OUTFLOW COMPONENTS

Evapotranspiration (EVAP) l Evapotranspiration is the result of surface water and soil evaporation and transpiration from the plants within the depressional basin. l Since the precise period when the seven day ponding or fourteen day saturation will change from year to year, it cannot be assumed that the evaporation or evapotranspiration rate will the the maximum rate during the growing season.

Some Sources of EVAP Data l NRCS Field Office Technical Guide (FOTG) or in the Irrigation Field Guide. l The FAO Modified Blainey Criddle method (FAO Paper 24) l Annual Free Water Surface Evaporation map in the NOAA Tech. Report Nation Weather Service (NWS) 33, “Evaporation Atlas for the Contiguous 48 United States”

Conversion of Mean Annual Evaporation l To facilitate conversion of the average annual evaporation rate to monthly rates, a percentage-by-month can be generated using NOAA Technical Report NWS 34, “Mean Monthly, Seasonal and Annual Pan Evaporation for theUnited States,: dated December 1982.

Steps for EVAP Chart 1. The first column of the chart are the months 2. Obtain the monthly percentage 3. Compute the average monthly average EVAP 4. Compute the average daily EVAP rate for each month. 5a) compute the EVAP for the number of days for the critical duration b) Sum the EVAP for the total number of months and divide this number by the number of months used.

Example 6 Calculating Average EVAP l For the site used in Example 1, A site located at the southeast corner of Morton County, Kansas Step 1. the Average Annual Evaportation is: 67 inches

Calculating Average EVAP continued Step 2. The WETS Table shows the 50% chance, 28 degree killing frost free period to be 4/9 thru 10/26. The monthly percentages for Kansas are as follows: MonthPercent April 9 May 12 June 14 July 15 August 14 Sept. 10 October 7

Calculating Average EVAP continued Steps 3, 4 & 5: Figure for 7-Day Ponding (critical period = 7 days) Month Daily Ave. 7-Day Ave. Month % (INCHES) (INCHES) (INCHES) April May June July August Sept Oct Total Daily Average: 0.25 in. 7-Day Average EVAP: 1.84 in.

Soil WATER (SW) l The soil moisture is the total water that the soil can hold when saturated, without any water standing above the soil surface.

Available Water Holding Capacity l AWC can be used for the total soil moisture, unless one believes that the soil is at wilting point (15 bar pressure) at the time that the critical period begins. »If this is the case then additional water would need to be added to go from 1/10 bar to soil saturation.

Example 7 Soil Water Holding Capacity HORIZONDEPTH(in/in) (in) A Bt Total 2.16 »If the 10 percent additional water is added SW = AWC x 1.10 = 2.16 x 1.1 = 2.38 in.

Deep Percolation l Any water movement starting at the ground surface and moving down below the root zone is classified as deep percolation

Example 8 -- Deep Percolation PERM i = perm. rate (in/hr) x 24 hr/da x (i) days i = critical duration for deep perc. for i = 7 days PERM 7 = perm. rate (in/hr) x 24 hr/da x 7 days perm. rate = in/hr = in/hr x 24 hr/da x 7 days = 0.34 in.

Outflow Equation l Outflow = (EVAP n + SW + PERM i ) x P a where n = number of days evap i = critical duration for infiltration P a = depression bottom surface area

Example 9 Outflow Calculation l Using the site used in Example 1, located at thesoutheast corner of Morton County, Kansas, with a depression bottom surface area of 1.0 acres Outflow = (EVAP 7 + SW + PERM 7 ) x P a = ( )in. x 1.0 ac = 4.56 ac-in

Example of a Water Balance

Water Balance l For hydrology component of Wetland Delineation to meet Inundation: Inflow - Outflow>=0.00 ac-in (for specific period) Inflow = (R O / P s ) + (R d x P a ) Outflow = (EVAP n + SW + PERM i ) x P a

Example Water Balance Inflow = (5.00 / 1.13) + (2.95 x 1.0) = 7.37 ac-in Outflow = ( )in. x 1.0 ac. = 4.34 ac-in w/ 30% additional to AWC = ( )in. x 1.0 ac. = 4.56 ac-in Inflow - Outflow = = ac-in w/ 30% additional to AWC Inflow - Outflow = = ac-in

Maximum Depression Surface Area P a-max = DA x (50% chance RO) = _____ Acres (EVAP n +SW+PERM i - R d ) x P s P a-max = Maximum Acres allowed in Wetland with existing inputs

Example 11 - Maximum Depression SurfaceArea P a-max = ( 25 x 0.20 ) = 6.9 Acres ( ) x 1.13

Minimum Drainage Area (A D ) l A D = [(EVAP n + SW + PERM i - R d ) x P s RO

Example 12 Minimum Drainage Area l Usng Example 10 and asuming 10% addition to AWC A D = ( ) x = 9.1 acres/wetland acre

Example Kimball Co. The site is a playa depression l Given: RO = 0.08 ac-in/ac l RCN = 81 l DA = 34 acres l Rd = 2.26 in. l EVAP = 27 in/year ( make chart below) l PERM = in/hr l SW = 2.36 in.

Minimum Ponding... Given the above informatiion, what is the minimum ponding depth required to offset losses for seven (7) days? Min. water depth = Total Outflow (losses) Outflow = (EVAP7 + SW + PERM7 ) x Ps = ( ) x 1.13 = ____ in. Example EVAP MONTH % OF Annual Monthly Et 7-days Et BY MONTH INCHES INCHES l APRIL 6 ______ ______ l MAY 13 ______ ______ l JUNE 19 ______ ______ l JULY 25 ______ ______ l AUGUST 21 ____________ l SEPTEMBER 13 ______ ______ l OCTOBER 3 ______ ______ l TOTAL ______ l AVERAGE Evapotranspiration (EVAP 7 ) ______(total/7mo.)

Minimum Ponding... Given the above informatiion, what is the minimum ponding depth required to offset losses for seven (7) days? Min. water depth = Total Outflow (losses) Outflow = (EVAP7 + SW + PERM7 ) x Ps = ( ) x 1.13 = ____ in. Example 13 Minimum Ponding Depth Given the above informatiion, if surveying the depression to find the wetland surface area, what is the minimum ponding depth required to offset losses for seven (7) days? l Min. water depth = Total Outflow (losses) Outflow = (EVAP 7 + SW + PERM 7 ) x Ps l = ( ) x 1.13 = ____ in.

Example Problem l What is the maximum playa depression near level bottom surface area that will meet the wetland criteria of 7 days ponding and minimum drainage area per acre of wetland?? l Use a depression shape factor P s of 1.13

Example Max. Wetland Area l P a-max = DA x (50% chance RO) = ____ ac (EVAP 7 +SW+PERM 7 -R d )xP s l P a-max = 34 x 0.08 = ____ ac ( )x1.13

Example Minimum A D l A D = [(EVAP 7 + SW + PERM 7 - R d ) x P s RO l A D = ( ) x 1.13 = ____ ac 0.08

Questions and Review

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