Generation[ edit ] Surface runoff from a hillside after soil is saturated Surface runoff can be generated either by rainfall, snowfall or by the melting of snow, or glaciers. Snow and glacier melt occur only in areas cold enough for these to form permanently. Typically snowmelt will peak in the spring and glacier melt in the summer, leading to pronounced flow maxima in rivers affected by them.
The yellow lines represent flows computed by the surface runoff modules.
Hortonian surface runoff, soil infiltration, impervious storage processes, and optionally cascading Hortonian flow and surface-depression storage processes. The cascading flow and surface-depression storage options are described in other training videos. Hortonian surface runoff computed from impervious, pervious, and surface depression fractions can flow directly to the stream network and cascade from HRU to HRU.
The dashed lines are internal fluxes and the solid lines are fluxes leaving or flowing Surface runoff an HRU. Precipitation, air temperature, and solar radiation drive the storage and exchange of water in and from each water-storage reservoir.
The primary reservoirs are the plant canopy, snow pack, impervious surfaces, surface-depressions, soil zone, and groundwater storage. Surface-depression storage is not shown. It is similar in conceptualization to impervious surfaces in that it occupies a fraction of the HRU land-surface area and has a specified maximum water-holding capacity.
The pervious fraction of the HRU area is 1. Inflows to the surface-runoff modules are rain throughfall as computed in the interception module, snowmelt as computed in the snow module, and potential ET as computed by the selected potential ET module.
Optional inflows to HRUs as computed in the surface-runoff modules are cascading Hortonian surface runoff and capture of a specified fraction of Hortonian surface runoff in surface depressions.
Outflows are Hortonian surface runoff from the pervious and impervious fractions, soil infiltration to the pervious fraction, evaporation from the impervious and surface-depression fractions, and spillage, interflow, and seepage from the surface-depression fraction.
The surface-runoff modules have no computations for inactive and lake HRUs. All processes are computed for land HRUs. Lateral flows are not computed for swale HRUs, thus computations related to Hortonian runoff, except for surface-depression runoff capture within an HRU, are not computed while all other land HRU processes are computed.
The remaining fraction is attributed to ET, 40 percent for the natural area and 30 percent for the urban area. Urban areas can produce significant storm-water flows, as much of the runoff is routed directly to the stream network.
In this example, the urban area has 45 percent more runoff and 35 percent less infiltration than the natural area. To mitigate the impact of impervious surfaces in new urban and suburban development, detention ponds are constructed to reduce surface runoff and increase infiltration.
The baseline condition is percent forested. As development increases peak storm-water discharge increases. However, the increase in storm-water flow may be non-linear.
Part of the non-linearity is related to reduced soil infiltration and plant transpiration as development increases. Users could develop simulations using different values of impervious fractions to estimate changes in storm-water flow. The top two graphs are conceptualizations of infiltration excess, which is termed Hortonian runoff.
The first represents storm-water flowing across the entire land surface with some infiltration, such as over soil with low permeability.
Computation of Hortonian runoff from impervious areas is based on this conceptualization. The second graph illustrates storm water infiltrating upslope with some water infiltrating and some flowing as Hortonian runoff near the bottom of the hillslope. This is a partial contributing-area process and is used to compute Hortonian runoff on pervious areas.
The third graph illustrates saturation excess or Dunnian Runoff, where upslope storm water infiltrates and near the bottom of the hillslope water is discharging to the land surface. The fourth curve illustrates subsurface stormflow where water infiltrates to areas where the water can flow quickly through high conductivity features, such as animal burrows, root channels, leaf litter, gravel layers, etc.
This type of flow is termed preferential flow in PRMS. The fifth curve illustrates water that has infiltrated the soil and moves laterally downslope based on soil characteristics and gravity. This type of flow is termed interflow in PRMS. Dunnian, preferential flow and interflow are computed in the Soil Zone module that is described in another training video.
The yellow areas are where the soils are below their water-holding capacities. As soil saturation expands during a storm, the contributing areas expand.
As the soils dry as a result of ET, recharge, and lateral flows, the contributing areas recede. A portion of snowmelt can be specified to be the first component of infiltration, thus not available for computation of Hortonian runoff.Water erosion is a mechanical process involving the energy from the impact of raindrops on soil surface, directly associated with rainfall kinetic energy and the shear stress corresponding to the surface runoff itself (Panachuki et al.
Surface runoff (also known as overland flow) is the flow of water that occurs when excess stormwater, meltwater, or other sources flows over the Earth's lausannecongress2018.com might occur because soil is saturated to full capacity, because rain arrives more quickly than soil can absorb it, or because impervious areas (roofs and pavement) send their runoff to surrounding soil that cannot absorb all of it.
Surface runoff is a major component of the water cycle. It is the primary agent in soil erosion by water. Runoff that occurs on the ground surface before reaching a channel is also called a nonpoint source.
Runoff (surface water runoff) When rain or snow falls onto the earth, it just doesn't sit there, it starts moving according to the laws of gravity. Surface runoff is precipitation runoff over the landscape In our section about water storage in the oceans we describe how the oceans act as a large storehouse of water that evaporates to become .
surface runoff[′sər·fəs ′rən‚ȯf] (hydrology) Runoff that moves over the soil surface to the nearest surface stream. Surface runoff The precipitation, snow melt, or irrigation water in excess of what can infiltrate the soil surface and be stored in small surface depressions; a major transporter of non-point-source pollutants in rivers, streams.