Shiraz University Iranian Journal of Science and Technology Transactions of Civil Engineering 2228-6160 29 3 2013 01 25 Estimating storm erosion index in southern region of I. R. Iran 357 363 789 10.22099/ijstc.2013.789 EN Journal Article 2013 01 25 A universal soil loss equation is used for predicting soil erosion. Rainfall erosivity (EI) in this equation is related to storm type, amount, and intensity, so it should be calculated from rainfall characteristics. In the present research, data of 13 recording rain gauge stations at the southern region of the Islamic Republic (I.R.) of Iran were analyzed and single storm, daily, monthly and annual erosion indices (MJ.mm.ha^-1.h^-1) were calculated and estimated by different simple models. For a single storm erosion index, the model EI=a P_e^b/D^gwas modified. A coefficient of a  for stations without snowfall and with an elevation of less than 1000 m, or higher than 1000 m, and b for stations without snowfall were 0.51, 0.21 and 2.0, respectively. The values of a and β for stations with snowfall and g for both types of stations may be determined based on the station elevation using the proposed equations. For a daily erosion index, a power function (EI=ahb) was derived (h is daily rainfall, mm). The value of a was dependent on station conditions, but an average value of 1.61 was obtained for b. For monthly erosion index, a simple model was proposed as  <span style="font-size: x-small;">where H is the elevation (m), and P_m24 is monthly,  maximum  daily rainfall  (mm).  The coefficients of the Arnoldus model were modified for the study region to estimate the annual erosion index using annual maximum daily rainfall (P_a24, mm), monthly (P_i, mm) and annual rainfalls (P, mm) as follows:  </span> <span style="font-size: x-small;">                             </span> <span style="font-size: x-small;">Using simple available rainfall data for 65 weather stations throughout the study region, the annual erosion indices were calculated by the above equation and an iso-erosivity map for the study region was prepared.           </span>  

Shiraz University Iranian Journal of Science and Technology Transactions of Civil Engineering 2228-6160 29 3 2005 06 25 The initiation of sediment motion in fixed bed channels 365 372 790 10.22099/ijstc.2005.790 EN Journal Article 2003 07 01 The transport of sediment in open channels is a complex process, and the physics of this phenomenon have not been completely explored. The majority of research work on sediment transport has been concentrated on beds formed of the same mobile sediment and only a few researchers have been concerned with sediment motion over fixed bed. This paper reviews the state of the problem and focuses on some practical points. Sediment threshold experiments were conducted in the two types of V-shaped bottom channels. Sand and gravel particle movements were considered and the relationship between flow discharge and bed shear stress, as well as channel bed slope were found at the threshold condition. Some practical and design equations were found to be more appropriate. It may be found that the effect of cross sectional shape on sediment threshold in fixed bed channels should be examined https://ijstc.shirazu.ac.ir/article_790_47faba0c99ddd944772390e5549cf31c.pdf