مجله مهندسی و مدیریت آبخیز
سال هفتم شماره 2 (تابستان 1394)

Due to the water resources limitation in the country, subsurface flow of the seasonal rivers has an important role. These water resources can be used when collected by underground dams in locations with appropriate properties. In order to use the subsurface flow, it is necessary to estimate water resources potential accurately. Therefore, the aim of this study is to estimate the volume of subsurface flow using Salas model based on hydrologic balance. For this reason, the meteorologic and hydrometric information and data of 15 stations were by gathered and two hydrometric stations of Abgelal and Marghab were chosen as suitable ones by assessing and field survey. At these stations, the balance of subsurface flow was estimated using the above mentioned model. The results showed that in Abgelal watershed, 73 and 11 percent of the total rainfall were lost due to evapotranspiration and infiltration respectively, and just 16 percent was outflowed from watershed in the form of surface runoff. Also, most of the rainfall was outflowed through surface runoff in Marghab watershed and the coefficient of runoff was 58.7 percent. In this watershed, 41.2 percent of the total rainfall was infiltrated and 29.9 percent was lost due to evapotranspiration and 27.4 percent was infiltrated. Considering the area of Abgelal watershed of 151.6 km2, about 8.4 million m3 is drained annually as subsurface flows. According to the area of Marghab watershed of 664.3 km2, annually about 250 and 43 million m3 are drained as surface and subsurface flows, respectively. Also, evaluation of the model in both stations using relative root mean square error, Nash-Sutcliffe efficiency and mean absolute error, showed the amounts of 2.53, 0.53 and 10.08 in Marghab and 0.97, 0.32 and 8.9 in Abgelal station.

Human life is affected by different hydrological events such as floods, water storage, droughts, water pollutions, avalanche and etc. that the risk range of these events depends on the behavior of hydrological variables and watersheds characteristics. Lack of correct data and information or inadequate correct data is the important factor affects on regognition of the behavior of hydrological variables and watershed charactristics. In this regard, there are different models which could follow watershed characteristics and estimate or simulate runoff and sediment load and other water balance factors in watershed. SWAT model is one of the important hydrological models. In this research, Atrak River monthly runoff was simulated using this model based on collected data in Maraveh Tappeh watershed, Gholestan province, Iran. Required information such as topography, land use, pedologyand also, hydrological and meteorological data such as daily rainfall, temperature, relative humidity and runoff have been collected. To determine important and sensitive parameters, sensitivity analysis has been performed using one parameter at a time (OAT) method. The results indicated that curve number, channel hydraulic conductivity, surface runoff lag coefficient, base flow alpha factor and soil evaporation compensation factor have the most influence on different parts of water balance. Calibration and validation of the model were performed using the SUFI2 algorithm for the periods of 1994 to 1999 and 2000 to 2008, respectively The simulation accuracy using Nash-Sutcliffe and coefficient of determination were 0.54 and 0.54 for the calibration period and 0.46 and 0.46 during the validation period, respectively. So, it can be concluded that the performance of the SWAT model for estimating monthly flow is quite good.

Rainfall erosivity is one of the most important factors in determining soil erosion. This factor is usually expressed as erosion indices that are based on rainfall characteristics.In this study, after construction of 12 runoff-sediment plots in Nir Research Station in Yazd province, the amount of runoff and sediment from each plot were monitored and measured for 12 rainfall events. Then, based on a world wide literature review, 61 rainfall erosivity indices were identified. The rainfall erosivity indices were determined for each of the storms with extracting the required parameters. In order to determining suitable rainfall erosivity indices, the correlation between the rainfall erosivity indices and soil loss values were determined. The results showed that PI602, PI302, RPI602, RPI302, RI60 with 0.730, 0.713, 0.703, 0.694 and 0.664 percent had highest correlation with soil loss amount. Generally, in the climatic condition of study area, the indices based on rainfall intensity with total amount of rainfall multiply in the square of 60 and 30 minutes rainfall are better than other indices.

