rainfall runoff management cnmp core curriculum section 4 – manure wastewater storage and handling

Rainfall Runoff Management

CNMP Core CurriculumSection 4 – Manure Wastewater

Storage and Handling

CNMP Development Core Training Curriculum

These course materials have been developed as a cooperative effort between five land-grant universities and The Natural Resources Conservation Service.

Ames, Iowa 50011, (515) 294-4111.

Copyright © 1995-2006, Iowa State University of Science and Technology. All rights reserved.

Copyright Information

Objectives

1. Keep the clean water clean

2. Recognize rainfall runoff effects on:

• storage volume in liquid manure systems

• application logistics and nutrient content

Required Materials

• Animal Waste Management Field Handbook, Part 651, Chapter 10, Agricultural Waste Management System Component Design.

• NRCS Conservation Practice Standard 558 Roof Runoff Structure.

• Supplemental Resources

– AWM and NOAA addresses and resources


Divert Clean Water

Rainfall Runoff ManagementClean Water Diversion


Roof Runoff


Runoff Volume Characteristics

1. Rainfall Amount2. Infiltration3. Evaporation 4. Drainage Area

Rainfall Runoff Factors to Consider:

1. Normal precipitation from runoff area

2. Normal precipitation minus evaporation on Storage Structure

3. Emergency Storm from runoff areas

4. Emergency Storm on Storage Structure

Runoff Management

Normal Precipitation and Evaporation is based on County and Weather Station rainfall record data.

Runoff volume is based on this climate data and Runoff Curve Number information.

Normal Precipitation

Climate Data Sources:

*AWM

Software

*NOAA

*State or Local

Month Prec. (in) Evap. (in)

January 4.73 1.60

February 4.32 1.90

March 5.85 3.00

April 4.24 4.00

May 4.82 4.90

June 3.80 5.50

July 5.08 5.60

August 3.86 5.20

September 3.41 4.30

October 3.29 2.90

November 4.27 1.80

December 4.83 1.70

Totals 52.50 42.40

Typical

AWM Data:

State: TN

County: Loudon

Station: TN5158

25 Yr, 24-Hr Storm Event: 5.6 inches

Evaporation

Storage and treatment facilities require an

allowance for precipitation less evaporation for the

most critical design period.

Evaporation

Evaporation

Factors effecting free water surface evaporation

1. Effects of salinity2. Coloration3. Floating surface material, such as bedding or crusting

Local records are available for average monthly evaporation.

The Runoff (Q) Equation Factors

• Q = Runoff in inches

• P = Rainfall in inches

• Ia = Initial abstraction in inches

• S = Potential maximum retention after runoff begins in inches

Runoff Curve Number (RCN or CN)

• CN = 1000/(10 + S)

• The RCN’s were developed by examining rainfall runoff data from small agricultural watersheds

Runoff Depth for selected CN’s and rainfall amounts

Rainfall (in) CN=60 CN=80 CN=95

4.0 0.76 2.04 3.43

6.0 1.92 3.78 5.41

8.0 3.33 5.63 7.40

Infiltration

Cover description

Curve Numbers forhydrologic soil group

Cover type & hydrologic condition A B C D

Pasture, grassland, or range, good condition 39 61 74 80

Bare soil, pervious areas, no vegetation 77 86 91 94

Impervious areas, paved lots, roofs, driveways 98 98 98 98

InfiltrationRunoff Factors:

*soil hydrologic characteristics

*type of cover

Infiltration

Runoff Curve Number (RCN) of 90 is representative of

an unpaved or unsurfaced feedlot

A paved or surfaced feedlot typically has a

RCN of about 97

Infiltration

(Runoff from an earth feedlot near Dallas, TX.)

Month Precip Runoff(inches) % (inches)

Oct. 3.18 36 1.14Nov. 2.60 27 0.7Dec. 2.34 24 0.56Jan. 1.96 20 0.39Feb. 2.57 20 0.51Mar. 3.04 22 0.67

Total 3.97

Class Example:

• Calculate the runoff depth from a 6-inch rainfall:

1. On a pasture with good hydrologic conditions and “B” hydrologic soil group

2. For an unsurfaced feedlot with a RCN of 90

(Hint: look at slide #19 & #20)

Class Example:

1. From slide 19- CN is 61; & slide 18 with CN of 61, the runoff depth can be interpolated for the 6-inch rainfall to be 2.01 inches

2. From slide 18, CN of 90, the runoff depth from interpolation is 4.86 inches

(Note: same rainfall, over twice runoff on feedlot)

Determining Runoff Volume• Runoff Volume is dependent on:

– Surface area– Rainfall depth– Surface type (paved vs. unpaved)

• Maps in Appendix 10C of AWMFH can be used to determine runoff volumes from surfaced or unsurfaced feed lots– Surfaced, CN 97– Unsurfaced, CN 90

Determining Runoff Volume

Runoff Volume =

Surface Area (ft2) x Rainfall (ft) x (% Runoff from Surface ÷ 100)

In-Class Exercise

A 6.0 acre open beef feedlot is being constructed near Ames, IA. The annual rainfall at Ames, IA is 30 inches. The earthen portion of the lot is 5.5 acres, and the concrete portion is 0.5 acres. Using the Annual Runoff charts for surfaced (CN 97) and unsurfaced (CN90) feedlots, determine the volume of runoff that will leave the 6 acre feedlot in Ames, IA.

