فهرست مطالب
مجله پژوهش آب ایران
پیاپی 25 (تابستان 1396)
- تاریخ انتشار: 1396/07/11
- تعداد عناوین: 10
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صفحه 1امروزه استفاده از روش های کم آبیاری، عامل موثری برای صرفه جویی و افزایش راندمان مصرف آب در بخش کشاورزی است. پس در این پژوهش به بررسی اثر اعمال تنش کم آبی در روش کم آبیاری سنتی و کم آبیاری بخشی بر گیاه سیب زمینی پرداخته شده است. بدین منظور رقم آگریا در بهار سال 1391 در مزرعه تحقیقاتی دانشگاه شهرکرد و در قالب طرح بلوک های کامل تصادفی با سه تکرار کشت شد. تیمارهای آبیاری اعمال شده شامل آبیاری کامل و کم آبیاری در سه سطح پتانسیل ماتریک خاک (60-، 80- و 120- کیلوپاسکال) بودند که بعد از مرحله غده زایی و در قالب دو روش کم آبیاری سنتی و کم آبیاری بخشی اعمال شدند. تجزیه و تحلیل نتایج به دست آمده نشان داد کم آبیاری بخشی سبب بهبود وزن خشک اندام هوایی، وزن خشک ریشه، عملکرد بوته و بازار پسندی غده ها شده است. بیشترین مقدار وزن خشک غده نیز در کم آبیاری بخشی با سطح مکش 120- کیلوپاسکال مشاهده شد. کارایی مصرف آب نیز بهبود یافت و بیشترین مقدار کارایی از روش کم آبیاری بخشی با سطح مکش 120- کیلوپاسکال و به میزان 11 /5 کیلوگرم بر مترمکعب به دست آمد که نسبت به نمونه تحت آبیاری کامل 33 /14 درصد افزایش داشت و سبب صرفه جویی 45 /22 درصدی در مقدار آب مصرفی شد.کلیدواژگان: کارایی مصرف آب، کم آبیاری بخشی، تنش کم آبی، سیب زمینی
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صفحه 11جهت درنظر گرفتن ابعاد و پیچیدگی های سیستم های منابع آب، امروزه مدیران و برنامه ریزان برای رسیدن به تصمیمات بهینه، به استفاده از مدلهای بهینه سازی به عنوان ابزاری کارآمد روی آورده اند. در پژوهش حاضر برای بررسی الگوی کشت موجود در دشت همدان- بهار و تدوین سناریوهای مدیریت منابع آب در بخش کشاورزی، از مدل برنامه ریزی خطی و نرم افزار لینگو استفاده شد. این مدل با هدف تعیین الگوی کشت بهینه، تعیین میزان تخصیص بهینه از منابع آب سطحی و زیرزمینی و حداکثر کردن سود حاصل از کشت محصولات تدوین شد و با توجه به قیود و محدودیت ها به اجرا درآمد. به منظور بررسی گزینه های مدیریتی، سه شیوه ی بهینه سازی الگوی کشت در وضع موجود، بهینه سازی الگوی کشت با اعمال محدودیت برداشت از منابع زیرزمینی، بهینه سازی الگوی کشت با تغییر در شیوه آبیاری تدوین و با استفاده از مدل اجرا شد. نتایج به دست آمده از اجرای مدل، حاکی از برتری تغییر شیوه آبیاری نسبت به دو شیوه ی دیگر است؛ به گونه ای که میزان آب مصرفی الگوی کشت 8 /23 درصد کاهش و میزان تولید، سطح قابل کشت و سود به دست آمده به ترتیب 1 /13 درصد، 7 /12 درصد و 8 /15 درصد نسبت به الگوی موجود افزایش نشان می دهد.کلیدواژگان: لینگو، دشت همدان، بهار، مدیریت منابع آب، _ بهینه سازی، برنامه ریزی خطی
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صفحه 21برداشت بی رویه از آب های زیرزمینی در مناطق بیابانی و نیمه بیابانی جهت توسعه اراضی کشاورزی، باعث کاهش کیفیت آب های زیرزمینی گردیده است. از این رو بررسی تاثیر کاهش کیفیت آب بر پیشروی بیابان امری ضروری است. در این پژوهش با استفاده از شاخص های کیفی آب همچون هدایت الکتریکی، مواد جامد محلول، نسبت جذب سدیم و کلر، به بررسی تاثیر کیفیت آب زیرزمینی درروند بیابان زایی دشت مهران پرداخته شد. بدین منظور، از اطلاعات حاصل از 9 حلقه چاه کیفی واقع در دشت مهران طی سه دوره زمانی (83-1380، 87-1384 و 91-1388) استفاده شد. با استفاده از مدل IMDPA و نرم افزار ArcGIS 9.3 ابتدا با وزن دهی به لایه های اطلاعاتی، ارزش هر لایه را در شاخص موردنظر دخالت داده و تاثیر آن بر بیابان زایی مورد بررسی قرار گرفت. بر اساس نقشه های تهیه شده از بین شاخص های مورد بررسی کیفیت آب زیرزمینی، شاخص هدایت الکتریکی تاثیرگذارترین شاخص در افزایش شدت بیابان زایی منطقه است. بر اساس این شاخص در طی دوره های زمانی مدنظر بر شدت بیابان زایی منطقه افزوده شده به طوری که در دوره پایانی 47 /14 درصد منطقه در طبقه بیابان زایی شدید قرار گرفته است. همچنین نقشه بیابان زایی بر اساس شاخص های کیفی آب زیرزمینی در طول این دوره ها نشان می دهد که حدود 72 درصد منطقه در طبقه بیابان زایی کم و ناچیز قرار دارد.کلیدواژگان: هدایت الکتریکی، IMDPA، کیفیت آب، آب زیرزمینی، بیابان، دشت مهران
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صفحه 33فلزات سنگین زیادی از طریق فاضلاب و کارخانجات صنعتی وارد منابع آب می شوند و این منابع را آلوده می کند، از جمله این فلزات سنگین کروم (VI) است که سمی و از عوامل ایجاد سرطان ریه است. در این مقاله حذف یون های کروم (VI) از محلول آبی با استفاده از جاذب زیستی کیتوزان بررسی شد. همچنین تاثیر غلظت کیتوزان، pH و زمان تماس بر توانایی جاذب برای حذف یون های کروم (VI) مورد نظر بوده است. نتایج حاکی از این است که برای نتیجه گیری مطلوب می بایست از غلظت 10 گرم بر لیتر کیتوزان و در pH برابر 4 و در مدت زمان تماس 140دقیقه استفاده شود. با بررسی ایزوترم های جذب، داده های آزمایشی با مدل جذب فروندلیش بهترین انطباق را داشته است. مطالعات سرعت ثابت کرده که مدل سنیتیک درجه دوم بهترین مدل برای توصیف داده های تجربی است.
