Unit Hydrographs Class 14: Unit Hydrographs Topics and Goals: Learning 1

Class 16: Direct Runoff (DRO) and Unit Hydrographs Class 14: Unit Hydrographs Topics and Goals: Learning 1. Calculate volume of DRO from a hydrograph; Objectives 2. Complete all steps to develop a Unit Hydrograph. Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph

Ocean Class 14: Unit Hydrographs

Learning Objectives

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Timing parameters Hydrographs Learning Objectives

tc Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

- Duration of rainfall excess (D): time from start to finish of rainfall excess Calculating - Lag time (L or tp) : time from the center of mass of rainfall excess Direct Runoff to the peak of the hydrograph (DRO)

- Time of rise (TR) : time from the start of rainfall excess to the peak of the hydrograph Example: Develop Unit - Time of concentration (tc) : time for a wave (of water) propagate from Hydrograph the most distant pt in the watershed to the outlet. One estimate is time from the end of net rainfall to the inflection pt.

- Time base (Tb) : total duration of the DRO hydrograph Class 14: Unit Unit Hydrograph Hydrographs

Learning Objectives

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Assume Example: linear Develop Unit response Hydrograph Class 14: Unit Constructing the Unit Hydrograph Hydrographs

Learning Objectives

From your text (BHV, p. 117): Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Separating Baseflow Hydrographs

Learning Objectives

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Volume (depth) of DRO? Hydrographs

Learning Objectives

From BHV, p. 117: Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Hydrographs In-Class Exercise: Volume (depth) of DRO? Learning Use DRO hydrograph to calculate volume of DRO; one approach is the “trapezoidal Objectives rule” -- see E2-1(d) in handout (posted)

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit For a 2600-acre basin, what is the amount (depth) of DRO? Hydrograph Hints: (a) sum up the total volume in cfs-hour; (b) 1 cfs = 1 ac-in / hour Class 14: Unit Net Rainfall (Excess Rainfall) = DRO Hydrographs

Learning Objectives

From BHV, p. 117: Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Net Rainfall (Excess Rainfall) = DRO Hydrographs

Learning Objectives

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph

The phi-index is an assumed uniform and constant infiltration rate. It’s calculated by finding the loss difference between gross precipitation and observed surface runoff. Class 14: Unit Net Rainfall (Excess Rainfall) = DRO Hydrographs If the phi-index of the storm is 0.5 inches per hour for 5 Learning Objectives hours, then what is the net rainfall?

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Net Rainfall (Excess Rainfall) = DRO Hydrographs If the phi-index of the storm is 0.5 inches per hour for 5 Learning Objectives hours, then what is the net rainfall?

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Net Rainfall (Excess Rainfall) = DRO Hydrographs

Learning Objectives • DRO = Excess rainfall is the cumulative Hydrograph rainfall minus rainfall abstractions; Anatomy estimates runoff volume (important for (components)

storage design) What is the Unit Hydrograph?

• Influencing factors: rain amount, How do you construct the drainage area, soil type, ground cover Unit HG?

Calculating Direct Runoff • Curve Number approach developed by (DRO) Soil Conservation Service (now Natural Example: Resources Conservation Service, or Develop Unit NRCS) to estimate daily excess rain Hydrograph amount from daily rain amount (we’ll tackle this in week 8) Class 14: Unit Constructing the Unit Hydrograph Hydrographs

Learning Objectives

From your text (BHV, p. 117): Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Constructing the Unit Hydrograph Hydrographs

Learning Objectives

From your text (BHV, p. 117): Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Constructing the Unit Hydrograph Hydrographs

Learning Objectives

From your text (BHV, p. 117): Hydrograph Anatomy (components)

What is the Unit Hydrograph?

How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Hydrographs

Learning Objectives

Hydrograph Anatomy The Unit Hydrograph (components) is a depiction of the hydrograph What is the Unit (discharge) that Hydrograph? would result from 1.0 inch of rainfall. How do you construct the Unit HG? The upshot: you normalize an Calculating Direct Runoff observed hydrograph (DRO) to produce the UH. Example: Develop Unit Hydrograph Class 14: Unit Constructing the Unit Hydrograph Hydrographs

Learning 1) Use DRO hydrograph to calculate total DRO Objectives (“trapezoidal rule”) Hydrograph Anatomy (components)

2) Convert DRO hydrograph to Unit hydrograph: in this What is the example, because total volume of DRO is 2 inches (2 Unit inches x watershed area = volume), divide the Hydrograph? ordinate (y-axis) values of discharge by 2, to How do you normalize the values to a set of values that would construct the produce only 1 inch of DRO -- this becomes the unit Unit HG? hydrograph. Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph Class 14: Unit Hydrographs

Learning Objectives

Hydrograph Anatomy (components)

What is the In-Class Exercise: Unit Hydrograph? Unit Hydrograph Development How do you construct the Unit HG?

Calculating Direct Runoff (DRO)

Example: Develop Unit Hydrograph For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph: In-Class Exercise: Unit Hydrograph Development

For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

This example problem is example #2-1 on page 108 (Ch. 2) of Bedient.... For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

A ~100 cfs baseflow is evident. For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

A ~100 cfs baseflow is evident - use constant discharge method. For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph: For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

See spreadsheet for calculations.... For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph: For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

For a phi-index of 0.5 in/hour, subtract that from the hyetograph.

For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

For a phi-index of 0.5 in/hour, subtract that from the hyetograph. This yields a net excess rainfall of 1 in/hour for 2 hours = 2 inches. For an 1850-acre watershed with a phi-index of 0.5 inches/hour, convert the following hydrograph into a 2-hour unit hydrograph:

Net Rainfall = 2.0”

DRO = 2” Net Rainfall = 2.0”

DRO = 2”

Based on the UH, what are (a) Tb, (b) tp, and (c) tc? Net Rainfall = 2.0”

DRO = 2”

Based on the UH, what are (a) Tb, (b) tp, and (c) tc? Timing parameters

- Duration of rainfall excess (D): time from start to finish of rainfall excess

- Lag time (L or tp) : time from the center of mass of rainfall excess to the peak of the hydrograph

- Time of rise (TR) : time from the start of rainfall excess to the peak of the hydrograph - Time of concentration (tc) : time for a wave (of water) propagate from the most distant pt in the watershed to the outlet. One estimate is time from the end of net rainfall to the inflection pt.

- Time base (Tb) : total duration of the DRO hydrograph Based on the UH, what are (a) Tb, (b) tp, and (c) tc?

Net Rainfall = 2.0”

tc DRO = 2”