In-class Exercise

1 acre = 43,560 ft2

Concrete Area _______ ft2

Earthen Lot Area _______ ft2

Annual Rainfall _______ ft

CN 90 Runoff Percentage ______ %

CN 97 Runoff Percentage ______ %

In-class Exercise

• Concrete Area 21,780 ft2

• Earthen Lot Area 239,580 ft2

• Annual Rainfall 2.5 ft

• CN 90 Runoff Percentage 23 %

• CN 97 Runoff Percentage 55 %

Runoff Volume = Area x Rainfall x (CN % Runoff ÷ 100)

Total Runoff Volume = Runoff Volume earthen + Volume of Runoff

concrete

In-class ExerciseRunoff Vol.earthen= Area x Rainfall x (CN 90 % Runoff ÷ 100)

= 239,580 ft2 x 2.5 ft x 0.23 = 137,760 ft3

Runoff Vol. concrete= Area x Rainfall x (CN 97 % Runoff ÷ 100)

= 21,780 ft2 x 2.5 ft x 0.55 = 29,950 ft3

Total Runoff Vol. = Runoff Vol. earthen + Runoff Vol.concrete

= 137,760 ft + 29,950 ft = 167,710 ft3

Runoff Management

AWM uses a more conservative approach to estimating runoff from runoff areas as compared to tables in AWMFH. AWM includes a climate database with monthly precipitation and evaporation.

Runoff Management

AWM allows input based on Pervious and Impervious watershedImpervious - concrete, roofsCurve Number of 98 - cannot be modifiedPervious - manure pack or other CN of 90 - can modify

Emergency Storm Runoff Variables

1) Depth of 25- year, 24-hour storm on storage structure

2) Depth of 25-year, 24-hour storm from runoff areas to storage structure

4 Components of Runoff

12

34

Determining Rainfall Runoff Amounts

Site Visit – Sample CNMP Dairy

Identify Areas that contribute runoff


To Storage pond


Rainfall on Open and

Concrete Lots

Roof Area

Roof Area


Runoff from roofs

Rainfall on Storage Structure


Concrete Areas that Contribute

Runoff


Silage Bunker Runoff - Condition when Full

Drain- to storage pond

Silage Bunker - Condition when

empty

Runoff =

6000 ft2

To Storage pond


Impervious Areas Roof Runoff : 10,000 ft2

Concrete Lot: 13,100 ft2

Roofed Feedbunk: 1,320 ft2

Silage Bunker: 6,000 ft2 Total: 30,420 ft2



Total

30,420 sf

1. Assuming a sufficient storage of 90 days.

2. What can we do to reduce runoff into the storage structure and increase the storage period?

3. Why would you need more than 90 days of storage?


1. What can we do to reduce runoff into the storage structure and increase the storage period?

• Enlarge pond, gutter roof, diversions

2. Why would you need more than 90 days of storage?

• Land application restraints, climate, crop needs, etc


Critical Storage Interval

• Based on initial site conditions, the critical storage interval for the sample CNMP

dairy was determined to be 151 days, November - March

What If we Gutter 10,000 sq ft?


20,420 ft2

Adequate storage for 120 to 150 days; enough to survive critical winter months of Dec

thru March

by Guttering


115,980 cu. Ft. (all runoff areas)

-77,850 cu. Ft.

38,130 cu. Ft. (clean water removed)

38,130 cu. Ft. x 7.48 gallons/ cu. Ft. = 285,212 gallons

Benefits of Guttering:

1) 10 to 12 hours less pumping per year

2) storage period is increased (120 to 150 days)

3) low cost ($6.00 linear foot)

$6.00 x 150 linear feet = $1000 to $2000

How much clean water is removed by guttering?


What if we install more roofs & gutters?


10,420 ft2

Adequate storage for 180 days; IDEAL

by

Guttering and Roofing


115,980 cu. Ft. (runoff from all areas)

-39,730 cu. Ft.

76,250 cu. Ft. (clean water removed)

76,250 cu. Ft. x 7.48 gallons/ cu. Ft. = 570,350 gallons

Benefits of Roofing & guttering:

1) 20 hours less pumping per year

2) storage period is increased

Disadvantage:

COST - $5.00 sq. ft. x 10,000 sq. ft. = $50,000

Roofing?


GIVEN: It was determined that existing storage capacity is not adequate to last through winter months.

SOLUTION: Look at the previous alternatives and discuss each with the decision-maker.

Decision-maker's Alternatives

Decision-maker's Alternatives

Alternatives:

>>>>

#1

Increase storage

structure

#2

Gutter existing roof (10,000 sf)

#3

#2 plus additional roofing & guttering

(10,000 sf)

Objectives met: >>>>

Increased storage

Increased storage (to 120-150 days)

Reduced pumping time

Increased storage (to 180 days)

Reduced pumping time

Cost: >>>> Moderate

$15k-$20k

Low

$6/ linear ft

$1k-$2k

High

Roof $5/sq ft = $50k + $2 = $52k

Runoff Management Summary1. Keep the clean water clean (diversions, roofs &

gutters)

2. Evaluate and appropriately collect contaminated runoff into storage structures or properly treat runoff from the heavy use areas (pervious or impervious)

3. Consider the effect of rainfall runoff on application logistics and nutrient content of the waste material

4. Design a runoff management system with adequate capacity

Questions

or

Comments?

Gutter Design Procedure

1) Compute the capacity of the selected gutter size

2) Compute the capacity of the downspout

3) Determine whether the system is controlled by the gutter capacity or downspout capacity and adjust number of downspouts if desired

4) Determine the roof area that can be served

Gutter Position

Gutter Design

Final Step:

•Adequate discharge pipeline or trough based on gutter/downspout design capacity

•Material Quality

rainfall runoff management cnmp core curriculum section 4 – manure wastewater storage and handling

Documents

evaporation slide

rainfall runoff data

rainfall runoff factors

runoff areas

rainfall runoff effects

runoff depth

local slide

driveways98 slide