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Predicting the stability of armor blocks placed on breakwaters is one of the main challenges in coastal and ocean engineering. However, the armor layer's damage mechanism is very complicated so that there are many uncertainties in the estimation of different parameters in armor design. The inherent uncertainties in these parameters necessitate reliability analysis to ensure the stability of the breakwaters. This study proposed a reliability-based framework for estimating the rock armors weight based on the probabilistic analysis. The effect of different sources of uncertainties in determining effective parameters such as wave height, wave period, water-level changes and armor density was introduced and applied in calculating rock armors weight. Moreover, the correlations between breakwater life span, its probability of failure and stable armor weight were also considered in the analysis. Based on this method, armor weight could be computed according to any desired reliability level and breakwater life span. Results of sensitivity analysis showed that the most critical parameters affecting the reliability of armor weight are wave height and dimensionless damage level. Finally, the presented case study in this article addressed the use of this method in the design of armor weight for a breakwater constructed in the southern part of the Caspian Sea. Results showed that the stable armor weight to maintain a probability of failure equal to 0.005 placed on a breakwater with 50-year life span under a 100-year design storm condition in the Caspian Sea is about 24.28 ton. Moreover, by increasing the breakwater life span from 50 to 100 years, the armor weight increases only by about 10%.

Coastal reservoirs are water storage structures constructed near the river estuary to supply water to coastal areas. One of the most important aspects related to performance of these structures is the effect of reservoir size on the flow and water quality. For this purpose, MIKE3, a 3D numerical software was used in the present work. The case study included proposed coastal reservoir located on the coastlines of the Caspian Sea in the vicinity of Tajan River estuary. To conduct this research, 4 types of reservoirs with different sizes were considered. Input parameters to the model included 5-year flood of Tajan River, initial reservoir salinity and ambient temperature data. The results showed that construction of shallower reservoir due to better surface and depth mixing could achieve higher water salinity during desalinization period. Furthermore, the most water temperature change value was determined after passing hydrograph peak discharge, which shows the effect of inflow on reservoir water quality. Finally, the results of water density revealed that the decreasing trend of water density occurred mostly due to decreasing of water salinity in the reservoir.

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One of the common methods for scour protection around bridge piers is riprap layer. In previous studies, sizing riprap layer was used to ensure 100% protection against scouring. However, in many cases, limited scour depth around a pier may be accepted if only smaller riprap sizes are available. In the present work, the e ects of the smaller size of riprap stones compared to their stable size on the scour depth around a bridge pier were studied. Circular and oval shapes for riprap extent and both round and angular stone shapes were also tested. All tests were conducted at the threshold of bed sediment motion, and the maximum scour depth was measured. The results of these experiments showed that with stone sizes closer to stable riprap material, the e ciency of both round and angular stone shapes was identical. As the size of riprap reduced, deeper scour holes were observed with both round and angular shape materials. The results also indicated that increasing the extent of the riprap layer from circular to oval with 5 times more riprap volume had insigni cant e ects on scour hole for angular shape riprap and, also, reduced the scour hole depth with round shape material. Based on experimental data, a method was developed to calculate a smaller riprap size based on an accepted limited scour hole.

Stable riprap size and optimized extension of the riprap layer around double and triple piers along the flow direction are studied experimentally. Results showed that the critical riprap failure area and stable riprap size around the first pier remain unchanged with increasing pier spacing. In addition, the largest stable riprap should always be placed in front of the first pier in comparison with the remaining downstream piers. However, by increasing the pier spacing, stable riprap size around the second and third pier increased and approached that around the first pier. A relationship was developed for designing stable riprap size in pier groups. Based on this relationship, different riprap sizes are suggested for different zones around the pier group. Experiments showed that the critical zone around the piers includes only a small area and the rest of the riprap extent area can be protected with smaller riprap stones.