Irrigation and Drainage Structures Engineering Research
Year:2018 | Volume:19 | Issue:70 |Papers Count:9

Roodasht irrigation network is placed at downstream of Zayanderood River. A recent problems in the operation of the network is inflow fluctuations in the main canal because of flow variations at upstream of the river. Thus, enhancing utilization of operational condition of the main canal becomes essential. In this study, the operational performance of the LAT proportional weirs under inflow fluctuations was investigated and compared with the Nyrpic Module Off-takes for a realistic operational period of time. To achieve the mentioned objectives, mathematical models of the both systems were developed and their operational performance was evaluated within equity, adequacy, and efficiency of water delivery point of views. With regards to the obtained results, both systems showed a more or less same performance from of adequacy and efficiency in upstream and downstream off-takes. Comparing the calculated equity performance index revealed that employing the LAT system leads to 19% decreasing of fairly water deliveries along the canal. In conclusion it can be suggested that no advantageous are gained by replacing the existing Nyrpic Module Off-takes employed with the LAT system.

Since the distribution of water resources and rainfall in the country is not proportionate. Interbasin water transfer in the form of water projects for the collection, transmission and creation of appropriate quality for development of human activity is necessary. On the other hand, this type of plan according to the upstream reservoir and downstream water transfer tunnel has combination of problems hydrology (water level of the reservoir) and hydraulic (hydraulic pipe or tunnel). The hydrology and hydraulic analysis to obtain the desired conditions should be simultaneous. In this studied four dams (Yalan, Pashanedegan, Gokan and Zayanehroud) and three tunnels to transfer water from the Yalan dam to Pashandegan dam have been used. In order to simulate and optimize this project, two algorithms associated with each other and connected to EPANET dynamically for solving water resources and hydraulic model and differential evolution algorithm. Since the water in the tunnels is under pressure for the entire study for water transfer efficiency of 95 percent is defined, by increasing the height of each of the dams should reduce the tunnel diameter. The results showed that weighting factor of 0.5 and crossover constant of 0.5 and population and generation of 1000 and 1500 respectively has provided an optimal solution in DE algorithm. Optimal cost by 95% transfer efficiency is equal to 14014.5 Billion riyals.

Flow dynamics at river confluences can be characterized by six major regions of flow stagnation, flow deflection, flow separation, maximum velocity, flow recovery and distinct shear layers. The junction angle, discharge ratio channels and bed elevation differences are the parameters that affect the magnitude of these regions. Most of previous studies have paid attention to the concordance canal confluences, but few studies have been conducted on the bed discordance confluences. This study investigates the effect of junction angles on flow dynamics (separation zone, flow patterns and water level) in concordance and discordance bed levels of confluences by using a 3-D numerical model (Flow-3D). Important factors that are considered in this study are the four discharge ratios (ratio of tributary channel discharge to total discharge equal to 0.2, 0.33, 0.5 and 0.67), three angles (45, 60 and 90 degree) and variable river bed levels. The numerical simulation results showed good agreement with the experimental results. The results indicated that there are a lot of differences between dynamic of confluences with concordance and discordance bed levels and the junction angle plays an important role at the river confluences, especially in bed concordance junctions. Also as the angle increases, the flow separation zone dimensions increases; in such a way the separation zone length at 90 degree angle was 2.3 times of 45 degree in concordance bed level. Finally the value in case of relative bed discordance levels of 0.1, 0.2 and 0.33 were found to be 4.5, 3 and 2.1, respectively.

In this research, the reasons of failures in concrete linings in Shabankareh irrigation project were studied. In this context, a detailed field survey was performed and all concerning technical reports were studied. In the second stage, several test pits were dug along the canal embankment and soil samples were taken from different depths. All samples were tested for their chemical, physical and mechanical properties. The results of grain size analysis and Atterberg Limits tests showed that most samples werer coarse grained soils with classification of GP, GM, GP-GM and SM according to USCS standards. The results of Pin Hole tests showed that some samples were of medium to highly dispersive type. The results of the chemical tests indicated that the gypsum content of the soils varied from 2 to 70 percent. Based on the overall results of the field and laboratory investigations, the main causes of the damages to the lining were related to geotechnical properties of the foundation soil. Also, it was concluded that the existence of gypsum particles in the bed materials was mainly responsible for the failures. Finally it was observed that Gypsiferrous soil layers under the lining were easily dissolved and eroded by seepage flow and surface runoff and cavities were formed extensively, which in turn caused lack of support of the concrete slabs, and general failure of the lining.

Stilling basin as an efficiently hydraulic structure to dissipate the kinetic energy of supercritical flow generated at the downstream of a spillway and in some cases to get an economic design use baffle blocks, end sill is used in stilling basin. For control of and reducing the length of hydraulic jump, build a short sill in a stilling basin as a continuous sill can be effective. The present study focuses on the effects of a perforated stepped sill on the characteristics of hydraulic jump in ogee spillway stilling basin was. Experiments were performed for four ratios of opening of holes equal to 12, 25, 50 and 70% at three relative distance equal to10.4, 14.6 and 18.75. The results showed that using Perforated stepped sill in a stilling basin has a positive effect on control and would fix the position of hydraulic jump in a stilling basin, and that the sill with ratio of opening equal to 25% at relative distance equal to10.4 showed a maximum effect on reduction of the length of hydraulic jump compared to other sills and length of hydraulic jump reduction of 40.8% on an average in case of classical hydraulic jump. Also the best position for the sill with ratio of opening equal to 12%, based on reduction of the length of hydraulic jump is the relative distance more than 14.6. also decrease the ratio of opening and the relative distance have a positive effect on the relative energy dissipation, so that the sill with ratio of opening equal to 12% at relative distance of equal to10.4, increased the relative energy dissipation of 11% on an average as compared to the classical hydraulic jump.

