الفهرس 
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Abstract
Northern region of Egypt contains five coastal lagoons. Manzalah Lake is the largest natural lake in Egypt. It represents economically important term of fish production. The connections between Manzalah Lake and Mediterranean Sea were created by three straits.These openings are El-Boughdady, El-Gamil and new El-Gamil. Manzalah Lake suffers from very serious environmental water quality problems due to continuous flow of different drains.The main goal of the presented study is to illustrate several solutions and alternatives to be done from a hydraulic view to select the best solution to develop the water circulation. Ten alternatives have been simulated using the 2D surface hydrodynamic model ”IBER” representing the existing situation. For each solution, four scenarios have been simulated describing the combination of cases for minimum and maximum tide range of Mediterranean sea water level to the Lake in addition to the variation of drains discharge into the lake in winter and summer seasons. Ten stations were selected which covered Manzalah Lake while coordinates and measurements from those stations are presented in Table 1. Measurements are (i) water temperature at the time of sampling, (ii) pH value, (iii) electric conductivity (EC), (iv) Total Dissolved Solids (TDS), and (v) Dissolved Oxygen (DO) by using portable devices. Bathymetric survey of the Lake, Water levels at drains outlets and straits, drains monthly discharges have been provided from the Egyptian General Authority for Fishery Resources and Development.This study illustrate the various solutions of the application of the lake model (Iber) to characterize the best solution from the nine hydrodynamics modelling according to the suitable velocity distribution and flow discharge within Manzalah Lake. The nine alternative that have been modelled using IBER software are: (i) Modelling of Manzalah Lake without drains discharge assuming that all drains water will be mixed with El- Salam Canal. (ii) Dredging soil from Lake bed by 1 m and also removing islands form Manzalah Lake. (iii) Dredging soil from Lake Bed by 1 m without islands. In that proposal, the dredged materials will be allocated on the exiting islands for reducing total cost of that solution comparing to the previous suggestion. (iv) Dredging only the existing two straits. (v) Establishing a split channels from straits. (vi) New strait with 200 m width located 16 km at the Western side of the existing strait of El-Gamil. (vii) New strait with 500 m width located 16 km at the Western side of the existing strait of El-Gamil. (viii) New strait with 1000 m width located 16 km at the Western side of the existing strait of El-Gamil. (ix) Constructing weirs at each of drains outlets. The nine alternative solutions of Lake El- Manzalah in this study with the base line case consists of 40 hydraulic model. In each of those ten cases, four hydraulic scenarios have been developed in cases of (i) Minimum tide in summer, (ii) Maximum tide in Summer, (iii) Minimum tide in Winter, and (iv) Maximum tide in Winter.Based on economic analysis of constructing weirs at each of drains outlets seems to be the most feasible suggestion. One case study is reviewed where a type A of PK weirs of control structure was constructed. The application of two design methods on Bahr El Baqar drain helps to increase the discharge capacity and reduce contamination to flow into Manzalah Lake.Results show the feasibility of constructing weirs alternative and a future decision support system should be conducted in order to develop the optimal solution based on economic, social, and environmental criteria in which for each alternative both net benefit and benefit- cost ratio should be evaluated.