Infiltration capacity

Surface runoff. Hydrologists have identified two processes for generating surface runoff over land. The first, saturated overland flow (SOF), is generated when precipitation (or snowmelt) occurs over a saturated soil since water has nowhere to infiltrate, it then runs off over land. SOF typically occurs only in humid environments or where the water table rises to intersect with a stream. Horton overland flow (HOF or infiltration-limited overland flow) occurs when precipitation intensity exceeds the infiltration capacity of the soil in a non-saturated environment. In this case, only the excess precipitation (that exceeding the infiltration capacity) runs off over the surface. Both types of overland runoff generate relatively rapid flows that constitute the surface water contribution to the hydrograph (Fig. 6-6). 

Fig. 8-7 Three principal ratios control the style of runoff generation prevalent in a landscape (1) ratio of rainfall intensity to the infiltration capacity of the soil (2) ratio of bedrock conductivity to soil conductivity and (3) the topographic index defined by the ratio of the upslope drainage area to the ground slope. HOF = Horton overland flow SOF = saturation overland flow SSS = subsurface stormflow GWR = groundwater flow.

There was a discrepancy between water salinity limits for the three locations, which may be attributed to factors related to difference in soil texture and stmcture. This affects soil infiltration capacity and water retention. These soil hydrologic characteristics influence salt development in the soil profile, which affects plant... 

Overland Runoff The fraction of rainfall or irrigation water that flows over a land surface from higher to lower elevations, known as overland runoff, is an additional pathway for contaminant transport. Runoff occurs when the amount of rain or irrigation water is greater than the soil infiltration capacity. The formation of a crust on the soil surface is a major contributor to runoff formation in arid and semiarid zones, because it decreases the infiltration capacity. The soil crust is a thin layer (0-3 mm) with a high density, fine porosity, and low hydraulic conductivity compared to the underlying soil. This skin forms as a result of falling raindrops or sodification of soil clays. 

Horton K.E. (1937). Determination of infiltration capacity for larger drainage basins. Transactions American Geophysical Union, 18, 371-385. 

Figure 3.3 Relationship between infiltration capacity (cm h 1) and time (h) this illustrates how capacity decreases over time and will eventually reach an equilibrium value. The infiltration capacity curve can be described using the following equation /p — fc + (fo /c)e-fa, where /p = infiltration capacity (or rate) at time t (m s 1) fc = equilibrium infiltration capacity (or rate) (m s 1) /0 = initial infiltration capacity (or rate) (m s 1) k = constant representing the rate of decreased infiltration capacity (1/s) and t = time from the beginning of infiltration (s). (Modified from Fetter, 2001.)...

According to Fetter (1988), the following three scenarios can be used to describe the relationship between precipitation and infiltration rates (1) when the total precipitation rate is lower than the equilibrium infiltration capacity all of the precipitation reaching the land surface should infiltrate (2) when the precipitation rate is higher than the equilibrium capacity and less than the initial infiltration capacity (at the start of the precipitation event) all of the precipitation will infiltrate initially and (3) when the precipitation rate is greater than the initial infiltration capacity there is an immediate accumulation of water on land. In general, when the precipitation rate exceeds infiltration capacity, overland flow of water occurs, commonly referred to as Horton overland flow (HOF) (Horton, 1933, 1940). 

Rainfall that reaches the land surface can infiltrate permeable soils, with each soil having a different, but limited, capacity to absorb water. The infiltration capacity (or rate) will vary, depending on the soils current moisture content. 

When precipitation rate exceeds infiltration capacity, overland flow of water occurs, commonly referred to as Horton overland flow. 

Infiltration capacity (or rate) a soil characteristic determining or describing the maximum rate at which water can enter the soil under specified conditions, including the presence of excess water it has the dimensions of velocity (i.e., cm3 cm-2 s-1 = cm s 1). 

Horton, R.E. (1940) An approach toward a physical interpretation of infiltration capacity. Soil Sci. Soc. Am. 4, 399-417. 

Tig.17.1. Infiltration capacity in surface inches in Clarion loam as affected by manure. (From Smith et al., 1937.)... 

As shown in Table 3.24, K values declined with the decrease in grain size, which might be explained by the fact that the infiltration capacity of O2 in... 

The rainwater is divided into infiltration, surface runoff and evaporation at the boundary layer surface. Preferably, the bound layers should be impervious and redirect rainwater as surface runoff so that infiltration into the pavement is minimized. However, due to deformities the boundary layers may be an important pathway for water entering the unbound layers. The infiltration capacity depends on the permeability of the pavement and underlying construction layers and presence of cracks and other local deformities of the pavement [13]. If no deformities are present the infiltration capacity for asphalt is typically in the... 

Lets suppose that a certain location implies a high traffic load on the boundary layers. At a certain point in time, cracks may develop in the boimdary layers due to fatigue. The cracks increase the annual infiltration into the road body. The annual amount of rain and its distribution over the year is a local or regional feature. As the water content in the unbound layers increases, some of the bearing capacity is lost, which may cause settlement in the imboimd layers. A differential settlement is likely to give rise to further damage to the boimdary layer that, in turn, will increase the infiltration capacity and increase the water content and flux in the unbound layers. 

Wu, Z.Y, Lu, G.H., Wen, L. et al. 2007. Thirty-five year (1970-2005) simulation of daily soil moisture using the variable infiltration capacity model over China. Atmosphere-Ocean 45(1) 37-45. 

Undertake measures to improve microsite water availability and nutrient cycling (reduce runoff, improve soil infiltration capacity by pitting, ripping, terracing, establishing microcatchments). 

When rainfall intensity does not exceed the soil infiltration capacity, soil moisture constantly... 

Long-term land uses can also increase erosion potential if rainfall or snowmelt is not adequately accommodated on the site. In a similar manner to road systems, the impermeable surfeces created by roofs, driveways, parking areas, and walkways means that overland flow is increased and the infiltrative capacity of the site is reduced. Increased off-site erosion can result if excess overland flow is discharged to adjacent properties or the road system. 

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