چکیده (انگلیسی):
Many of heavy metals discharge to water resources through wastewater. One of these heavy metals is Chromium. Two types of Chromium remain stable in the environment. Chromium(III) is a necessary ingredient for human body. But Chromium(VI) is toxic and even causes lung cancer. Industrial activities like plating، cement، steel، cannery and etc. produce large amount of contaminated sewage، so make the wastewater infected. The amount of Chromium(VI) allowed for agricultural water is 0.1 mg/lit. Many experiments include electrochemical deposition، ultrafiltration، ion exchange، reverse osmosis and natural biopolymers have been used to remove Chromium(VI) from sewage. Chitosan has the highest capacity to remove various metal ions. In this study، adsorption of Chromium(VI) ions from aqueous solution using chitosan biological adsorbent was investigated. In these experiments different doses of chitosan 1، 2، 3، 4، 5، 10، 15 and 20 gr/lit were mixed with the different concentration of Chromium(VI) 12.5، 20، 30 and 40 mgr/lit and were shaken for two hours with 450 rpm. The top layer of the solution was transferred to another container and every 20 minutes، concentration of metal ions was measured by an atomic absorption device. Experiments were performed 5 times and then average of the results was used in calculations.
All experiments were carried out at room temperature. The effect of different doses of chitosan at pH 4، 6، 8 at different concentration of Chromium(VI) is 150 minutes has been investigated. After this amount of absorption، no significant effect on removal efficiency of Chromium(VI) ions has been observed. This is due to the coincidence of the active sites in higher concentrations. Hence، some of the ions are affected by adsorbents and some other substances remain in the solution even if more adsorbent is added. There are more ion exchange locations at the higher concentrations of chitosan. The NH3+ chitosan group is primarily responsible for the interaction of the onions and negative charge levels. Therefore according to the above texts، 10 mg/lit is determined as the optimum concentration of chitosan. The pH of solution، because of the metal ions potential، has a significant effect on absorption of heavy metal. Also، the pH affects the concentration of opposite ions in the adsorbent group and ionization degree during the adsorption reaction. The pH of 4-8 was investigated for studying the effect of pH on adsorption of Chromium(VI) ions. The result of experiments showed while the maximum removal occurred at pH 4،the minimum removal of Chromium(VI) ions with chitosan happened at pH 8 . The absorption of Chromium(VI) and other metals، such as Arsenic known as anion، depend on pH. At pH less than 4، the amino group protonated chitosan in varying degrees. The NH3+ group on chitosan is mainly responsible for the removal of Chromium(VI). At higher pH، oxygen functional groups negatively affect the absorbent surface; therefore an electrostatic interaction is produced between the adsorbent and the onions. The effect of contact time on the removal of metal ions with water-soluble chitosan powder was investigated. The removal efficiency reached its maximum value at 140 minutes and thereafter no further deletion occurs until 150 minutes. This may be due to the fact that at the beginning، all occupied areas and the gradient of Chromium(VI) concentration were high، therefore based on these results، 140 minutes were selected for isotherm studies. Quickly removing of Chromium(VI) was increasing from 20-140 minutes. Because at first steps most of sites are potentially empty، as soon as the contact time increase، most of the ions absorb to empty sites. Therefore، finding rest of empty sites is difficult for metal ions. For this reason، the ratio of absorption is decreasing. The presence of most functional group on the surface of chitosan، which requires the interaction between the anions and cations، significantly improves with the bonding capacity، and this process proceeds rapidly. So، contact time is an important parameter treatment system that is cost-effective، therefore، an optimal time of 140 minutes was considered for purification. Absorption isotherms are obtained by plotting the absorbed metal graph versus the equilibrium concentration in the solution. Three model of Temkin، Langmuir and Freundlich were investigated in this paper by chitosan for removing Chromium(VI). Freundlich isotherm is used to absorb the single layer absorbing chemical and the absorption of several layers of physical absorption is based on the assumption of absorbent adsorption on homogeneous surface. According to the result of experiments، the absorption data with Freundlich isotherm was the better fitted with higher correlation coefficient than the other isotherms. This means that the metal has also penetrated the underlying layers and absorption takes place uniformly، therefore، the Freundlich isotherm is a suitable model for describing this absorption behavior. The process to remove Chromium(VI) ions from the liquid phase by absorbing the kinetic models and test speed control mechanism of adsorption، such as chemical reaction، mass transfer and playback controls are explained. Kinetic studies were carried out on various kinetic models such as pseudo-first order، pseudo-second order and intraparticle diffusion model. Pseudo-second order model describes the absorption rate based on the square of the number of occupied spaces on the adsorbent. This kinetic has a higher correlation coefficient than the previous two preceding ones; therefore the absorption rate follows the pseudo-second-order.
In this study، it was concluded that this method is possible to investigate the possibility of using chitosan in water purification and heavy metal removal of Chromium(VI). However، for practical use in the process of water and wastewater treatment for irrigation، performing a technical and economic assessment is necessary and comparing this method with others is recommended.کلیدواژگان: کیتوزان، سنیتیک، ایزوترم فروندلیش، یون کروم (VI) -
