Hydrologic Overview & Hydrologic Overview & QuantitiesQuantities

It is important to understand the It is important to understand the big picture when attempting to big picture when attempting to

forecast. This includes the forecast. This includes the interactive components and interactive components and

hydrologic quantities.hydrologic quantities.

Hydrologic CycleHydrologic Cycle

The complexity of what we are trying to The complexity of what we are trying to accomplish….accomplish….

Infiltration

Evaporation & Condensation

The Water Budget

Photosynthesis & Respiration

Antecedent Moisture

Conditions

Transpiration & Interception

Variable Source Area

Time of Concentration The “sphere” concept was borrowed

from Dr. Peter Black: Watershed Hydrology – 2nd Edition, Peter Black, 1996, Ann Arbor Press (ISBN# 1-5704 027-1)

Models try to mimic this!Models try to mimic this!

Basin Process Representation

Infiltration

Excess Precip.

Interception

Storage

Time Series Time

Series

From A Basin ViewFrom A Basin View

Excess Precip. Model

Excess Precip.

Basin “Routing”

Runoff HydrographStream

“Routing”

The Runoff PictureThe Runoff Picture• Hydrology is long term and short term….Hydrology is long term and short term….• In this course we will mainly focus on the In this course we will mainly focus on the shortshort term: term:

• Floods & flood flows.Floods & flood flows.• Generating runoff/high flows.Generating runoff/high flows.• Predicting/forecasting flows.Predicting/forecasting flows.• Space/time scales.Space/time scales.

Recipe(s) for a Flood/High Recipe(s) for a Flood/High FlowsFlows• What causes a flood / high flow?What causes a flood / high flow?• What are the conditions?What are the conditions?• What are the types of flooding What are the types of flooding

situations?situations?• Your area or other areas…..Your area or other areas…..

What Are the Defining What Are the Defining Characteristics of a Flood?Characteristics of a Flood?• Timing – rise time, recession, Timing – rise time, recession,

duration.duration.• Flows – peak flows, magnitude Flows – peak flows, magnitude

(statistical).(statistical).• Precipitation – intensity, duration, Precipitation – intensity, duration,

frequency….frequency….

What Controls the Timing, What Controls the Timing, Flow, and Precipitation?Flow, and Precipitation?• The hydrology – short term and long The hydrology – short term and long

term.term.• The meteorology – short term The meteorology – short term

(weather/storm type) and long term (weather/storm type) and long term (climate).(climate).

Short TermShort TermWeather (storm type) & “current Weather (storm type) & “current hydrologic conditions”hydrologic conditions”

Watershed Watershed CharacteristicsCharacteristics

• AreaArea• SlopeSlope• Land UseLand Use• SoilsSoils• GeologyGeology• ClimateClimate• GeomorphologyGeomorphology

Some of the “Right” Some of the “Right” Combinations….Combinations….• Precipitation –vs.- infiltrationPrecipitation –vs.- infiltration

– Precipitation intensity > infiltration ratePrecipitation intensity > infiltration rate– Precipitation total > infiltration capacityPrecipitation total > infiltration capacity– ““Storage” in the system is fullStorage” in the system is full– Human induced high water or flowsHuman induced high water or flows– Natural alterations to the watershedNatural alterations to the watershed

Our Focus - ForecastingOur Focus - Forecasting• Must be both short & long term..Must be both short & long term..• The combination(s) of precipitation The combination(s) of precipitation

and hydrologic conditions that lead and hydrologic conditions that lead create a potential flooding situation…create a potential flooding situation…

• ““basin hydrology” – basin hydrology basin hydrology” – basin hydrology looks at the hydrologic budget in looks at the hydrologic budget in both the short and long term.both the short and long term.

