# Presentation: 663701

## Hydrologic Overview & Quantities

- It is important to understand the big picture when attempting to forecast.  This includes the interactive components and hydrologic quantities.

## Hydrologic Cycle

- Precipitation

- Interception

- Evapotranspiration

- Infiltration

- Runoff

- Streamflow

- Storage

## The complexity of what we are trying to 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!

**Basin Process Representation**

**Infiltration**
**Excess Precip.**
**Interception**
**Storage**

**Time Series**

**Time Series**

## From A Basin View

**Excess Precip. Model**

**Excess Precip.**

**Basin “Routing”**

**Runoff Hydrograph**

**Stream “Routing”**

## The Runoff Picture

- Hydrology is long term and short term....
- In this course we will mainly focus on the ***short*** term:
- Floods & flood flows.
- Generating runoff/high flows.
- Predicting/forecasting flows.
- Space/time scales.

## Recipe(s) for a Flood/High Flows

- What causes a flood / high flow?
- What are the conditions?
- What are the types of flooding situations?
- Your area or other areas.....

## What Are the Defining Characteristics of a Flood?

- Timing – rise time, recession, duration.
- Flows – peak flows, magnitude (statistical).
- Precipitation – intensity, duration, frequency....

## What Controls the Timing, Flow, and Precipitation?

- The hydrology – short term and long term.
- The meteorology – short term (weather/storm type) and long term (climate).

## Short TermWeather (storm type) & “current hydrologic conditions”

## Watershed Characteristics

**Area**
**Slope**
**Land Use**
**Soils**
**Geology**
**Climate**
**Geomorphology**

## Some of the “Right” Combinations....

- Precipitation –vs.- infiltration
- Precipitation intensity > infiltration rate
- Precipitation total > infiltration capacity
- “Storage” in the system is full
- Human induced high water or flows
- Natural alterations to the watershed

## Our Focus - Forecasting

- Must be both short & long term..
- The combination(s) of precipitation and hydrologic conditions that lead create a potential flooding situation...
- “basin hydrology” –  basin hydrology looks at the hydrologic budget in both the short and long term.

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

## Units & Properties of Water

## Area

**1 acre = 43,560 ft****2**
**1 mi****2**** = 640 acres**
**1 hectare = 100m x 100m = 2.471 acres = 10,000 m****2**
**1 km****2**** = 0.386 mi****2**

_**Some Common Unit Conversions**_

## Volume

**1 acre-foot = 1 ac-ft = 1 acre of water x 1 foot deep = 43,560 x 1 = 43,560 ft****3**
**1 ac-inch = 1 acre x 1 inch deep = 43,560 x 1/12 = 3,630 ft****3**
**1 ft****3**** = 7.48 gallons**
**1 gallon H****2****O ~ 8.34 lbs.**

## Runoff Volume

**1-inch of runoff over 1 square mile :**
** ****1/12 feet x 1 mi****2**** x 640 acres/mi****2**** x 43,560 ft2/mi****2****  = 2,323,200 ft****3**

## Discharge

**1 cfs = 1 cubic foot per second**
**1 cfs x 7.48 gal/ft****3**** x 3600 sec/hr x 24 hrs/day = 646,272 gpd = 0.646 MGD**
**1 cfs x 3600 sec/hr x 24 hrs/day = 86,400 cfs/day**
**86,400 cfs/day x 1 ac-ft/43,560 ft****3**** = 1.983 ac-ft/day (~ 2 ac-ft/day)**
**1.983 ac-ft/day x 12 inches/ft x 1 day/24 hrs = 0.992 ac-in/hr**
**1 ac-in/hr x 43,560 ft****3****/ac-ft x 1 hr/3600 sec x 1 ft/12 inches = 1.008 cfs**

## Power

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

****weight of water
**H = **head or elevation difference
**Q = **flow
- Hydropower wants a lot of flow and a full reservoir.....