In arid and semi-arid regions, due to shortage of permanent surface water resources the optimal use of groundwater becomes important. In this regard, the storage of sub-surface flow within alluvial reservoirs of underground dams appears to be economical, and cost-effective. In some cases, because of the lack of construction materials at the site, the cost increases. In this case a combination of available construction materials and bentonite can meet the required criteria. In this research, by constructing a physical model of underground dam the effect of adding bentonite on decreasing horizontal saturated hydraulic conductivity in non-cohesive soil was investigated. For this purpose, 2, 4 and 6% (by weight of dry soil) of bentonite was added to the soil and after compaction by using a model, hydraulic permeability was measured. The results indicated that the hydraulic conductivity decreases with increase in the bentonite content due to the high specific surface area and high swelling potential of bentonite. Also hydraulic conductivity was reduced because of steep slope (up to 4% of bentonite) and with further increase in hydraulic conductivity the reduction rate was slowed down so it can be said that the relationship between the logarithmic graph of hydraulic conductivity and the bentonite content can be represented by a linear model. Based on this model, 4.6 percent of bentonite is required to reduce the saturated hydraulic conductivity of a noncohesive soil equal to the saturated hydraulic conductivity of the soil used in the core of the Sanganeh underground dam (in a similar relative compaction).

The piano key weirs (PKWѕ) are type of nonlinear weirs which can increase the discharge for a given width without the increase in head water .In piano key the length of weir crest in both upstream and downstream can be incresead and therefore can be considered to be a suitable substitution for the labyrinth weirs, with a relatively small footprint In this study, in order to evaluate the Hydraulic performance of PKWs of free & submerged flow, totally 554 experiments are conducted on 11 physical models. Results showed that in the free flow the PK1.4 (inlet over outlet key width; wi /wo=1.4) in the head water ratio of 0.5≤Ho/P≤1 and the PK1.25 in Ho/P≥0.1 as compared with other weirs, has higher Hydraulic performance. In the case of constant values for the wi/w₀ ratio and changing of the floor slope from 1:1.5 to the curve (a quarter of the circle; PKC) the discharge coefficient of these weirs increased about 3 percent. In the condition of submerged flow the value of the submerged upstream head over the free flow of upstream head (H*/Ho) increased by decreasing the submerged upstream head ratio (Ho/P). For the PK1 weir and in the submergence values lower than 0.48, the downstream depth had no effect on upstream depth of weir, and H*=Ho. The modifying of PK1 causes a decrease the modular submergence range in this weir and occurrence of the full submergence with a little delay. Modifying of PKC1, lead to an increase in the modular submergence range and no change in the full submergence.

The subject of this study was to evaluate the water delivery and find solution for increasing water productivity in Doroodzan irrigation and drainage network. Five water delivery indices such as water delivery adequacy, water delivery efficiency, water delivery equity, water delivery dependability, and delivery performance ratio were measured. The indices were measured in 12 selected third grade tertiary canals for at two irrigation intervals during spring season. Evaluations were accomplished for two water requirement scenarios based on the primary design condition (based on hydromedol) and current condition (based on Penman Montieth evapotranspiration model and efficiencies). Statistical analysis was performed using Chi-squared test and standard and average errors. Results showed that the water delivery equity and water delivery dependability values were equal to 0.31 and 0.12, which can be categorized as poor and fair, respectively, based on the standard values. The average of water delivery performance ratio based on the primary and current condition approaches were 1.41 and 0.61, which indicates that the exess and deficit delivered water were about 41% and 39%, respectively. Water delivery efficiency index for the two approached were about 0.79 and 0.97, while the water delivery adequacy were about 0.93 and 0.56, respectively. Generally, the differences between the water delivery adequacy, water delivery efficiency and delivery performance ratio in the two studied water requirement approaches were considerable. Therefore, the approach based on Penman Montieth evapotranspiration model and efficiencies should be considered instead of hydromedol approach for water requirement assessment in Doroodzan irrigation network.

Flap gates are used to measure the flow in canal and are considered as a hydraulic engineering topic, which lacks enough attention so far. Use of flap gate as a measuring tool requires extended studies in order to be recommends as a measuring device for different types of gates. The structures could provide an acceptable economic condition in flow measurement applications where, low costs of manufacturing, installation, and operation could be achieved. This paper presents the discharge estimation from flap gates in rectangular canals under free and submerged flow conditions by using regression and analytical techniques. The derived discharge equations are resulted from the combination of energy and momentum equations. The suggested equations were validated by means of experimental observations, which showed an average error of 1.06% to 1.91% at free flow and 2.28% to 5.26% for submerged flow conditions. The paper also presents some diagrams for estimating the discharge coefficient of flap gates in both flow conditions.