Soil and Water Conservation Flashcards
needed in estimating runoff, planning erosion control measures, planning for irrigation and drainage, and water conservation in low rainfall regions
Precipitation
needed in designing structures and channels that will handle natural flows of water
Runoff
required in planning irrigation and drainage systems, moisture conservation practices, etc.
Infiltration, Evaporation and transpiration
caused by the rising of warmer, lighter air in colder, denser surroundings.
Convective Precipitation
results from mechanical lifting of the air mass over mountain barriers.
Orographic Precipitation
air is lifted through horizontal convergence of the inflow into a low pressure area
Non-frontal
associated with the movement of air masses from high-pressure to low-pressure regions.
Cyclonic Precipitation
lifting of warm air over cold air at the contact zone between air masses having different characteristics
Frontal
this involves the averaging arithmetically all the rainfall depths measured by the rain gages within the area.
Arithmetic mean
– location of the rain gauges are plotted on the map of the area and stations are connected by straight lines. Perpendicular bisectors are constructed on each of the connecting lines thereby forming polygons enclosing each rain gage. The average rainfall over the area is then estimated as the area weighted average for all polygons
Thiessen polygon
station locations and amounts of rainfall are plotted on a suitable map, and contours of equal precipitation (isohyets) are then drawn. The equation used is similar to that of Thiessen method except that the area, Ai, is the area under one isohyet, Pi.
Isohyetal
computer aided method wherein it averages estimated precipitation at all points of a superimposed grid.
Grid-Point Method
for rolling areas and non-uniform distribution of gages, distance factor fixed by location of gages is used for analysis using this method. It operates under the principle that the value of points close together in space are more likely to be similar than with points farther apart.
Inverse Distance Ratio Method
the number of years during which one storm of a given duration and intensity is expected to occur.
frequency or recurrence interval
one in which a definite law of certainty exists
Deterministic Process
governed by chance; time series INDEPENDENT
Probabilistic Process
governed by chance; time series DEPENDENT
Stochastic Process
data is more or less normally distributed
Normal Distribution
used when there is skewness in the data distribution
Log-Normal Distribution
considers further the skewness of the logarithmically transformed hydrologic data; preferred for flood flow frequency; log-normal distribution is a special case of this method
Pearson Type III Distribution
so far gives the best fit for most stations for 1-week, 2-week, 3-week and monthly rainfall totals of the country
Gamma Density Function
that which travels over the ground surface and through the channels to reach the basin outlet
Surface Runoff
that which infiltrates into the soil surface and moves laterally through the upper soil horizons towards streams as perched groundwater above major groundwater level
Interflow
groundwater discharge into a stream due to deep percolation of the infiltrated water into groundwater aquifers
Groundwater Runoff