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Chapter 3 -Hydrology Hwk#3 - pp. 85-87 2,4,7,11 Hydrologic Cycle Runoff - Ground Surface WaterPowerPoint Presentation

Chapter 3 -Hydrology Hwk#3 - pp. 85-87 2,4,7,11 Hydrologic Cycle Runoff - Ground Surface Water

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- Chapter 3 -Hydrology
- Hwk#3 - pp. 85-87 2,4,7,11
- 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)

1. Rainfall

Volume - acre-ft., hectares(ha) (V=Area x depth)

Rainfall intensity - rate at which rain falls

(in/hr. , mm/hr.)

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.

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.

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)

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