صفحه 43کودآبیاری از جمله روش هایی است که نسبت به روش های سنتی پخش کود دارای مزیت هایی از جمله انعطاف پذیری، توانایی توزیع یکنواخت و راندمان کاربرد بالا است. به دلیل محدودیت های زمانی و هزینه های اجرای مزارع آزمایشی، مدل های شبیه سازی کودآبیاری برای رسیدن به وضعیت مطلوب مدیریتی توسعه داده شدند. هدف این مطالعه شبیه سازی غلظت نیترات در رواناب انتهای مزرعه در سامانه آبیاری جویچه ای معمولی، یک در میان ثابت و متغیر با مدل کودآبیاری جویچه ایSURCOS و مدل عباسی و همکاران و مقایسه این دو مدل بود. بدین منظور از داده های مزرعه در دو واقعه کودآبیاری در طول فصل رشد ذرت استفاده شد. مقدار R2، RMSE و NRMSE در شبیه سازی غلظت نیترات رواناب برای مدل عباسی و همکاران و مدل SURCOS به ترتیب 989 /0، 5 /13 میلی گرم بر لیتر و 3 /4 درصد و 913 /0، 0 /17 میلی گرم بر لیتر و 45 /5 درصد به دست آمد. نتایج نشان داد که هر دو مدل توانستند غلظت نیترات در رواناب را به طور موفقیت آمیزی شبیه سازی کنند.کلیدواژگان: شبیه سازی، SURCOS، نیترات، آبیاری سطحی، جریان آب
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صفحه 51اهمیت مدیریت منابع آب، نیاز به مدل سازی دقیق فرآیند بارش و رواناب را در دهه گذشته مطرح کرده است. در این پژوهش برای مدل سازی فرآیند بارش و رواناب از ترکیب مدل ماشین بردار پشتیبان و تبدیل موجک بهره گرفته شده است. بدین منظور سری های زمانی بارش و رواناب با آنالیز موجک به چندین زیرسری با مقیاس های زمانی مختلف تبدیل شده و این زیرسری های زمانی به عنوان ورودی مدل ماشین بردار پشتیبان برای پیش بینی رواناب روزانه درنظر گرفته شده است. نتایج حاصل از صحت سنجی مدل ها بیانگر آن است که بیشترین مقدار ضریب تبیین (R2) و کمترین مقدار جذر میانگین مربع خطا (RMSE) برای مدل منفرد ماشین بردار پشتیبان به ترتیب 69 /0 و 79 /0 و برای مدل ترکیبی ماشین بردار پشتیبان موجکی به ترتیب 92 /0 و 35 /0 است. دلیل برتری مدل ترکیبی نسبت به مدل منفرد ناشی از این است که مدل ترکیبی ماشین بردار پشتیبان موجکی، به جای استفاده از سری زمانی داده های بارش و رواناب در یک مقیاس کلی، از چندین زیرسری پردازش شده زمانی با درجات تجزیه مختلف، به عنوان ورودی در مدل استفاده می کند. همچنین نتایج نشان داد که مدل ترکیبی ماشین بردار پشتیبان موجکی در مقایسه با سایر مدل های ترکیبی مانند شبکه عصبی مصنوعی موجکی (WANN) دارای کارایی و دقت بالاتری است.کلیدواژگان: چند مقایسه ای، تبدیل موجک، درجه تجزیه، ماشین بردار پشتیبان، تابع موجک، خودهمبستگی
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صفحه 61فرسایش خاک یک مشکل جهانی است که به طور جدی منابع طبیعی، رفاه بشر و حتی حیات انسان را تهدید می کند. روش های زیادی برای حفاظت خاک در جهان وجود داردکه این روش ها دارای هزینه زیادی هستند و متناسب با طبیعت نیست. مالچ پاشی یکی از روش های مدیریتی در حفاظت خاک است و سبب کاهش اثرات قطرات باران، جلوگیری از جریان های سطحی و فرسایش خاک می شود. در این میان استفاده از مالچ های آلی سبب بهبود بافت و ظرفیت نفوذپذیری خاک می شوند و از آلودگی محیط زیست جلوگیری می کنند. این مطالعه به بررسی اثر مالچ چوبی گونه توسکای ییلاقی با اندازه طولی 4 سانتی متر و عرض 5 /1 سانتی متر در سه درصد پوشش (0، 30 و 70 درصد) تحت بارانی با شدت 50 میلی متر بر ساعت به مدت 20 دقیقه در پلاتی با ابعاد 2 متر طول، 1 متر عرض و 2 /0 متر عمق در خاک لومی سیلتی پرداخته است. نتایج آزمون LSD و t جفتی در درصد پوشش های مختلف نشان داد که بین پوشش های مختلف در اندازه 4 سانتی متر، در سطح اطمینان 99 درصد در میزان متغیرهای رواناب، بار رسوب، غلظت رسوب و ضریب هرزآب اختلاف معنی دار وجود دارد (01 /0>P) . همچنین میزان فرسایش از 60 تا 97 درصد بسته به میزان درصد پوشش مالچ کاهش یافت. نتایج این پژوهش می تواند برای مدیریت بهتر اراضی جنگلی و همچنین حفاظت خاک مفید باشد.کلیدواژگان: شبیه ساز باران، توسکای ییلاقی، حفاظت آب و خاک، مالچ، _ خرده چوب
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صفحه 71محدودیت منابع آب سبب می شود که مدیریت کم آبیاریبرای افزایش کارایی مصرف آب محصولات کشاورزی درنظر گرفته شود. در این راستا مدیریت های مختلف کم آبیاری به صورت یک در میان متناوب در مراحل رشد در سه بافت مختلف (لوم، لوم رسی و سیلتی رسی) در سه منطقه کرج، فارس و اصفهان بررسی و اثر تلفیقی آن ها برای کاهش مصرف آب و افزایش کارایی مصرف آب برای ذرت دانه ای بررسی شد. نتایج پژوهش در نقاط اجرا و در بافت های مختلف خاک نشان داد که مناسب ترین تیمار از نظر حجم آب مصرفی و عملکرد تولیدی در کلیه نقاط اجرا، مدیریت آبیاری یک در میان متناوب در مراحل مختلف رشد به همراه آبیاری کامل در مرحله گلدهی می باشد. تیمار آبیاری یک در میان متناوب در کل دوره به همراه آبیاری کامل در مرحله گل دهی در بافت لومی، لوم رسی و رسی سیلتی سبب کاهش آب مصرفی به ترتیب برابر 38، 25 و 37 درصد نسبت به آبیاری کامل شد. همچنین کارایی مصرف آب ذرت در این تیمار در مناطق کرج، فارس و اصفهان (با خاک لوم، لوم رسی و رسی سیلتی) نسبت به تیمار آبیاری کامل در کل دوره به ترتیب در حدود 25، 21 و 30 درصد افزایش داشت.کلیدواژگان: آبیاری یک در میان متناوب، مراحل رشد ذرت، کارایی مصرف آب، بافت خاک
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صفحه 79تحلیل پایداری سواحل رودخانه در بسیاری از مدل ها، عمدتا با استفاده از یک ضریب اطمینان به صورت نسبت نیروهای محرک به مقاوم موثر بر سطح گسیختگی، صورت می گیرد. این نیروها توسط مجموعه ای از عوامل کنترل کننده شامل مشخصات هندسی، ژئوتکنیکی و هیدرولوژیکی قرار دارند، تحت تاثیر قرار می گیرند. در این پژوهش، آثار عدم قطعیت موجود در تعیین پارامترهای موثر بر تحلیل پایداری سواحل چندلایه رودخانه ها از نوع چسبنده بر اعتبار نتایج تحلیل پایداری، ارزیابی شده است. بدین منظور از مدل تحلیل پایداری سواحل غیرهمگن رودخانه ها BSTEM استفاده شده و آثار تغییرات هر پارامتر مجزا بر ضریب اطمینان پایداری ساحل در مقابل ساز و کار گسیختگی صفحه ای در شرایطی که مقدار سایر پارامترها ثابت باشد، بررسی شده است. ساحل منتخب مورد بررسی از سواحل در معرض عقب نشینی رودخانه آرنو ایتالیا برگزیده شد. عدم قطعیت های موجود در تخمین پارامترها نیز با توجه به دو منبع اصلی خطا شامل خطاهای اندازه گیری و خطاهای ناشی از تغییرپذیری طبیعت ذاتی هر پارامتر مدنظر قرار گرفت. نتایج این تحقیق نشان داد که به دلیل بزرگ بودن عدم قطعیت های ناشی از تغییرپذیری طبیعت ذاتی پارامترها، احتمال بروز خطا در تخمین ها بسیار زیاد است. در این میان عدم قطعیت پارامترهای ارتفاع، زاویه ساحل، چسبندگی مصالح و رقوم سطح ایستابی به ترتیب دارای درجه اهمیت بیشتری هستند، اما سایر پارامترهای موثر در رابطه، از درجه اهمیت کمتر تا بی اهمیت برخوردار بودند.کلیدواژگان: ضریب اطمینان، سواحل چندلایه، BSTEM، عدم قطعیت، حساسیت، گسیختگی صفحه ای
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صفحه 91سرریزهای پلکانی، از لحاظ اقتصادی، در پایین دست سدهای وزنی RCC توجیه پذیر هستند و مزیت آنها نسبت به سرریزهای هموار میزان بالای استهلاک انرژی در طول سرریز و کاهش ابعاد حوضچه آرامش است. در این پژوهش سه مدل آزمایشگاهی ساخته شده از جنس پلکسی گلاس با شیب های 44 /18، 81 /38 و 2 /50 درجه، تعداد پله های 59، 61 و 65 و همچنین عرض 33 /1، 5 /1 و 12 /2 متر، در موسسه تحقیقات آب وزارت نیرو آزمایش مورد قرار شد. هدف از این پژوهش، بررسی فاصله تاج سرریز تا محل شروع هواگیری طبیعی جریان عبوری در جهت شیب سرریز بود. نتایج این پژوهش نشان داد که افزایش شیب سرریز باعث کاهش طول بدون هوای جریان(l_i) روی سرریز و همچنین هدایت افزایش دبی محل شروع هواگیری طبیعی جریان به سمت پائین دست است. با استفاده از نتایج مطالعه، برای تعیین طول بدون هوای جریان یک رابطه کلی ارائه شده است. مقایسه نتایج، رابطه مناسب تری را برای محل شروع هواگیری طبیعی جریان در این مطالعه نسبت به مطالعات گذشته نشان داد. نتایج این پژوهش بیانگر کاهش طول بدون هوای جریان روی سرریزهای پلکانی در مقایسه با سرریزهای اوجی بود.کلیدواژگان: محل شروع هواگیری، سرریز پلکانی، شیب سرریز، مدل آزمایشگاهی
