Water Demand & Flow Calculations

Water Demand&

Flow Calculations

Lokhaze AliVisiting Faculty

NICE, SCEE, NUST

Water Demand & Flow Calculations 2

Thought of the Day


Water Use

Water use can be distinguished into three different types

1. Withdrawals or Abstractions2. Consumptive Water Use3. Non-Consumptive Water Use


Withdrawals or Abstractions

• Where water is taken from a surface or groundwater source

• after use returned to a natural water body

• e.g. water used for cooling in industrial processes returned to a river

• such return flows are important for downstream users


Consumptive Water Use• Water consumption that starts

with a withdrawal or an abstraction but in this case without any return flow

• water abstracted that is no longer available for use

• it has evaporated, transpired, been incorporated into products and crops

• consumed by man or livestock or otherwise removed from freshwater resources

• e.g. water use include steam escaping into the atmosphere and water contained in final products i.e. it is water that is no longer available directly for subsequent uses




Non-Consumptive Water Use

• Water withdrawn for use that is not consumed

• e.g. water withdrawn for purposes such as hydropower generation

• recreational activities• boating or fishing

where the water is still available


Water demand

• Volume of water requested by users to satisfy their needs

• Often considered equal to water consumption

• Conceptually the two terms do not have the same meaning

• In rural parts of Pakistan, the theoretical water demand considerably exceeds the actual consumptive water use

The 4 S’s: Some Common Terms

• Water Shortage - absolute shortage where levels of available water do not meet certain defined minimum requirements.

• Water Scarcity - a more relative concept describing the relationship between demand for water and its availability.

• Water Stress - the symptomatic consequence of scarcity which may manifest itself as increasing conflict over sectoral usage, a decline in service levels, crop failure, food insecurity etc..

• Water Security - a situation of reliable and secure access to water over time.


Water Scarcity

Water scarcity category and associated problems

Volume of water available(m3/person/year)

Beyond the “water barrier”: continual, wide-scale water supply problems,

becoming catastrophic during droughts.

< 500

Chronic water scarcity: continual water supply problems, worse during annual dry

seasons; frequent severe droughts.

500 to 1,000

Water stressed: frequent seasonal water supply and quality problems, accentuated

by occasional droughts.

1,000 to 1,666

Moderate problems: occasional water supply and quality problems, with some adverse effects during severe droughts

1666 to 10,000

Well-watered: very infrequent water supply and quality problems, except during

extreme drought conditions.

> 10,000


Water Use• Agricultural use - Any use or

activity involving agriculture, including irrigation

• Commercial use - The use of water by a place of business, such as a hotel, restaurant, or office building. This does not include multi-family residences or agricultural, industrial, or institutional users

• Industrial use - The use of water in processes designed to convert materials of a lower order of value into forms having greater usability and commercial value, and the development of power by means other than hydroelectric, but does not include agricultural use

• Residential use - The use of water that is billed to single and multi-family residences, which applies to indoor and outdoor uses


Top 10 Freshwater Consumers


World Water Use by Sector

Source: OECD Environmental Outlook Baseline, 2007


Typical Water Use at Home

Shower 2 gallons per minute

Teeth brushing <1 gallon, especially if water is turned off while

brushing

Hands/face washing 1 gallon

Dishwasher 4 to 10 gallons/load

Dishwashing by hand 20 gallons

Clothes washer 25 gallons/load

Toilet flush 3 gallons

Outdoor watering 5 to 10 gallons per minute


Residential Gallons Per Capita Per Day

Residential gallons per capita per day = (Residential Use ÷ Residential Population) ÷ 365 • Residential Use = Single-Family Use + Multi-Family Use • Residential Population = the residential population of the service area. Includes only single- and multi-family populations


Commercial Use


Water Data USGS


Water Demand US


Estimating Water Withdrawals for Livestock

Wt = ((Pdc * Cdc) + (Pbc * Cbc) + (Ph * Ch) + (Plh * Clh) + (Pbh * Cbh) + (Pt * Ct) + (Ps * Cs) + (Pg * Cg) + (Pe * Ce)) / 1,000,000where Wt = total water withdrawals, in million gallons per day; Pdc = Number of dairy cows; Cdc = Coefficient for dairy cows, in gallons per day; Pbc = Number of beef and other cattle; Cbc = Coefficient for beef and other cattle, in gallons per day; Ph = Number of hogs and pigs; Ch = Coefficient for hogs and pigs, in gallons per day;

