Combined Effect Of Rainfall Research Articles

Water erosion processes and dynamic changes of sediment size distribution under the combined effects of rainfall and overland flow

Water erosion is a time-varying processes controlled by both rainfall and overland flow. A better understanding of dynamic changes in the sediment load and size distribution with various erosive forces can help to develop and verify erosion models. Here, a total of 11 laboratory simulation experiments were conducted in a 1 m by 3 m flume with 3 storm rainfall intensities (60, 90, 120 mm h−1) and 2 inflow rates (5, 7.5 L min−1) on a silty clay red soil. Time-series measurements of the quantity and size distribution of eroded materials were made during 50 min rainfall/inflow time. The mean weight diameter of the effective sediment, sediment enrichment ratio, average stream power and rainfall power were measured and calculated. Fine sediment particles were associated with the short-lived initial stage, which was combined with sheet flow erosion and splash erosion, whereas coarse particles were associated with the rill development and rill stable stages, which were dominated by rill erosion and interrill erosion, respectively. The <0.05 mm aggregates were transported preferentially by the suspension/saltation mechanism, while 0.105–0.25 mm aggregates resisted transportation. Additionally, the sediment load rate showed a significant linear correlation with the stream power at the sheet flow (R2 = 0.84, p < 0.01) and rill development (R2 = 0.72, p < 0.01) stages as well as the rainfall power at the rill development (R2 = 0.76, p < 0.01) and rill stable stages (R2 = 0.78, p < 0.01). Sediment size increased with increasing stream power (p < 0.05) and rainfall power (p < 0.05) only at the rill development stage. The erosion processes play a major role in particle selection, and the erosion forms, aggregate breakdown and soil surface structure development should be considered for a more accurate prediction of size selectivity and the related sediment quality.

Water and Sediment Microbial Quality of Mountain and Agricultural Streams.

Increased public health risk caused by pathogen contamination in streams is a serious issue, and mitigating the risk requires improvement in existing microbial monitoring of streams. To improve understanding of microbial contamination in streams, we monitored in stream water columns and streambed sediment. Two distinct streams and their subwatersheds were studied: (i) a mountain stream (Merced River, California), which represents pristine and wild conditions, and (ii) an agricultural stream (Squaw Creek, Iowa), which represents an agricultural setting (i.e., crop, manure application, cattle access). Stream water column and sediment samples were collected in multiple locations in the Merced River and Squaw Creek watersheds. Compared with the mountain stream, water column concentrations in the agricultural stream were considerably higher. In both mountain and agricultural streams, concentrations in bed sediment were higher than the water column, and principal component analysis indicates that land use affected water column levels significantly ( < 0.05). The cluster analysis showed grouping of subwatersheds for each basin, indicating unique land use features of each watershed. In general, water column levels in the mountain stream were lower than the USEPA's existing water quality criteria for bacteria. However, the levels in the agricultural stream exceeded the USEPA's microbial water quality criteria by several fold, which substantiated that increased agricultural activities, use of animal waste as fertilizers, and combined effect of rainfall and temperature may act as potential determining factors behind the elevated levels in agriculture streams.

Combined effects of simulated rainfall and overland flow on sediment and solute transport in hillslope erosion

Soil water erosion and nutrient transport, which are strongly affected by rainfall intensity and inflow rate, often lead to severe land degradation and unexpected water eutrophication. However, little research has been conducted on the combined effects of rainfall and runoff on soil erosion. This study investigated soil erosion and solute transport in runoff under the simultaneous influence of rainfall and runoff and evaluated the relationship between soil erosion and hydraulic parameters. The rainfall simulation and inflow experiments were conducted on a slope of 10° under inflow (10, 15, and 20 L min−1) alone and combination of inflow and rainfall (60, 90, and 120 mm h−1). Flow velocity (V), Reynolds number (Re), Froude number (Fr), stream power (ω), shear stress (τ), Darcy–Weisbach friction (f), and the ratio of the Manning roughness coefficient to average flow depth (n/h) were also measured. Both rainfall intensity and inflow rate played important roles in runoff generation, soil loss, and solute transport in surface runoff. Increasing inflow rate substantially increased runoff rate and sediment concentration in runoff either with or without rainfall impact. The combination of rainfall splash and water scouring increased runoff transport, whereas did not causally increase sediment transport. Notably, the sediment concentration or cumulative sediment load under 20 L min−1 inflow rate alone was higher than those of combinations of rainfall and inflow. Most flow belonged to turbulent and supercritical flow regimes. Solute transport in runoff was also affected by both rainfall intensity and inflow rate, and bromide concentration in runoff decreased as a power function of duration on the red soil slope. Both the Reynolds number and the average flow velocity were good indicators of unit sediment load and solute transport in runoff. In a multiple regression model, the Reynolds number was found to be the best predictor of unit sediment load with an exponential relationship. Of the studied hydraulic parameters, average flow velocity was found a better parameter than the Reynolds number when estimating solute transport in runoff under combination of rainfall and inflow.