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Page 1Knowing the effects of various environmental stresses on plant's physiology is necessary to get information about the plant's resistance and survival mechanisms. Drought stress is one of the most common stresses that always threatening agricultural products in widespread parts of the world. Therefore, considering the shortage of water resources, improving water use efficiency in agricultural fields and paying more attention to usage and development of water saving strategies are necessary. As freshwater resources have declined, irrigating crops to meet their full demands are difficult. To reduce the irrigation volume, irrigation techniques such as Deficit irrigation (DI) have been developed meeting the minimum crop water requirement without any significant reduction in crop yield and quality. During the last decade, a novel deficit irrigation strategy named Partial rootzone drying (PRD) has been developed. In PRD one half of the root zone is irrigated while the other half falls dry out. Irrigated and dry sides are periodically switched. PRD irrigation has been tested for different field crops, fruit trees and vegetables. In most cases, PRD irrigation has shown a great potential to increase water use efficiency and to maintain yield. It has been shown that PRD can greatly induce the initiation and growth of secondary roots, which improved the ability of the plant to absorb both water and nutrients from the soil matrix. It seems the combination of irrigation techniques and mechanized irrigation systems such as drip irrigation can significantly improve agricultural water use efficiency.
For this purpose, the effects of deficit irrigation and partial rootzone drying techniques on potato (Solanumtuberosum L. cv. Agria) yield and some components of yield has been studied. This research was done in a field at Shahrekord University in spring, 2012.
The soil texture's field was clay and soil moisture contents at field capacity (FC) and wilting point (PWP) were 37.33% and 15.49%, respectively. A completely randomized block design with seven treatments and three replications was used. Each block (23m × 2.5m) was divided into seven plots. Each plot consisted of three rows of 2.5 m in length. Blocks were bordered by a 1.5m wide protection area.
The tubers were planted on June in rows (75cm between rows and 25cm between tubers). Potatoes were subjected to water treatments Full Irrigation (FI), Deficit irrigation (DI) and Partial rootzone drying (PRD) in three level of soil matric potential (-60, -80, -120 kPa) after tuber initiation. Drip irrigation was used in field and time domain reflectometry (TDR) sensors were used to monitor soil moisture. In FI and DI treatments, one drip line was placed in the center of each ridge. The distance between emitters was 25cm and they were placed near plants. Their discharge rate was 2 (L h-1). In PRD treatment, two drip lines were placed in the center of the ridge. The two drip lines were placed in parallel and emitters distance were 50cm. Some of the physiological and morphological characteristics of the plant were measured in final crop harvest and analyzed by SAS v.9 software. Analysis of variance showed that the difference between irrigation treatments was significant in 1% probability level in most of plants characteristics. Also, with increasing the stress severity, the difference between PRD and DI irrigation was increased. PRD was able to maintain higher biomass production plant under water stress. The results showed that highest and lowest dry biomass was observed in FI (226.49 gr/plant) and DI-120 (187.45 gr/plant), respectively. The maximum and minimum dry weight of root were observed in PRD-120 (8.98 gr/plant) and FI (7.69 gr/plant), respectively. Tubers from each treatment were graded into various size classes and weighed. Among the tuber sizes, the categories of 40-60mm diameter were considered as marketable. Results showed PRD technique increased the marketable yield more than DI.
The maximum and minimum dry matter tuber were seen in PRD-120 (113.03 gr/plant) and DI-120 (98.169 gr/plant), respectively. The maximum and minimum fresh weight of tubers were observed in FI treatment (0.570 kg/plant) and DI-120 (0.430 kg/plant) .the maximum and minimum water use efficiency (WUE) was observed in PRD-120 (5.11 kg/m3) and DI-60 (4.268 kg/m3), respectively. This treatment increased WUE by 14.33%. Also, the obtained results showed that water stress induced in level of soil matric potential (-60, -80 and -120 kPa), reduced water used by 9.85, 16 and 22.45% in field, respectively.
These results showed in comparison to the traditional deficit irrigation strategy (DI) in which the crop is subjected to some degree of water stress, PRD is a successful alternative to FI for saving irrigation water.Keywords: Water use efficiency, Water stress, Partial rootzone drying, Potato -
Page 11Considering the complexity of water resource systems, nowadays managers have widely applied optimization models as efficient tools to reach useful decisions on this issue. The existing optimization models provide new opportunities for better decision making in field of water resources development and planning. Using optimization methods allows decision makers to make the most appropriate decisions among the solutions available for water and soil resources. Optimization is a method by which the best possible answer for a problem is determined according to the target and the existing conjugations, which are specified by functions and mathematical relations. The optimal problem has a target function and several constraints. Math planning is suggested as a useful and efficient way to solve resource allocation problems especially when decision variables, constraints and various parameters are examined. Linear programming is one of the simplest and most practical optimization models. This type of planning can be used for issues with simple relationships such as direct resource allocation to complex operational and management issues. Since all the mathematical relations contained in this model are of the first order type, it is called the linear model.