How much water is there?How much water is there?Distribution of Earth's Waters and Residence Distribution of Earth's Waters and Residence

TimesTimes........Location of

Storage Total Water (acre-feet)

Percent of Total

Percent of Fresh

Residence Time

(years) Total water on

earth 1.033 x 1015 100.0

Oceans 1.0 x 1015 96.8 Total Fresh

Water 3.314 x 1013 3.2 100.0 6977

Ice and Glaciers

2.475 x 1013 75.4 5210

Groundwater Deep

4.62 x 1012 14.0 973

Groundwater Shallow

3.63 x 1012 11.0 764

Lakes 9.9 x 1010 0.3 21 Biosphere 8.1 x 1010 0.24 17.1

Soil Moisture 1.98 x 1010 0.06 4.17 Atmosphere 1.155 x 1010 0.035 2.43

Rivers 9.9 x 1010 0.003 2.1

Units & Properties of Units & Properties of WaterWater

Property Symbol Value Comments Density

(mass/volume) ~1.94 slugs/ft3

~ 1.0 g/cm3 Slug = lb*s2/ft

Specific Weight (weight/volume)

62.4 Lbs/ft3

9.81 kN/m3 g

Specific Volume Specific Gravity s.g. 1.0 for water

@ 32.9o F s.g.fluid =

gfluid/gwater Vapor Pressure ~0.4 psi Vapor pressure of

the fluid - not the atmosphere

AreaArea• 1 acre = 43,560 ft1 acre = 43,560 ft22

• 1 mi1 mi22 = 640 acres = 640 acres• 1 hectare = 100m x 100m = 2.471 acres = 10,000 1 hectare = 100m x 100m = 2.471 acres = 10,000

mm22

• 1 km1 km22 = 0.386 mi = 0.386 mi22

Some Common Unit ConversionsSome Common Unit Conversions

VolumeVolume• 1 acre-foot = 1 ac-ft = 1 acre of water x 1 foot 1 acre-foot = 1 ac-ft = 1 acre of water x 1 foot

deep = 43,560 x 1 = 43,560 ftdeep = 43,560 x 1 = 43,560 ft33

• 1 ac-inch = 1 acre x 1 inch deep = 43,560 x 1/12 1 ac-inch = 1 acre x 1 inch deep = 43,560 x 1/12 = 3,630 ft= 3,630 ft33

• 1 ft1 ft33 = 7.48 gallons = 7.48 gallons• 1 gallon H1 gallon H22O ~ 8.34 lbs.O ~ 8.34 lbs.

Runoff VolumeRunoff Volume• 1-inch of runoff over 1 square mile :1-inch of runoff over 1 square mile :• 1/12 feet x 1 mi1/12 feet x 1 mi22 x 640 acres/mi x 640 acres/mi22 x 43,560 x 43,560

ft2/mift2/mi22 = 2,323,200 ft = 2,323,200 ft33

DischargeDischarge• 1 cfs = 1 cubic foot per second1 cfs = 1 cubic foot per second• 1 cfs x 7.48 gal/ft1 cfs x 7.48 gal/ft33 x 3600 sec/hr x 24 hrs/day = x 3600 sec/hr x 24 hrs/day =

646,272 gpd = 0.646 MGD646,272 gpd = 0.646 MGD• 1 cfs x 3600 sec/hr x 24 hrs/day = 86,400 1 cfs x 3600 sec/hr x 24 hrs/day = 86,400

cfs/daycfs/day• 86,400 cfs/day x 1 ac-ft/43,560 ft86,400 cfs/day x 1 ac-ft/43,560 ft33 = 1.983 ac- = 1.983 ac-

ft/day (~ 2 ac-ft/day)ft/day (~ 2 ac-ft/day)• 1.983 ac-ft/day x 12 inches/ft x 1 day/24 hrs = 1.983 ac-ft/day x 12 inches/ft x 1 day/24 hrs =

0.992 ac-in/hr0.992 ac-in/hr• 1 ac-in/hr x 43,560 ft1 ac-in/hr x 43,560 ft33/ac-ft x 1 hr/3600 sec x 1 /ac-ft x 1 hr/3600 sec x 1

ft/12 inches = 1.008 cfsft/12 inches = 1.008 cfs

PowerPower

• Hp = Hp = HQ/550HQ/550• 1 hp = 550 ft*lb/sec = 0.7547 1 hp = 550 ft*lb/sec = 0.7547

kilowattskilowatts

weight of water

H = head or elevation difference

Q = flow

Hydropower wants a lot of flow and a full reservoir…..