all certify the importance of qanats during the Islamic history within the cultural territories of Iran.
In the 13th century, the invasion of Iran by Mongolian tribes reduced many qanats and irrigation systems to ruin, and many qanats were deserted and dried up. Later, in the era of the Ilkhanid dynasty especially at the time of Ghazan Khan and his Persian minister Rashid al-Din Fazl-Allah, some measures were taken to revive the qanats and irrigation systems. There is a 14th-century book entitled "Al-Vaghfiya Al-Rashidiya" (Rashid’s Deeds of Endowment) that names all the properties located in Yazd, Shiraz, Maraghe, Tabriz, Isfahan and Mowsel that Rashid Fazl-Allah donated to the public or religious places. This book mentions many qanats running at that time and irrigating a considerable area of farmland. At the same time, another book, entitled Jame’ al-Kheyrat, was written by Seyyed Rokn al-Din on the same subject as Rashid’s book. In this book, Seyyed Rokn al-Din names the properties he donated in the region of Yazd. These deeds of endowment indicate that much attention was given to the qanats during the reign of Ilkhanids, but it is attributable to their Persian ministers, who influenced them. . In the years 1984-1985 the ministry of energy took census of 28038 qanats whose total discharge was 9 billion cubic meters. In the years 1992-1993 the census of 28054 qanats showed a total discharge of 10 billion cubic meters. 10 years later in 2002-2003 the number of the qanats was reported as 33691 with a total discharge of 8 billion cubic meters. In the restricted regions there are 317,225 wells, qanats and springs that discharge 36,719 million cubic meters water a year, out of which 3409 million cubic meters is surplus to the aquifer capacity. in 2005, in the country as a whole, there were 130,008 deep wells with a discharge of 31,403 million cubic meter, 33,8041 semi deep wells with a discharge of 13,491 million cubic meters, 34,355 qanats with a discharge of 8,212 million cubic meters, and 55,912 natural springs with a discharge of 21,240 million cubic meters.
A survey of qanat systems in the Kurdistan region of Iraq conducted by the Department of Geography at Oklahoma State University (USA) on behalf of UNESCO in 2009 found that out of 683 karez systems, some 380 were still active in 2004, but only 116 in 2009. Reasons for the decline of qanats include "abandonment and neglect" prior to 2004, "excessive pumping from wells" and, since 2005, drought. Water shortages are said to have forced, since 2005, over 100,000 people who depended for their livelihoods on karez systems to leave their homes. The study says that a single karez has the potential to provide enough household water for nearly 9,000 individuals and irrigate over 200 hectares of farmland. UNESCO and the government of Iraq plan to rehabilitate the karez through a Karez Initiative for Community Revitalization to be launched in 2010. Most of the karez are in Sulaymaniyah Governorate (84%). A large number are also found in Erbil Governorate (13%), especially on the broad plain around and in Erbil city.
In Japan there are several dozen qanat-like structures, locally known as 'mambo' or 'manbo', most notably in the Mie- and Gifu Prefectures. Whereas some link their origin clearly to the Chinese karez, and therefore to the Iranian source, a Japanese conference in 2008 found insufficient scientific studies to evaluate the origins of the mambo.
Among the qanats built in the Roman Empire, the 94 km long Gadara Aqueduct in northern Jordan was possibly the longest continuous qanat ever built. Partly following the course of an older Hellenistic aqueduct, excavation work arguably started after a visit by emperor Hadrian in 129-130 AD. The Gadara Aqueduct was never quite finished and was put in service only in sections.
The acute shortage of water resources give water a decisive role in the regional conflicts arose in the course of history of Balochistan. Therefore, in Balochistan, the possession of water resources is more important than ownership of land itself. Hence afterward a complex system for the collection, channeling and distribution of water were developed in Balochistan. Similarly, the distribution and unbiased flow of water to different stockholders also necessitate the importance of different societal classes in Balochistan in general and particularly in Makoran. For instance, sarrishta (literally, head of the chain) is responsible for administration of channel. He normally owns the largest water quota. Under sarrishta, there are several heads of owners issadar who also possessed larger water quotas. The social hierarchy within Baloch society of Makoran depends upon the possession of largest quotas of water. The role of sarrishta in some cases hierarchical and passing from generations within the family and he must have the knowledge of the criteria of unbiased distribution of water among different issadar.
The sharing of water is based on a complex indigenous system of measurement depends upon time and space particularly to the phases of moon; the hangams. Based on seasonal variations and share of water the hangams are apportioned among various owners over period of seven or fourteen days. However, in some places, instead of hangam, anna used which is based on twelve-hour period for each quota. Therefore, if a person own 16 quotas it means that he is entitled for water for eight days in high seasons and 16 days in winter when water level went down as well as expectation of winter rain (Baharga) in Makran region. The twelve-hour water quota again subdivided into several sub-fractions of local measuring scales such as tas or pad. (Dr Gul Hasan Pro VC LUAWMS .2 day National conference on Kech).
The Chagai district is in the north west corner of Balochistan, Pakistan, bordering with Afghanistan and Iran. Qanats, locally known as Kahn, are found more broadly in this region. They are spread from Chaghai district all the way up to Zhob district.
Qanats were found over much of Syria. The widespread installation of groundwater pumps has lowered the water table and qanat system. Qanats have gone dry and been abandoned across the country.