Hamedan-Bahar plain has faced many problems such as lack of surface water resources, decline of underground water resources and the negative balance of groundwater in the recent years, one part of agricultural land in Hamadan-Bahar Basin is located in Bahar city and the other part in Hamedan city. The water needed for agricultural sector in Bahar city is completely extracted from underground resources while in Hamedan city, about 80% is extracted from underground resources and the rest is supplied by the surface resources. In this region, the first priority is the allocation of water resources for drinking and the second priority belongs to the industrial sector, and agricultural sector is in the third priority. Due to this allocation priority as well as lack of water resources in the region, the water need of crops is not fully ensured according to irrigation scheduling and pattern of cultivation. This research has been tried to compare the different methods of planning, with considering the priorities of water resources allocation and percentage of water supply needs in agricultural sector. Therefore, a linear programming model was created with the goal of 1- determining the optimal cultivation pattern, 2- determining the optimal allocation of surface water and underground water sources, and 3- maximizing the benefit from crop production. This model, based on available water resources and also with considering limitations, determines the cultivation pattern of crops and the amount of water allocated, so the most benefit from crop production will be obtained. Studying the cultivation pattern on this plain and water resources management scenarios, linear program and LINGO software were used. Objective of this model was maximizing of benefit and optimizing allocation of water and cultivation pattern. Evaluating three Scenarios of optimization of cultivation pattern in current situation, optimization of cultivation pattern in changing irrigation method and optimization of cultivation pattern by limiting of groundwater utilization, showed that, the optimization of cultivation pattern in changing irrigation method is better than two others and have more benefits. In this scenario, water consumption of cultivation pattern showed 23.8 % decrease; also, production, area of cultivation and advantage showed 13.1%, 12.7% and 15.8% increase, receptively. The results of this research revealed the necessity of changing the pattern of water consumption in agriculture as an optimal solution to overcome the problems of dehydration and shrinkage of aquifers. Meanwhile, providing social and cultural backgrounds for modifying the pattern of crops by replacing less-water-based products with more economic costs, instead of high-water requirements products, can reduce water use and improve conditions to sustainable use of water resources in the region. Due to the proper allocation of water, demand management and water consumption patterns, especially in the agricultural sector, can create a better and more stable economic situation. Finally, it can be claimed that with the help of planning and optimization models, examining and comparing different methods, making the best decision in the field of water resources management is possible. Eventually, examining other models such as nonlinear planning and applying more limitations and scenarios, especially changes in cultivation pattern, and comparing with the results of this study is suggested.Keywords: Hamedan- Bahar plain, Linear program, LINGO, Water resources management., Optimization -
Page 21Desertification is one of the global phenomena affecting natural resources which occurs not only in arid and semi-arid regions but also in some of the areas in semi-wet regions. Evaluating desertification in a region with vulnerable climate faces unpredictable and damaged conditions plays a significant role in evaluation of the environmental capabilities, prevention of desertification, and restoration and rehabilitation of degraded areas. Destroying the water resources, both their quality and quantity, can lead to decrease in biomass and result in desertification. The decreasing levels of groundwater resources and deteriorating water quality are considered among desertification processes.
Nowadays, groundwater exploitation in arid and semi-arid regions for agricultural lands has increased and subsequently over-exploitation of these sources has degraded groundwater quality. Therefore, investigating the groundwater quality and its effects on the increasing rate of desertification intensity is a necessary task. In this research, the effects of groundwater quality on the desertification in Mehran plain have been investigated by employing water quality parameters including electrical conductivity, total dissolved solids, sodium adsorption ratio, and chloride using the Iranian model of IMDPA.
In the IMDPA model, a weight ranging from 1 to 4 was assigned to each layer based on its influence on desertification according to literature reviews and researches performed by other researchers and geographical condition of the Mehran plain. Value 1 and value 4 indicate the best and the worse conditions of desertification, respectively. Numerical values of produced indices were transformed to thematic maps in ArcGIS Desktop 9.3. In order to determine the current quality of water in Mehran Plain, the data obtained from 9 quality wells located in the area have been used and analyzed over three time periods (2001-2004, 2005-2008, and 2009-2012). Then, to investigate the desertification intensity of Mehran Plains based on the IMDPA model, the criterion of water quality was used. After determining the numeral value of each parameter, the standard numerical value is determined based on the geometrical average of the selected criteria.
The information layers related to each index and criterion for all the three periods were prepared using interpolation and weighting methods in GIS. After preparing the related layers for the criterion of water quality in selected wells, the measures were combined in Arc GIS 9.3 software application to obtain the final map for the desertification status of the region for all the three selected time periods. Finally, they were classified in desertification classes of low, medium, intense, and severe intensification.
The results show that the indices of chloride and sodium absorption ratio due to their locations in the low desertification class and quantitative value of less than 1.5 are not very effective on the intensity of desertification in the region. Based on the results, the amount of chloride and the sodium absorption ratio over the entire study region during the recent years have not fluctuated significantly, so that many of the areas are classified as low desertification and the effects of this index are not readily visible in this region. The total dissolved solids show a greater change compared to chlorine and sodium absorption ratios in the last period in so that based on this index, during the two first periods, the region is classified as low desertification while in the last period, due to higher concentration of these substances, the region is classified as mild desertification. The desertification intensity map of Mehran Plain based on the index of electrical conductivity shows that the intensity of desertification from the beginning of the period has been increased towards the end of the period in a way that 8.95 percent of the region in the first period is classified as intense desertification and in the last period, the extent of this area reaches 14.47 percent of the entire region. Moreover, the desertification map based on the indices of groundwater quality during these periods shows that almost 72 percent of the region is classified as low and negligible desertification.
Decreasing of ground water levels caused by digging multiple wells has led to an increased electrical conductivity of the water from these wells as well as their salinity. Intense decline of water level due to uncontrolled withdrawal and other factors such as climate change, drought, and irrigation methods have increased the water salinity, which in turn increases the salinity of the soil in the study area.
The results obtained from evaluating the average weight of the quantitative values of the selected indices for the water quality showed that in the studied region, the average weight of the criterion of water quality is in negligible and low desertification class. Among the indices assessed for water quality, the obtained value (the score) for the electrical conductivity is higher than those for other measures, so, it has more effects on increasing the desertification intensity in the region regarding the quality of water criterion (i.e. it has caused a rise in the final amount of desertification since the value of each criterion is obtained from the geometric average of the numerical values and the value of the total desertification score is obtained based on the geometric average of the numerical value of the criteria). Hence, the electrical conductivity index is the most important index in the desertification of the region.