Numerical study of the effect of soil–atmosphere interaction on the stability and serviceability of cut slopes in London clay

The stability of cut slopes is greatly influenced by seasonal pore-water pressure variations under the combined effect of rainfall and vegetation. However, predicting soil–atmosphere interaction is not straightforward, due to the complexity of both the boundary conditions involved and the hydromechanical behaviour of soils, which is coupled and highly nonlinear, rendering the use of numerical tools, such as finite element analysis, necessary. This paper discusses the numerical modelling of soil–atmosphere interaction and presents the analysis of a slope cut in London clay in a highly vegetated area. The whole life cycle of the slope is considered with phases of low and high water demand vegetation and vegetation clearance. The analysis results indicate that dense vegetation is associated with high factors of safety, but may induce large differential displacements, which are likely to affect the serviceability of the slope. Vegetation clearance, however, may initiate instability, highlighting the need for effective vegetation management to achieve a balance between serviceability and ultimate limit states. Although the case considered is representative of southeast England, it introduces the necessary tools for realistic numerical analysis of soil–atmosphere interaction.

An OGCM study of the impact of rain and river water forcing on the Bay of Bengal

AbstractIndividual and combined effects of rainfall and river discharge on the Bay of Bengal (BoB) is investigated using an Ocean General Circulation Model. A set of four sensitivity experiments, forced with same air‐sea heat flux, but retaining either river runoff or rainfall or both is carried out. These experiments show that the river water is exported out of the bay along the western boundary during winter and rain water along the eastern boundary during summer. Runoff leads to a large (&gt;3 psu) decrease in salinity in the northern bay during summer and along the western boundary during winter, with a weaker contribution from rainfall. The sea surface temperature response to freshwater forcing shows large spatial variations with eastern bay showing higher differences. The northwestern bay warms by ∼1.5°C in the presence of freshwater during summer, due to greater heat absorption within a shallow mixed layer (ML). This warming is caused in nearly equal proportions by rain and river water in early summer, but the contribution by river water dominates during peak and withdrawal phases of the summer monsoon. Northeastern bay, in contrast, is cooler by 1.5–3°C in the presence of freshwater, caused primarily by river runoff, owing to the winter cooling over a thin ML. Temperature inversions form due to surface cooling of a river stratified layer during winter in the northwestern bay and due to radiation penetrating below the ML during summer in the northeastern bay.

Parameter inversion and deformation mechanism of Sanmendong landslide in the Three Gorges Reservoir region under the combined effect of reservoir water level fluctuation and rainfall

Previous studies suggested that the Qianjiangping landslide was caused by the combined effect of rainfall and reservoir water after the first water storage of the Three Gorges Reservoir. The Sanmendong landslide with a length of 830m, an area of 2.49×105m2, an average thickness of 22m and a volume of 5.48×105m3, which is located by the Qinggan river, a tributary of the Yangtze River, is only 4km away from another famous landslide along the same river: the Qianjiangping landslide. Based on the experimental data of mechanical parameters of the landslide and displacement monitoring, a nonlinear mapping relationship between mechanical parameters of the failure mass and the displacement of landslide were established by using genetic algorithms by means of uniform design, numerical calculation and artificial neural networks. The mechanical parameters of the failure mass are obtained by the global minimization of the deviation between the calculated displacements and the monitored displacements. On this basis, the deformation mechanism of the Sanmendong landslide under the combined effect of rainfall and reservoir water level fluctuations was analyzed in detail. The results indicated that the increase of displacement of Sanmendong landslide can be primarily attributed to the combined result of reservoir water level fluctuation and rainfall.