Now a day, long-term prediction of climate variables is necessary for climate change impact studies. Currently Global Circulation Models (GCM) are powerful tools to generate climate scenarios. These models are limited to capture the local climate due to their low spatial resolution. So, they cannot be directly applied for hydrological modeling in a catchment scale. In this research, first the trend of variables such as rainfall, radiation, maximum and minimum temperature were assessed for the base period with nonparametric Man-Kendall test. Second, these variables were downscaled by using the outputs of HADCM model and under three scenarios of A1, A2 and B1 which are accepted by IPCC(1971-2010) under three scenarios and their monthly changes were investigated for three periods of 2011-2030, 2046-2065 and 2080-2099 compared to the base predicted period of (1971-2010). All these scenarios showed almost similar results on precipitation shortage and increasing of solar radiation, minimum and maximum temperature over the future periods. As an example, the results of A2 scenario showed increasing of the annual mean, minimum and maximum temperature by 1.1, 3.2, and 4.6 °C, increasing of solar radiation by 0.07, 0.30 and 0.33 mJ m-2d-1 and decreasing precipitation by 16.4, 17.6 and 31.9 percent for these periods compared to the base period.

Studies of climate change and its impacts on the frequency and intensity of future droughts can help programming for the management of water resource and adaptation of the destructive effects of this phenomenon. The aim of this research is trying to assess the climate change in 2011-2030 period and its impact on drought in Eskandari Basin. To achieve this purpose, after validating Lars-WG to generate weather parameters, HadCM3 output downscaled under A2 and B1 scenarios. Next, minimum and maximum temperature and precipitation was predicted. Also, SPI index was calculated. Underlying these scenarios minimum temperature growth dramatically in March, June, July and September 0.3 to 1.6 °C. Additionally, highest and lowest increment in maximum temperature will occur about 0.02 and 1.6 in May and April, respectively. However, the results indicated an increase of 7.2 to 10.9 percent in the average of annual precipitation, but due to the fact that there is no any increase in the number of wet days, extreme rainfall intensity will soar remarkably. Substantial reduction in precipitation belongs to May and April. Regarding this issue, this shortage will affect with several months lag and the most severe agricultural drought will occur in August and hydrological drought will fall out in December based on six and 12 months SPI, respectively. Annual analysis showed that 75 percent of the years are in normal condition. Therefore, in Eskandari Basin, increasing drought frequency will not be expected in 2020s. But, precipitation oriented towards warm seasons.

In undeveloped and less developed countries of arid zones, the easiest way for water supply is withdrawal of groundwater. The negative perception of this method of water discharge is clear. Spreading floodwater is one of the water resources management strategies in arid and semi-arid zones that has positive impacts on groundwater resources. The aim of this research was to demonstrate the impact of floodwater spreading on quantity of groundwater in Gareh Bygone Plain, Fasa, Fars province, Iran. Annual changes of water level was determined by reviewing water level of monthly data (1992-2013) of four piezometric wells. Despite to the spreading floodwater, the general trend of groundwater level was declining. Thus, for demonstrating the role of the floodwater spreading in groundwater recharge, changes in groundwater levels were investigated in the years of increases and decreases of floodwater. Results showed that the least recession is in piezometric wells 1 and 3. Piezometric well 1 due to the effect of fault and piezometric well 3 due to the effect of floodwater spreading. Results of Principal Components Analysis (PCA) of monthly water level in four piezometric wells showed that the first component as the most important indicator of recession of water level in the region is more than 83% of the variance. Sorting PCA loadings on the first component, represents a high recession in piezometric wells 2 and 4 that corresponds with the results of recession map of the plain. Piezometric well 2 due to evapotranspiration of trees and piezometric well 4 due to excessive extraction of water for agriculture in the area showed the most recession.