Considering the fact that one of the reasons behind higher electrical conductivity is the low level of water, uncontrolled withdrawal should be avoided in this region as well as similar regions all over the country by making the wells smart using devices such as electronic cards for water withdrawal. In other words, after withdrawing a predefined quantity, there must be a power outage so that nobody can withdraw any more water. At the moment, unfortunately there are several unauthorized wells withdrawing water in all regions in the country which lead to decrease in levels of groundwater and caused aquifers go dry. Hence, as a recommend these unauthorized wells should be closed since preventing uncontrolled withdrawal is one of the effective ways to solve the water crisis.Keywords: Water quality., Desert, Electrical conductivity, Mehran plain, IMPDA, Groundwater -
Page 43Surface fertigation in furrow irrigation has potential to decrease water and fertilizer losses. Fertigation is as a technique having more advantages than conventional fertilizer application methods such as flexibility, potential for improving fertilizer distribution uniformity and high application efficiency. Due to time restriction and experimental field implementation cost, fertigation simulation models have been developed to achieve the desired management conditions. Research has been performed in the last decades to out for simulate surface water and solute flow under surface fertigation. These researches reported that simulation could be effectively applied to improve surface fertigation design and management, reducing water and fertilizer losses. Playan and Faci (1997) stated that a short duration of the fertilizer injection resulted in low fertilizer distribution uniformity in border fertigation. However, Sabillón and Merkley (2004) advocated relatively short injection times and relatively high injection rates in furrow fertigation. Abbasi et al. (2003) conducted a blocked-end furrow fertigation experiment and simulated overland water flow and solute (bromide) transport. These authors reported that high solute uniformity was obtained when the solute was applied during the entire irrigation event or during the second half of the irrigation event. Burguete et al. (2009) presented a fertigation model, named SURCOS, for furrow (and level furrow) irrigation. Model simulations succeeded in predicting fertilizer concentration in irrigation water at different times and distances along the furrow for different fertilizer application strategies. The objective of this study was to simulate nitrate concentration in runoff in conventional, variable alternate and fixed alternate furrow irrigation regimes by SURCOS fertigation model and Abbasi et al. model and comparison of these two models. For this purpose, experimental field data were used in the two fertigation events during maize growing season.
A field experiment was conducted in the experimental station of College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. This zone has a semi-Mediterranean climate with an average annual rainfall of 265 mm and an average annual temperature of 16 ◦C. Three furrow irrigation methods; conventional, variable alternate, and fixed alternate furrow irrigation (CFI, AFI and FFI, respectively) were investigated in this work. Inflow and outflow (runoff) rates were measured by WSC flume installed at the inlet and outlet of the experimental furrows. The experimental furrows were marked for measuring the water advance times. The average basic infiltration rate (f_0) was determined by the inflow-outflow method (Elliot and Walker 1987). The two-point method (Elliott and Walker 1982) was also used to determine the Kostiakov-Lewis parameters, coefficients a and k. The Mannings n was assumed to be 0.04. Two different numerical models (Abbasi and SURCOS) were used and assessed for the simulation of the surface fertigation which both are capable of simulating overland water flow and solute transport. The governing equations for water flow were solved in the form of a zero-inertia model of the Saint-Venants equations. Also, Solute transport was modeled with the advection-dispersion equation.
Both models were run for the first and second fertigation events regarding the input data. The runoff nitrate concentrations were predicted and compared with the measured data. The predicted nitrate concentrations were almost constant whereas the measured values were relatively fluctuating. These variations could be related to spatial variability in soil infiltration and roughness properties and small changes in water and fertilizer rates in the field. Having high solubility and mobility, nitrate could easily move with water. There were good agreements between the measured and predicted nitrate concentrations. The R2, RMSE and NRMSE values for simulation of nitrate concentration in runoff were obtained 0.989, 13.5 mg/L, 4.3 % for the Abbasi et al. model and 0.913, 17 mg/L, 5.45 % for the SURCOS model, respectively. The results indicated that both models were able to successfully simulate nitrate concentration in runoff.
Although the water and fertilizer movements in furrow irrigation are bi-dimensional, both 1D surface fertigation models could successfully simulate the fertigation process. However, the Abbasi model had relatively better performance than the SURCOS model due to the less error in predicting nitrate concentration while the SURCOS model could better distinguished differences of the irrigation treatments. The results indicated that the simulation models can be used to get better design and management of the fertigation in alternate and conventional furrow irrigation for alleviating the water crisis and environmental risks.Keywords: Surface irrigation, SURCOS, Water flow, Simulation, Nitrate -
Page 51The most important factor in improving the environmental planning and hydrological management decisions is introduced as the modeling and exact simulation of rainfall and runoff processes. The accurate and exact modeling of hydrological processes such as rainfall-runoff can give impressive information for urban planning, land use, flood and water resources management for a given watershed. Also, in order to mitigate drought impacts on water resource systems, the management attempts are based on hydrological process modeling. So, the need for accurate modeling of the rainfall-runoff process has grown rapidly in the past decades. Recently, new techniques in Artificial Intelligence (AI) like Support Vector Machine (SVM) have been used by hydrologists.
New techniques on AI, with a great variety of applications, have been recognized over the past decade. One of them is the SVM which is used in the classification and regression algorithms assortment. Support Vector Machines (SVMs) are kernel machines useful for classification and regression problems. The SVM model is based on the statistical learning theory. This model is a supervised learning technique that provides the input-output mapping functions with respect to a set of training data. The advantage of SVM modeling in comparison with the other methods is that this modeling works with less training data and variables. Compared to a traditional neural network, the SVM method replaces traditional empirical risk with structure risk minimization and solves a quadratic optimization problem which can get the optimal global solution in theory. In this paper, the wavelet analysis was linked to the SVM model concept for modeling Aghchai watershed rainfallrunoff process. To do this, the main time series of two variables, rainfall and runoff were decomposed to some multi-scale time series by wavelet theory. On the other hand, the annual or seasonal data were decomposed into large-scale approximation subsignals and daily data in small periods were decomposed into the detailed sub-signals; then, these decomposed rainfall and runoff data act as the inputs of SVM to predict the daily runoff discharge. As a result, the runoff discharge was forecasted about 1 day ahead. To reach this aim, the classical SVM was first used for data modeling. The Kernel function was employed for data classification in the SVM. There were various kinds of Kernel functions. In this paper, the SVM modeling was done by three kinds of Kernel functions with respect to rainfall and runoff data concerning Aghchai watershed. Afterwards, some input combinations (combs. 1-5) were used as the inputs of SVM model; then, the performance of each combination was measured. The most significant part of the study occurred when the wavelet transform was combined with the SVM. So, the single SVM modeling gets promoted by the wavelet transform. In this step, the time series of each watershed were calibrated and verified by the Wavelet-Support Vector Machine (WSVM) model with the different kinds of mother wavelet types including Haar, db2, sym1 and coife1 and different decomposition levels (1-4).
