Chapter 3 -Hydrology Hwk#3 - pp ,4,7,11 Hydrologic Cycle Runoff - Ground Surface Water Infiltration - Ground Penetration (percolation) Transpiration - Water goes through vegetation and then is released into the air as vapor Evapotranspiration - Is the combination of evaporation and transpiration (>50% of precipitation)

Rainfall intensity - rate at which rain falls (in/hr., mm/hr.) Chapter 3 -Hydrology 1. Rainfall Volume - acre-ft., hectares(ha) (V=Area x depth) Recurrence Interval (N) years - the average time span between identical storms over a long period of time (i.e. 5 year storm- same as return period) Probability of occurence (1/N) - is the statistic of occurence in a single year

Chapter 3 -Hydrology 2. Surface Water A. Water Sheds Drainage Basin - Land which contributes runoff to a river or stream Confluence - the point at which two streams converge Tributary - streams that feed into a first-order stream Subbasin Tributary Drainage Basin Outlet

Chapter 3 -Hydrology 2. Surface Water B. Streamflow Discharge - Volume per unit time Hydrograph - flow response of a stream for a particular rainfall event (fig.3.15) Perennial - streams that have a base flow from ground water Intermittent or Ephemeral Stream-Streams that dry up after the rainfalls Stage - the water surface above a referenced level Weir - used to measure volume flow rate Droughts - a long period of dry weather MA7CD10 Flow - Minimum Average 7 Consecutive Day 10 - year flow - 90% chance that the minimum weekly discharge will be greater than the MA7CD10. Design parameter for water pollution control projects.

Chapter 3 -Hydrology 3. Reservoirs Summation Hydrograph - Determines when the reservoir is filling up or what is the minimum required storage volume. (fig. 3.20) Uniform Withdrawal or Yield Line - Is the amount of water the reservoir can supply in a specific time period without going dry. (Predetermined by the demand on the reservoir) Minimum Storage Volume Req’d - The minimum volume of water required in the reservoir in order to prevent a drought from depleting it. Sediments behind a Dam - Causes a problem for vegetation and wildlife who rely on warmer temperatures and nutrients from silts and other deposited materials.

Chapter 3 -Hydrology 4. Aquifers & Well Points Aquifers - Is an underground stream.(fig 3.26) Well Points - Perforated pipes that penetrate underground acquifers or water table Darcy Law - V= K X S where K - permeability coeff., mm/s V - Flow velocity, mm/s S - slope of the water table Drawdown - The elevation distance between the pumping level and the static level.(fig. 3.28)