Impact of weather parameters on cotton productivity at Surat (Gujarat), India

Global warming is casting its shadow in the form of climatic changes that is affecting the local weather conditions which has its bearing on crop production and water availability, the basic necessities for survival of life on the planet. In the present study, an attempt was made to investigate the cause of poor production of cotton in 2011-12 in Surat, Gujarat as compared to 2012-13 and 2013-14. Weather data since 2000 was analyzed and compared with the data of 2011-12 and comparison was made to find the abnormality in cotton crop productivity. It was found that during 2011-12, there was delayed monsoon, as well as during squaring and flowering stage (i.e. in August 2011) there was high rainfall (595.6 mm), maximum and minimum temperatures were above normal, during development (June-August) and flowering stage of crop (October-December) which disturbed the crop physiology indirectly affecting the yield of cotton. The combined effect of rainfall and temperature was on relative humidity that created conducive atmosphere for insect and pest attacks on crops. Due to changes in temperature and relative humidity, evaporative water demands would have further aggravated the watering needs of crop. The study concludes that erratic monsoon or delayed monsoon hampers crop physiology ultimately yield due to erratic weather conditions. Further, such changes in cotton growing areas could form the basis of planning and decisions on pricing, crop insurance, export and import policies of cotton crop.

An improved ET control method to determine the water-saving potential for farmland in Baiyangdian Watershed, China

Resource-based water-saving potential has been recognized as the reduction of evapotranspiration and water loss of inefficient irrigation systems. In this paper, an improved evapotranspiration control model is applied to calculate resource-based water-saving potential, considering the influences of effective rainfall (uncontrolled evapotranspiration) and irrigated water (controlled evapotranspiration). Farmland in Baiyangdian Watershed, a highly productive area in northern China, is analyzed to determine the water-saving potential of irrigation processes. The water-saving potential was zero, 163.90 × 106 m3, and 318.24 × 106 m3 in wet, normal, and dry years, respectively, and was greater in years with less rainfall. Under the combined effect of rainfall, crop water consumption, and crop water requirements, the water-saving potential showed obvious temporal and spatial variations. July and August comprised almost 98.6% of the annual potential. In the northeast and southwest corner of the study area, potential approached zero. The potential was 1.53 times greater in the north-central than in the south-central area. The model can furnish the appropriate timing and region to water managers for implementing water-saving strategies.

Where are all the Hepatic Mat liverworts in Scotland?

Summary The Northern Hepatic Mat is a community of liverworts which have an Atlantic distribution in Europe. Eleven of these are Northern Atlantic species, confined to the north and west of Britain and Ireland and rare elsewhere in the world. The number of these liverworts recorded in 10 km squares in Scotland can be predicted from the combined effects of rainfall, temperature, humidity and topography, which account for 43% of the variance. Several 10 km squares in Scotland which are apparently suitable for many of the 11 species have fewer records than the model predicts. It is likely that some of these are under-recorded and would be worth further bryological exploration.

Recorders of reef environment histories: stable isotopes in corals, giant clams, and calcareous algae

