Akhilesh KumarBansal, Gireesh Kumar2019-06-192019-06-192004-05http://krishikosh.egranth.ac.in/handle/1/5810109186The present study was carried out with the objective to observe the sediment outflow for variable intensity-duration storms and also for different rainfall commencement periods at selected land slopes under simulated rainfall conditions by using a rainfall simulator of size 10 m 1.4 m and a hydraulic tilting flume of size 10 m 1.2 m 0.5 m. with the locally available soil material collected from Crop Research Centre (CRC), Pantnagar. In this study, three rainfall intensities viz. 9.0 cm/h, 13.2 cm/h and 17.0 cm/h for three selected rainfall durations of 10 min, 20 min and 30 min were considered at 0 %, 2 % and 4 % land slopes in case of isolated storms. The complex storms were created by combining two and three rainfall intensities for total 30 min storm duration. The timing of occurrence of these intensities was regulated in a way such that different rainfall patterns viz. advanced (ARP), delayed (DRP), intermediate-I (IRP-I), intermediate-II (IRP-II) and uniform (URP) were obtained. Apart from the above, attempts were also made to observe and quantify the effects of time gap between two successive rainstorms called as “rainfall commencement period” over sediment outflow behaviour at different land slopes. For this purpose, an isolated storm of 13.2 cm/h rainfall intensity for 10 min duration was applied for selected rainfall commencement period of 0 h, 1 h, 3 h, 6 h and 12 h at each of the selected land slopes. The total runoff volume was observed to be almost the same for a particular rainfall input at every land slope. However, the distribution pattern of runoff was observed to be different with the change in land slope. The average sediment concentration was found to be increasing with the increase in land slope in every case but did not provide any definite trend with the rainfall intensity, duration, rainfall pattern and rainfall commencement period. The rate of sediment outflow was found to be increasing with the increase in land slope as well as in rainfall intensity but found to be decreasing with the increase in rainfall duration. However, the total sediment outflow increased with the increase in land slope, rainfall intensity and rainfall duration in case of isolated storms. In case of complex storms CS2RI and CS3RI, the sediment outflow rate and total sediment outflow did not provide any definite trend with the rainfall distribution pattern. However, in general both of them were found to be increasing with land slope under a particular rainfall distribution pattern. The sediment outflow rate as well as total sediment outflow were found to have a decreasing trend with the increase in rainfall commencement period at a particular land slope but found to be having an increasing trend with land slope for a given rainfall commencement period. Mathematical relationships were developed relating average sediment concentration and sediment outflow rate with rainfall intensity, land slope, rainfall duration and rainfall commencement period as per the case. It was observed that log transform values of average sediment concentration and sediment outflow rate had a good correlation with rainfall intensity land slope, rainfall duration and rainfall commencement period. The correlation coefficient of developed models was found to be more than 90% in generaennullThesis