Time filter

Source Type

Saghafian B.,Soil conservation and Watershed Management Research Institute | Noroozpour S.,Shahid Chamran University
Journal of Hydrology

Du et al. (2009) presented a time variant spatially distributed travel time method in order to simulate storm runoff response for a watershed in China. There are a number of issues raised in their paper that require further thoughts. One of the important issues is the assumption of travel time being dependent on the flow velocity rather than the wave celerity. Another problem deals with the introduction of a parameter (K) that accounts for the estimation error for roughness coefficient and bed slope. While the default K value must be unity, a value of 7.5 was calibrated. Other issues deals with ignoring the effect of flow accumulation in overland cells, calibration of a sensitive channel threshold parameter, trying to keep the mass conserved through the routing procedure while the isochrone locations vary in time, and the application of SCS infiltration method during the no-rain period. This commentary elaborates on the above issues. © 2009 Elsevier B.V. All rights reserved. Source

Mostafaei A.,Soil conservation and Watershed Management Research Institute | Mostafaei A.,Shahid Chamran University
Environmental Management

The Kashkan River (KR), located in the west of Iran, is a major source of water supply for residential and agricultural areas as well as livestock. The objective of this study was to assess the spatial and long temporal variations of surface water quality of the KR based on measured chemical ions. The Canadian Council of Ministers of Environment Water Quality Index (CCME WQI) technique was utilized using measurements from 10 sampling stations during a period of 36 years (1974-2009). The measured data included cations (Na+, K +, Ca2+, Mg2+), anions (HCO3 -, Cl-, SO4 2-), pH, and electrical conductivity. Principal component analysis was performed to identify which of the parameters to be included in the CCME WQI calculations were actually correlated and which ones were responsible for most of the variance observed in the water-quality data. In addition, KR water quality was evaluated for its suitability for drinking and irrigation purposes using conventional methods. Last, trend detection in the WQI time series of the KR showed water-quality degradation at all sampling stations, whereas the Jelhool sub-basin more adversely affects the quality of KR water in the watershed. Nonetheless, on average, the water quality of the KR was rated as fair. © 2014 Springer Science+Business Media. Source

Martins D.S.,University of Lisbon | Raziei T.,University of Lisbon | Raziei T.,Soil conservation and Watershed Management Research Institute | Paulo A.A.,University of Lisbon | And 2 more authors.
Natural Hazards and Earth System Science

The spatial variability of precipitation and drought are investigated for Portugal using monthly precipitation from 74 stations and minimum and maximum temperature from 27 stations, covering the common period of 1941-2006. Seasonal precipitation and the corresponding percentages in the year, as well as the precipitation concentration index (PCI), was computed for all 74 stations and then used as an input matrix for an R-mode principal component analysis to identify the precipitation patterns. The standardized precipitation index at 3 and 12 month time scales were computed for all stations, whereas the Palmer Drought Severity Index (PDSI) and the modified PDSI for Mediterranean conditions (MedPDSI) were computed for the stations with temperature data. The spatial patterns of drought over Portugal were identified by applying the S-mode principal component analysis coupled with varimax rotation to the drought indices matrices. The result revealed two distinct sub-regions in the country relative to both precipitation regimes and drought variability. The analysis of time variability of the PC scores of all drought indices allowed verifying that there is no linear trend indicating drought aggravation or decrease. In addition, the analysis shows that results for SPI-3, SPI-12, PDSI and MedPDSI are coherent among them. © 2012 Author(s). Source

Shoaei Z.,Soil conservation and Watershed Management Research Institute
Environmental Earth Sciences

Seimareh Landslide (SL) is globally recognized as one of the largest rock mass movements in the world. It is located along the border of Ilam and Lorestan provinces in southwest Iran, in the heart of the Zagros Mountain Range. There are controversial findings about the mechanism of the landslide formation. This field work study reviewed the possible mechanisms of failure and analyzed post-failure geomorphic features. Drainage pattern disturbance in the depositional region and consequent dammed lake formation are among the most significant characteristics of these features. Seimareh, Jaidar and Balmak are three large landslide-dammed lakes. The present study analyzed the processes responsible for the formation and erosion of the Jaidar and Seimareh Landslide dams using the available annual sedimentation and field measurements of the sediment deposited in these lakes. The results showed that the SL dam has been formed about 935 years after the landslide event. Detailed field investigations indicated a specific hydro-morphological condition in the landslide area. The results implied that the main causes of the failure were probably the particular hydro-morphological characteristic of the landslide source area together with the enormous eroding energy resulted from merging of two high-flow rivers which eroded the base of the southern flank of Kabir-kuh Mountain. However, the unusual size of the landslide suggests that an external factor, e.g., a huge earthquake, might have triggered the failure. © 2014, Springer-Verlag Berlin Heidelberg. Source

Raziei T.,Soil conservation and Watershed Management Research Institute | Bordi I.,University of Rome La Sapienza | Pereira L.S.,University of Lisbon
Water Resources Management

The lack of reliable and updated precipitation datasets is the most important limitation that hinders establishing a drought monitoring and early warning system in Iran. To overcome this obstacle, we have evaluated the applicability of GPCC and NCEP/NCAR precipitation datasets for drought analysis in Iran. For this purpose, drought variability across the country has been analyzed through the standardized precipitation index (SPI) on 12-month time scale based on the common period 1951-2005. For each dataset, by applying the principal component analysis (PCA) to the SPI field and Varimax rotation, the studied area has been regionalized into a few distinctive sub-regions characterized by independent climatic variability. Results have been checked against observations at 32 rain gauge stations having reliable data for the study period. Both GPCC and NCEP/NCAR datasets identify the same sub-regions of drought variability and they are in good agreement with observations. However, the NCEP rotated principal component scores associated with the sub-regions show different time variability with respect to the behaviours captured by GPCC, on one hand, and observations, on the other hand. It seems that, in central Iran such differences concern mainly the period before the seventies. Thus, the results suggest that GPCC dataset is a useful tool for drought monitoring in Iran and it can be used to complement the information provided by rain gauge observations. The NCEP/NCAR reanalysis dataset shows a better agreement with observations for the period 1970-2005 than for 1951-2005, and its discrepancies in the regional time variability of drought with respect to GPCC and observations should be taken into account when periods before the seventies are considered. © 2010 Springer Science+Business Media B.V. Source

Discover hidden collaborations