Hydro-meteorology parameters are sensitive to climate change. Therefore, it is important to investigate the present climate change pattern and its impact on water resources. Changes in a series may occur gradually or abruptly. Both of these changes could be detected by non parametric statistical tests. In this research, mean annual discharge flow and mean annual rainfall were selected for detection trends in Karkheh Watershed, one of the mountainous watersheds in Iran, using the Wilcoxon and Spearman rank correlation tests. Result showed that, both studied variables exhibit decreasing trend in the selected stations. But, no step changes were found in the time series. The observed trend in the upper area of the watershed may adversely affect the human activities of the region.

The physiographical and climatological attributes of basins and maximum annual flood statics were obtained from 38 hydrometric stations of Mazandaran Province. The first, physiographical space based interpolation method was used for regional flood analysis with 10, 20, 50 and 100 year return periods. The Canonical Correlation Analysis was used to design physiographic space and regional analysis was obtained application of three interpolation methods include, ordinary Kriging, simple Kriging and IDW in the physiographic space. The results showed at-site flood quantiles have maximum correlation spatial in the physiographic space and their spatial structures following from Gaussian semi variogram. In order to evaluated the accuracy results using L-moments method for regional flood frequency analysis. In this method Ward clustering has been used to the determination of homogeneous regions. Homogeneity areas were adjusted by using homogenous and discordancy tests. Using goodness-of-fit Z DIST the Generalized Logistic distribution was selected for all clusters as the best regional distribution and regional estimates obtained by parameters selected distribution. Finally, performance methods evaluated using Jack Knife procedure and the five statistical indexes BIAS, BIASr, RMSE, RMSEr and NASH. Both methods give the same and desirable performance based on NASH; however results of other indexes showed that physiographical space based interpolation method provide better performance than linear moments and improving estimated by increasing the return periods, while the L-moments offers better performance for short return periods. The results of interpolation indicated that geostatistics estimates have more accuracy than deterministic estimates and ordinary Kriging has best performance.

Climatic conditions in arid and semi-arid regions, poor vegetation cover and mountainous conditions of watersheds concentrates surface water as floodwater and cause vital and financial damages in industrial, urban and rural areas. Runoff threshold is one of most important factors in accurately estimation of flood volume and intensity for designing and securing constructive projects which saves expenses and leads to optimum dimensions of structures. In this research, rainfall simulator was used to investigate the effective factors on runoff threshold. Rainfall intensities of eight to 40 mm/h in periods of 15, 30, 60 and 120 minutes were simulated and runoff thresholds were measured. Acceptable methods for estimation of runoff threshold were introduced based on rainfall characteristics and pedology and geology parameters using measured data and multivariable linear and nonlinear regression methods. Results demonstrated that the rainfall volume and intensity as climatic factors, vegetation cover and slope as terrain factors and soil texture as pedologic factors are the most effective ones in runoff threshold. The relation of independent factors and their partnership in runoff threshold is statistically acceptable for the research area. The results showed a significant correlation (R2=0.98) between estimated and viewed runoff threshold.

Optimum application of precipitation, especially snow and rain, is very important, particularly in arid and semi-arid areas. Establishing rainwater harvesting systems with high runoff coefficient and therefore runoff storage can produce sustainable conditions to meet the water requirement of the plants and trees in dry seasons. For this purpose, three treatments including natural surface intact, covered with riprap and plastic cover with riprap were selected. The areas of each experimental plot were four m2 with square shapes and average slope of 11-18 percent were constructed. Results from 34 rainfall events showed that the amount of runoff from natural surfaces with riprap, intact natural surface and plastic cover with riprap treatments were 13, 20 and 57 percent of the amount of rainfall, respectively. The rainfall thresholds to initiate runoff in the treatments were 5.3, 4.7 and 2.6 mm, respectively. The highest runoff produced by plastic surface with riprap and this system is suggested as an appropriate option to collect rainwater in this study.