The obtained results indicated that the RBF-Kernel function has the highest efficiency as compared to Poly and MLP Kernel functions for both watersheds. So, the RBF-Kernel function was employed in next steps. The comparison results of data combinations showed that the combination (2) has a better compatibility as the SVM input for both watersheds. Finally, in the WSVM model, the db2 mother wavelet and the decomposition level 3 were selected as high-efficiency ones for both watersheds and their calibration and verification results were illustrated in the given figures. So the maximum value of determination coefficient (R2) and the minimum value of root mean square error (RMSE) in verification for the SVM model was 0.69 and 0.79, respectively and for the WSVM model was 0.92 and 0.35, respectively. As a result, the proposed hybrid model was relatively more appropriate because the WSVM model uses some multi-scale processed time series with different resolution levels as inputs to model instead of using raw rainfall-runoff data time series. Also, the WSVM model had a high performance to predict the peak values of runoff discharges by considering seasonality and multi-scale time series. Finally, studying compatibility of the model with other river's data, the hybrid WSVM model caused accurate results for the watershed of Eel-River, located in California State. Also, WSVM model showed better performance in comparison with the other hybrid model such as Wavelet-Artificial Neural Network (WANN).Keywords: Wavelet transform, wavelet function, Support vector machine, Decomposition degree, Auto regressive, Multi-scale -
Page 61Soil erosion is a global problem that seriously threatening natural resources, human welfare and even life human. Globally, there are many methods for soil conservation including biological, mechanical and bio-mechanical methods, which these methods are expensive and they are not environmental friendly. Mulching is one of the management practices to reduce the impact of raindrops on soil erosion and control surface runoff. From these, organic mulches improve soil texture and infiltration capacity and avoid from environmental pollution. Mulching also decreases crusting of the soil due to rainfall impact also reduces erosion by absorbing the kinetic energy of the raindrops. Wood mulches have been developed from wood manufacturing waste (e.g., wood strands such as Wood Straw, wood shreds or wood chips) made from burned trees or forest thinning operations, and shredded forest floor material from nearby eroded areas. Although these wood-based mulches are unlikely to harbor non-native seeds, their greater density can increase the cost of transportation to the site and aerial application as compared to straw mulch. Laboratory studies established that wood strands have greater resistance to wind displacement as compared to agricultural straw, and both wood strands and wood shreds provide equal or greater protection from erosion as compared to agricultural straw mulch at equal areal coverage rates. Foltz and Wagenbrenner (2010) reported that a 50% cover of wood shred mulch, with small (Keywords: Soil, water conservation, Alnussubcordata, Wood shreds, Mulch., Rainfall simulator
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Page 71Using deficit irrigation management has an important role in increasing water use efficiency in areas that are faced with water shortage. Alternate furrow irrigation is one of the deficit irrigation strategies which improve water use efficiency without significant effect on crop production. Results of different research demonstrated that alternate furrow irrigation has been widely used to reduce water use up to 50%. Application of integrated management of irrigation as alternate furrow irrigation at the critical growth stages of maize can be used both to save water and increase water use efficiency. So, this management with regard to the critical stages of maize development in different regions (with different soil textures, including loam, clay loam and silty clay)was studied, Also, combined effects of reducing water consumption and increase water use efficiency were investigated.
This research was conducted in Soil and Water Research stations (Karaj, Darab and Isfahan) for 2 years. The randomized complete block design with three replications was considered in this research project. Irrigation timing was determined based on allowable depletion of soil moisture (50% deficit) and irrigation water depth was considered based on refilling soil moisture content till field capacity in rootzone for all treatments. In this regard, irrigation management was conducted in six treatments, included: (T1) full irrigation in total period (Control); (T2) alternate furrow irrigation in total period; (T3) full irrigation in development stage and irrigation during an alternating among other stage; (T4) full irrigation in flowering stage and alternating irrigation in other stage; (T5) full irrigation in development and flowering stage and alternating irrigation among other stage; (T6) full irrigation in flowering and getting stage and alternating irrigation among other stages. The treatments were done in different areas with different soil textures (The soil textures of Karaj, Darab and Isfahan were Loam, Clay loam and Silty Clay, respectively). Water use efficiency index expresses the relation between obtained yield and total amount of water applied. In this research, variation between irrigation treatments on maize production including dry biomass, grain yield and water use efficiency has been demonstrated.
Results in all locations showed that irrigation treatments have significant effect on dry biomass, grain yield and water use efficiency of maize. Using alternate furrow irrigation management in other growth stages with full irrigation in flowering stage (T4) for Clay, Clay loam and Silty clay soil textures, respectively decreased water consumption by 38, 25 and 37%. Grain maize production in full irrigation treatment (T1) was about 9510 kg/h in loam soil (Karaj). Statistical analysis showed that T2 (with 5850 kg/h of grain yield) and T3 (with 6090 kg/h of grain yield) treatment were in the same group but T4, T5 and T6 (with respectively 7563, 8040 and 7770 kg/h of grain yield) were located in another group that produced higher grain yield than T2 and T3 in Karaj site with loamy soil. Also, results in Darab with Clay loam soil showed that grain yield of control treatment (T1) was 9412 kg/h. Grain yield reduction in T4 treatment (full irrigation in flowering stage and alternating irrigation in other stage) was about 10% comparing to the control treatment in Darab site. While, application of alternate furrow irrigation in all stages of maize, decreased the grain yield about 19 %, comparing to T1. In Isfahan, results showed the significance difference between irrigation treatments on grain yield. The maximum grain yield was about 8690.3 kg/h in control treatment and the minimum of grain yield was related to T2 treatment (alternate furrow irrigation in total period), which was about 6848.8 kg/h. In this site with silty clay soil texture, the grain yield of T2, T3, T4, T5 and T6 were decreased about 21,18,16,14 and 12%, respectively. Considering T4 in all sites, water use efficiency increased as 25, 21 and 30% in the soil textures of Loam, Clay loam and Silty Clay, respectively. Using alternate furrow irrigation management in other stages with full irrigation in flowering stage (T4) decreased water application about 35% and increased water use efficiency about 25%, in average, comparing to the full irrigation treatment. The most critical stage of maize, that is better to be fully irrigated, is flowering so we can use alternate furrow irrigation in the other growth stages except flowering (Full irrigation in flowering stage for more water saving and achieving higher water use efficiencies). This reflects the importance of full irrigation at critical stages of flowering and ripening. Hence, with this irrigation management, we can increase cultivated area and achieve more total yield with higher water use efficiency. Therefore, alternate furrow irrigation is a valuable strategy for dry region, where water is the limiting factor in crop cultivation.Keywords: Alternate furrow irrigation, Water use efficiency, Maize, soil texture -
Page 79Rivers have not always flowed in the same directions as they do today. They constantly change their route, for various reasons. Therefore, understanding of river pattern changes, especially near cities, roads and coastal infrastructures is the most important issue. Hence, it is essential to assess unstable banks condition by applying riverbank stability analysis models which will lead to better understanding of the movement pattern of rivers course, so its results can be used to accurately model the flow and sediment transport along the river's route. Nevertheless, access to all required data for the riverbank stability analysis along the entire course of river is very difficult and practically impossible due to the complexity of the different mechanisms of bank erosion. In previous studies, evaluation of uncertainty in the analysis of bank stability has been done with the assumption of homogeneity of materials forming the riverbank, while such stream banks are rarely found in nature. The aim of this study is to evaluate the effect of parameter uncertainty arising from the variability of input parameters influencing the stability analysis of composite banks on the reliability of the simulated factor of safety for planar failure.
