Section Seven Hydrology

rainfall measurement recording rain gauges (3)

weighing type , tipping bucket , float type

most accurate method of weighted average methods (thiessen polygon, or isohyetal)

isohyetal method

the duration of design storms used to design water control systems must generally ___ or ____ the time of concentration

equal or exceed

longer the duration of a storm the ___the rainfall intensity

lower

NRCS 24- hour rainfall distributions are the most widely used for simulate a rainfall than actual rainfall events is called what

synthetic hyetograph

the NRCS 24 hour rainfall distribution indicates that the highest rainfall intensity occurs during

the middle period

amount of precipitation that does not contribute to direct runoff due to infiltration, interception, and depression storage

abstractions

portion of the total runoff at a stream that comes from groundwater flow and delayed flow

base flow

portion of rainfall that is available as overland supply (rainfall excess, runoff depth, overland flow)

effective rainfall

the flow that exists before the hydrograph starts rising is contributed by the groundwater and is called (this flow is never included in the hydrograph)

base flow

relationship between DRH and UH shown in the figure , will hold if the rainfall for DRH is ___ a unit

greater than

the peak flow for a 2 inch rainfall for the same duration?

212

effects of rainfall on the watershed can be separately accounted for and accumulated if two unit hydrograph storms occur back to back , their separate responses can be added to produce the composite response of a watershed is called

superpostion

if time to peak tp =1.2 hr what is tb (time base)

1.2 × 2.67

a T-hour UH (has a time base of T hours, has a rainfall excess of 1 inch in T-hours, has time to peak of T hours, has unknown time base)

has a rainfall excess of 1 inch in T-hours

soil group, cover type, and hydrologic condition

factors that affect CN

tc is the travel time of water particle from the ____________ point in the basin to the outflow location

hydraulically remote point

tc is the time to ___ of a catchment under ____ rainfall excess

equilibrium, steady

time of concentration is a function of

intensity, length, slope, and catchment surface

detention basin and retention basins both are considered types of flow _______structures

retardation

impounds the stormwater runoff temporarily and releases it slowly through an outlet structure. Intended to fully drain out following a rainfall event, stores water in a pond or reservior

detention basin

usually larger, and they collect water as a final storage destination. Water is held until it evaporates or infiltrations in the soil

retention basin (wet basin)

used to allow the stored water to percolate into the ground advantage of recharge is that it helps to prevent the depletion of groundwater storage

infiltration basin

blue area is the ____

storage

blue area is the ____

released

which of the following parameters are not required in rational method to calc peak flow (DA, CN, Tc, C)

CN

instrument used to collect and measure precipitation

rain gauge/ hyetometer

used often cause inexpensive, do not give intensity and duration of rainfall during the day, it is measured daily, weekly, monthly

non recording gauges

expensive to install but automatic and produces continues to plot of rainfall against time

recording gauge

gives plot of accumulated rainfall against time, mass curve of rainfall , record gauge, COMMONLY USED

weighing bucket gauge

measured at regular time interavals to provide total rainfall, when .1 inch of rainfall collects in one bucket, record gauge HIGH FREQ RAIN FALL

tipping bucket gague

stream gauging stations collect what four things

collects WSE , discharge, h20 chemistry and temp

stages (wse) can be measured by what two instruments

staff gague or automatic stage recorder

what two insturments can be used to measure velocity

floats (speed=distance over time), and current meter

portion of rain may evaporate as it falls, other portion might be caught on roof or leaves, or other veg. surfaces, loss from a runoff since rain evaporates and never hits the ground

interception

water vaporizes through plant leaves. l transfer of soil moisture from the soil to atmosphere through vegetation

transpiration

direct function of wind and temp, water changes from liquid to gas

evaporation

amount of total precipitation detained in and evaporated from depressions on both the impervious and pervious land surface. water that does not run off or infiltrate. if rainfall exceeds the combined evaporation and infiltration, puddles are developed

depression storage

amount of precipitation that does not contribute to direct runoff due to infiltarion, interception, detention storage and depression storage

abstraction

all rainfall prior to the start of direct storm runoff. both depression and interception storage are depleted during the early part of a storm, and thus a part of this

inital abstraction

effective (excess) rainfall = total rainfall -

abstractions

movement of water from the land surface to upper layer of soil

infiltration

process which water moves through the soil because of gravity

percolation

phi index =

(P-Q )/ storm duration

separate infiltration from rainfall, average rainfall above which rainfall volume is equal to runoff volume

phi index

over land flow is the quanitity of water (intercepted by buildings and vegetative cover, req to fill surface depressions, reaches the stream channels, gets evaporated)

that reaches the stream channels

four primary activities that accelerate erosion

logging, mining, agriculture, construction

raindrop plash and erosion from shallow overland flow

interrill erosion (splash and rill)

widespread dramatic form of soil erosion caused by flow surface erosion, result of the interaction of land use ,climate and slope

gully erosion

soil removal from stream banks

channel erosion

interflow is also known as (subsurface runoff, storm seepage, secondary base flow, all)

all

which of the following parameters are not required in rational method in estimating peak flow (DA, retention potential, tc, C)

retention potential

rainfall excess is = total rainfall -

abstraction (not inital abstraction)

gauging stations monitor the which of the following parameters (stage, discharge, water chem, all)

all

which is NOT a method for measuring stream discharge (area velocity, flow measuring structure, current meter, salt concentration)

current meter

abstractions include which of the following (interception, infiltration, depression storage, all)

all

phi index =

average rainfall intensity (depth) above which volume of rainfall excess equals volume of direct runoff