Plh = Number of laying hens; Clh = Coefficient for laying hens, in gallons per day; Pbh = Number of broilers and other chickens; Cbh = Coefficient for broilers and other chickens, in gallons per day; Pt = Number of turkeys; Ct = Coefficient for turkeys, in gallons per day; Ps = Number of sheep and lambs; Cs = Coefficient for sheep and lambs, in gallons per day; Pg = Number of goats; Cg = Coefficient for goats, in gallons per day; Pe = Number of horses, ponies, mules, burros, and donkeys; and Ce = Coefficient for horses, ponies, mules, burros, and donkeys, in gallons per day.


Water-use coefficients for Livestock


Different crops contribution to total water footprint of crop production Period: 1996–2005


The Green, Blue, Grey and Total Water Footprint of Crop Production

Period 1996-2005


Urban Water Demandin

California to 2100

Case Study


Urban Water Use


Commercial & Industrial Water Use


Simple Linear Forecasts


Global Surface Warming & Population Projections


Time Series of Decadal Average Water Use for Six Simulations


Simulated Urban Water Use under Scenarios of Conservation and

Population


Flow Calculations


Conversion Factors

Multiply By To obtain

gallon (gal) 3.785 liter (L)

gallon (gal) 0.003785 cubic meter (m3)

million gallons (Mgal)

3,785 cubic meter (m3)

gallon per day (gal/d)

0.003785 cubic meter per day (m3/d)

million gallons per day (Mgal/d)

0.04381 cubic meter per second (m3/s)


Flow Calculations

Flow is expressed in the English system of measurements using many terms. The most common terms are:

gpm - gallons per minute cfs - cubic feet per second gpd - Gallons per day MGD - Million gallons per day

Flow Conversions Flow rates can be converted to different units using the conversion process. The most common flow conversions are:

1 cfs = 449 gpmand1 gpm = 1,440 gpd


Flow Calculations

gpd to MGDTo convert gallons per day (gpd) to MGD, divide the gpd by 1,000,000 gallons or 106. For example:

Convert 125,000 gpd to MGD.125,000 gpd = 0.125 MGDOr

convert 2,300,000 gpd to MGD2,300,000 gpd = 2.3 MGD

MGD to gpmThere are many instances where the design or plant information is given in MGD and we wish to have the flow in gpm. This conversion is accomplished in two steps.For Example:Convert 0.125 MGD to gpmStep 1) Convent to gpd by multiplying by 1,000,0000.125 x 1,000,000 = 125,000 gpdStep 2) Convert to gpm by dividing by the number of minutes in a day (1,440 min/day). 125,000 gpd = 86.8 or 87 gpm


Detention Time

Detention time is the amount of time that a fluid stays in a container.

Detention time is expressed in units of time. The most common are: seconds, minutes, hours and days.

Detention Time = Volume Flow Rate

For example: 1) if the flow is in gpm then the detention time will be in minutes; or2) if the flow is in gpd, then the detention time will be in days.

Sample CalculationThe reservoir for the town is 85,000 gallons. The well will produce 55 gpm. What is the detention time in the tank in hours.Solution:DT = 85,000 gallons = 1,545 min

55 gpmor1,545 minutes = 25.8 hrs 60 minutes/hr


Water Tanks


Examples


Examples


Home Assignment

1. A tank is 20' x 60' by 15' deep. What is the volume in gallons?

2. A tank is 60' in diameter and 22' high. How many gallons will it hold?

3. A tank is 82' in diameter and 31 feet high. The flow is 1600 gpm. What is the detention time in hours?

4. A tank is 120' x 50' x 14' deep. The flow is 2.8 mgd. What is the detention time in hours?


Safe Drinking Water for ALL

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Water Demand & Flow Calculations