In Oman from the Iron Age Period (found in Salut, Bat and other sites) a system of underground aqueducts called Falaj were constructed, a series of well-like vertical shafts, connected by gently sloping horizontal tunnels. There are three types of Falaj: Daudi (داوودية) with underground aqueducts, Ghaili (الغيلية) requiring a dam to collect the water, and Aini (العينية) whose source is a water spring. These enabled large scale agriculture to flourish in a dryland environment. According to UNESCO, some 3,000 aflaj (plural) or falaj (singular), are still in use in Oman today. Nizwa, the former capital city of Oman, was built around a falaj which is in use to this day. These systems date to before the Iron Age in Oman. In July 2006, five representative examples of this irrigation system were inscribed as a World Heritage Site.
United Arab Emirates
There are four main oases in the Egyptian desert. The Kharga Oasis is one that has been extensively studied. There is evidence that as early as the second half of the 5th century BC water brought in qanats was being used. The qanats were excavated through water-bearing sandstone rock, which seeps into the channel, with water collected in a basin behind a small dam at the end. The width is approximately 60 cm, but the height ranges from 5 to 9 meters; it is likely that the qanat was deepened to enhance seepage when the water table dropped (as is also seen in Iran). From there the water was used to irrigate fields.
There is another instructive structure located at the Kharga oasis. A well that apparently dried up was improved by driving a side shaft through the easily penetrated sandstone (presumably in the direction of greatest water seepage) into the hill of Ayn-Manâwîr to allow collection of additional water. After this side shaft had been extended, another vertical shaft was driven to intersect the side shaft. Side chambers were built, and holes bored into the rock — presumably at points where water seeped from the rocks — are evident.
David Mattingly reports foggara extending for hundreds of miles in the Garamantes area near Germa in Libya: "The channels were generally very narrow - less than 2 feet wide and 5 high - but some were several miles long, and in total some 600 foggara extended for hundreds of miles underground. The channels were dug out and maintained using a series of regularly spaced vertical shafts, one every 30 feet or so, 100,000 in total, averaging 30 feet in depth, but sometimes reaching 130."
The foggara water management system in Tunisia, used to create oases, is similar to that of the Iranian qanat. The foggara is dug into the foothills of a fairly steep mountain range such as the eastern ranges of the Atlas mountains. Rainfall in the mountains enters the aquifer and moves toward the Saharan region to the south. The foggara, 1 to 3 km in length, penetrates the aquifer and collects water. Families maintain the foggara and own the land it irrigates over a ten-meter width, with width reckoned by the size of plot that the available water will irrigate.
Qanats (designated foggaras in Algeria) are the source of water for irrigation in large oases like that at Gourara. The foggaras are also found at Touat (an area of Adrar 200 km from Gourara). The length of the foggaras in this region is estimated to be thousands of kilometers.
Although sources suggest that the foggaras may have been in use as early as 200 AD, they were clearly in use by the 11th century after the Arabs took possession of the oases in the 10th century and the residents embraced Islam.
The water is metered to the various users through the use of distribution weirs that meter flow to the various canals, each for a separate user.
The humidity of the oases is also used to supplement the water supply to the foggara. The temperature gradient in the vertical shafts causes air to rise by natural convection, causing a draft to enter the foggara. The moist air of the agricultural area is drawn into the foggara in the opposite direction to the water run-off. In the foggara it condenses on the tunnel walls and the air passes out of the vertical shafts. This condensed moisture is available for reuse.
In southern Morocco, the qanat (locally khettara) is also used. On the margins of the Sahara Desert, the isolated oases of the Draa River valley and Tafilalt have relied on qanat water for irrigation since the late 14th century. In Marrakech and the Haouz plain, the qanats have been abandoned since the early 1970s, having dried up. In the Tafilaft area, half of the 400 khettaras are still in use. The Hassan Adahkil Dam's impact on local water tables is said to be one of the many reasons for the loss of half of the khettara.
The Tunnel of Eupalinos on Samos runs for 1 kilometre through a hill to supply water to the town of Pythagorion. It was built on the order of the Tyrant Polycrates around 550 BC. At either end of the tunnel proper, shallow qanat-like tunnels carried the water from the spring and to the town.
The 5,653 m long Claudius Tunnel, intended to drain the largest Italian inland water, Fucine Lake, was constructed using the qanat technique. It featured shafts up to 122 m deep. The entire ancient town of Palermo in Sicily was equipped with a huge qanat system built during the Arab period (827–1072). Many of the qanats are now mapped and some can be visited. The famous Scirocco room has an air-conditioning system cooled by the flow of water in a qanat and a "wind tower", a structure able to catch the wind and use it to draw the cooled air up into the room.
The Raschpëtzer near Helmsange in southern Luxembourg is a particularly well preserved example of a Roman qanat. It is probably the most extensive system of its kind north of the Alps. To date, some 330 m of the total tunnel length of 600 m have been explored. Thirteen of the 20 to 25 shafts have been investigated. The qanat appears to have provided water for a large Roman villa on the slopes of the Alzette valley. It was built during the Gallo-Roman period, probably around the year 150 and functioned for about 120 years thereafter.
There are still many examples of galeria or qanat systems in Spain, most likely brought to the area by the Moors during their rule of the Iberian peninsula. Turrillas in Andalusia on the north facing slopes of the Sierra de Alhamilla has evidence of a qanat system. Granada is another site with an extensive qanat system.
Qanats in the Americas, usually referred to as puquios or filtration galleries, can be found in the Nazca region of Peru and in northern Chile. The Spanish introduced qanats into Mexico in 1520 AD.