Time-series δ18O and δ13C records from cohabiting massive coralPorites australiensis and giant clamTridacna gigas from the Great Barrier Reed of Australia, and from calcareous green algae in a core through modernHalimeda bioherm accreting in the eastern Java Sea, provide insights into the complex links between environmental factors and stable isotopes imprinted in these reef skeletal materials. The aragonitic coral and giant clam offer 20 years and 15 years of growth history, respectively. The giant clam yields mean δ18O and δ13C values of-0.5±0.5‰ and 2.2±0.2‰ (n=67), which agree well with the predicted equilibrium values. The coral yields mean δ18O and δ13C values of-5.6±0.5‰ and-1.8±0.7‰ (n=84), offering a striking example of kinetic and metabolic fractionation effects. Although both the coral and giant clam harbor symbionts and were exposed to a uniform ambient environment during their growth histories, their distinct isotopic compositions demonstrate dissimilar calcification pathways. The δ18O records contain periodicities corresponding to the alternating annual density bands revealed by X-radiography and optical transmitted light. Attenuation of the δ18O seasonal amplitudes occurring in the giant clam record 8 years after skeletal growth commenced is attributed to a changeover from fast to slow growth rates. Extreme seasonal δ18O amplitudes of up to 2.2‰ discerned in both the coral and giant clam records exceed the equivalent seasonal temperature contrast in the reef environment, and are caused by the combined effect of rainfall and evaporation during the monsoon and dry seasons, respectively. Thus in addition of being useful temperature recorders, reef skeletal material of sufficient longevity, such asPorites andTridacna, may also indicate rainfall variations. Changing growth rates, determined from the annual growth bands, may exert a primary control on the coral δ13C record which shows a remarkable negative shift of 1.7‰ over its growth history, by comparison with only 0.15‰ negative shift in the contemporaneous giant clam record. Use of coral δ13C records as proxies of fossil fuel CO2 uptake by the ocean must be regarded with caution. The δ18O and δ13C records fromHalimeda are remarkably uniform over 1000 years of bioherm accretion history (δ18O=-1.7±0.2‰; δ13C=3.9±0.1‰,n=28), in spite of variable Mg-calcite cements present in the utricles. Most of the cement infilling is probably syndepositional, and both theHalimeda aragonite and the Mg-calcite cements containign 12.3 mole % MgCO3 are deposited in isotopic equilibrium. Therefore, in favorable circumstances these algal skeletal remains may act as the shallow water analogs of benthic foraminifera in deep sea sediments in recording ambient sea water isotopic composition and temperature.

Investigations of pipe-borne pollution in Benin City, Nigeria

Two important environmental parameters could be identified as being the main causes of pipe borne water contamination in the City of Benin. These are the combined effects of rainfall and excessive construction work and, secondly, the lack or inadequacy of plumbing codes. To study the combined effects of rainfall and excessive construction on the contamination of water, samples were tested for total coliform using the multiple-tube fermentation test. Sites were chosen to allow for the comparison of the coliform counts in areas of comparatively insignificant construction to areas of excessive public construction. Results show that in the areas of heavy public construction, the curves for both the rainfall and the coliform counts in the consumer lines were skewed in the same manner. The peak rainfall was in September (437.I mm) which corresponds to peak coliform number in the consumer lines for both Zone A (62 coliforms/100 ml) and Zone B (60 coliforms/100 ml) for the same month. When compared to the area of insignificant public construction as shown in Zone C, rainfall had little or no effect on the coliform counts either at the pumping station or in the consumer line. The maximum number of coliforms recorded for the consumer line was 5/100 ml during the month of June. Results suggest that the high counts of coliforms in the Benin City water supply could be attributed primarily to the effects of construction which resulted in pipe breakage. During heavy rainfall and flooding, water under flood pressure enters the pipes through cracks, improperly tightened joints and damaged pipes. The improper enforcement of plumbing codes or lack of such codes was also identified as another cause of the water contamination as shown in Zone D. A study of the effects of water pipes passing through septic tank drain fields also shows that such effluents served as another source of major contamination. The highest recorded number for coliforms for the pipe-borne water just before entering the septic tank drain field was 12/100 ml and after it passed through the field the number had gone up to 60/100 ml. Artificial contamination of the septic tank effluents to try to detect leaks in the water pipes passing through the absorption field was investigated. The bacterial contaminant could be recovered in the pipe-borne water and the quantity was skewed in the same manner as total rainfall between periods of sampling.

Some factors that influence egg hatch of Aedes aegypti (Diptera: Culicidae).

To determine the effects of drying, flooding, and water temperatures on egg hatch of the yellow-fever mosquito, Aedes aegypti (L.), eggs on roughened aluminum paddles were placed daily for 169 days just above the water level in glass containers in the sun and shade, and daily larval counts were made. By daily measurement of the water level in a standard container, the “hatch indicator,” the combined effects of rainfall and evaporation were determined, and these measurements provided an estimate of the production of A. aegypti from discarded open-topped containers in the field.