Effects of simulated submerged and rigid vegetation and grain roughness on hydraulic resistance to simulated overland flow

Better understanding of the role of vegetation and soil on hydraulic resistance of overland flow requires quantitative partition of their interaction. In this paper, a total of 144 hydraulic flume experiments were carried out to investigate the hydraulic characteristics of overland flow. Results show that hydraulic resistance is negatively correlated with Reynolds number on non-simulated vegetated slopes, while positively on vegetated slopes. The law of composite resistance agrees with the dominant resistance, depending on simulated vegetation stem,surface roughness, and discharge. Surface roughness has greater influence on overland flow resistance than vegetation stem when unit discharge is lower than the low-limited critical discharge, while vegetation has a more obvious influence when unit discharge is higher than the upper-limited critical discharge. Combined effects of simulated vegetation and surface roughness are unequal to the sum of the individual effects through t-test, implying the limitation of using linear superposition principle in calculating overland flow resistances under combined effect of roughness elements.

Potential of roots and shoots of Napier grass for arresting soil erosion and runoff of mollisols soils of Himalayas

In this study, a soil filled Hydraulic Tilting Flume (HTF) was used as a test plot under simulated rainfallconditions. This flume was flled with mollisols soils (sandy loam in texture) collected from tarai regionof Himalayas. The effects of root and shoot characteristics of Napier grass in terms of leaf area index (LAI),shoot length (SL), number of leaves (NL), number of tillers (NT), shoot biomass (SB), root density (RD),root length (RL), root biomass (RB), and total biomass (TB) were investigated on runoff and sedimentoutflow at 90, 120 and 150 days after planting (DAP). Four simulated rainfall intensities namely 4.0, 6.5,8.3 and 9.4 cm/h over three land slopes of 1, 2 and 3% were selected. Runoff samples collected fromwhole plant plot and only root plot were analyzed for runoff and sediment outflow. Findings revealedthat Napier grasses were very effective to reduce runoff and sediment outflow and its efficacy increasedwith the extended growth stages. The reduction in runoff and sediment outflow at 90, 120 and 150 DAPwas obtained as 56% and 85%, 68% and 90%, and 74% and 96%, respectively, as compared to bare plotconditions. It was observed that the comparative contribution of shoots in runoff rate reduction washigher than the roots. On the contrary, the root part of the plant showed more contribution in sedimentrate reduction as compared to the shoot part. Step wise regression was attempted for the selection ofeffective input parameters to establish authentic runoff and sediment outflow models. Power form ofmultiple non-linear regression (MNLR) showed very satisfactory results for predicting runoff and sedimentoutflow with coefficient of determination (R^(2)) as 97.4% and 99.0%, respectively, root mean squareerror (RMSE) as 38.8 cc/m^(2)/min and 0.126 g/m^(2)/min, respectively, and coefficient of efficiency (CE) as93.9% and 96.7%, respectively, during testing period.