The area selected for this study is located in Arno River, Italy (referred to as the reference bank) and it has been subjected to bank retreat. Among various types of riverbank failure, planar failures are the most common type, being associated with steep, relatively low banks composed of cohesive sediments. Moreover, this type of failure represents the most frequent mechanism observed on fine-grained banks along the Arno River. In this paper, the bank stability and toe erosion model (BSTEM), developed by Simon et al. (2006) has been used. BSTEM is a steady-state bank stability model capable of analyzing the stability of non-homogenous bank materials that calculates a bank factor of safety for multi-layer stream banks. The model uses two different limit equilibrium algorithms to calculate factor of safety (FS) for multi-layer stream banks using data from the bank geometry, geotechnical properties and hydrological conditions. At the highest level, two sources of uncertainty exist: uncertainty due to variability and uncertainty due to limited knowledge. Uncertainty due to variability first as these uncertainties ultimately combine to contribute to uncertainty due to limited knowledge. Five distinct subclasses of uncertainty due to variability are proposed: inherent natural randomness; value diversity (socio-political); behavioral diversity; societal randomness and technological surprise. Inherent natural randomness is attributed to the nonlinear, chaotic and unpredictable nature of natural processes. The natural variability of river systems should be a fundamental consideration in integrated river basin management and restoration
In these sensitivity analyses, the parameter value ranges (PR) that induce less than a ±15% change in the simulated factor of safety (relative to the reference bank) are highlighted by the grey-shaded areas. The ±15% threshold is arbitrary but is selected to enable direct comparison with the study performed by Samadi et al. (2009) for a homogenous bank. The shaded areas thus delineate the parameter variations (relative to the reference bank) that have a relatively minor influence on the simulated factor of safety. In fact Samadi et al. (2009) used the relationship between Parameter Range (PR) and parameter uncertainty (PU) to determine the overall influence of parameter uncertainty on the reliability of homogenous bank stability modeling. To compare their results to non-homogeneous riverbanks, just these contractual relationships were used. This was achieved by defining four categories to describe each parameter's influence on reliability: (i) insignificant (PU>PR). The sensitivity analyses results and variations in the factor of safety values due to the variation of the effective parameters on bank stability in the aforementioned threshold were considered in this study.
As we reported, bank height and bank angle are both very important while the impact of parameters uncertainty of the tension crack depth, river flow depth and matric suction angle are insignificant on the reliability of the bank stability results in both homogeneous and non-homogeneous riverbanks. However, other factors show some differences between the studied composite riverbank (Arno River) results and the results obtained from analysis of homogeneous bank in the study of Goodwin Creek by Samadi et al. (2009). For example, unlike the previous case studies (homogenous bank), the bank material cohesion in both layers of Arno River is of less importance, seems to be due to the less cohesiveness of bank materials in the current study rather than the previously studied homogeneous bank. Similarly, it has been indicated that soil unit weight is not important and shows this parameters insignificant impact on predictive reliability of the calculated factor of safety values. Another important issue is the higher importance and sensitivity of the upper than lower bank to simulate bank stability factor of safety which is completely obvious in the role of the internal friction angle in the upper bank rather than the lower bank and also homogeneous riverbank materials. In addition, groundwater levels are another important parameter under the specific conditions of the present study.Keywords: Composite riverbanks, Uncertainty, Planar failure, Factor of safety, BSTEM, Sensitivity -
Page 91One of the hazards which almost always threaten dam spillways is the cavitation phenomenon which is caused by high-velocity flow hydrodynamic effects on the structure. Presence of air in high-velocity flow can prevent the dangers of cavitation or at least reduce them. Stepped spillways with considerable applications have been economically justified the downstream of RCC weight dams. Superiorities over smooth spillways include high rate of energy dissipation along the spillway and reduction in stilling basin dimensions.
The most important indexes of the flow passing the stepped spillways are the high level of turbulence and the way air enters the flow. Turbulence fluctuations near the water-air free surface (two-phase flow) create air bubbles. Generally, turbulent flow is present in the vicinity of boundary layer which begins from the crest, develops downstream and crosses the water surface. When outer edge of the boundary layer reaches the free surface, turbulence occurs and causes a natural aeration of the flow. Air entrance location is called the inception point. In the downstream, the flow is fully developed and there is accelerated aeration in the free surface.
In these spillways, aeration length which is defined as the distance between the crest to the inception point can be exposed to cavitation. The boundary layer thickness has been estimated by different researchers for spillways without any step but it is not accurately determined for stepped ones. The reason is due to the complexity of flow conditions in these kinds of spillways.
Inception point location in most cases is obtained by observation. Therefore, the specifications and coordinates presented for this point by different researches have a wide range of discrepancy. Classically, this point conforms to a cross section of the step in which the water flow has a white or milky color. In this experimental study, three models were used at Water Research Institute of Ministry of Power. Plexiglas was applied in the models for stepped spillways with 18.44, 38.81 and 50.2 degrees tangents. The step numbers were 59, 61 and 65 and they had 1.33, 1.5 and 2.12 meters width, respectively.
The objective was to investigate the distance between the crest and the inception point along the spillway tangent, so the inception point was determined by passing different amount of mass flow rates on different experimental models. It is worth mentioning that the minimum and maximum amount of mass flow rate, required to record the flow inception point, are not the same for the three models since they are based on model width and its tangent. By increasing the tangent and its width, the mass flow rate will be higher for a continuous flow to be established.
According to the results obtained, increasing the spillway tangent would bring the inception point closer to the crest. In other words, it would delay the flow. Considering the model specifications of this study, an equation is extracted which is applicable for a wide range of angles. To do this, taking the Froud number (F_*) and spillway tangent as variables, the following relation is obtained:l_i/k_s =11.08 〖F_*〗^0.675 〖(tan〖θ)〗〗^(-0.2114) R^2=0.87 (1)
This equation is valid for the range of 〖18〗^°≤θ≤〖52〗^°.
A comparison between above equation with the Woods relation for ogee spillways in model number 2 with mass flow rates in the experiments showed that the length without air in stepped spillways was less than the length in ogee spillways. Consequently, the inception point was closer to the crest. Also, a comparison was performed between the recommended relation and Chanson and Boes relations. The reason of selecting these two relations was the wide range of angles they conclude. Results showed that the presented equation had the smaller standard error with respect to the abovementioned relations.
Generally, the results show that a stepped spillway will bring the inception point closer to the crest in comparison with smooth and ogee spillways i.e. l_i will be smaller in these kinds of spillways. Implementing a quantitative comparison between the Wood's relation and the equation obtained in this study shows that l_i can be reduced up to 5-10%, depending on the mass flow rate. Increasing the mass flow rate in these spillways which promotes the Froud number (F_*), will increase the aeration length and cause a delay in aeration process. This means that F_* has a direct relationship with l_i. Results also show that increasing the spillway tangent will reduce l_i and bring the inception point closer to the crest. Consequently, equation 1 which verifies the abovementioned discussion was derived with an acceptable correlation coefficient.Keywords: Spillway tangent, Stepped spillway, Air inception point, Experimental model
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