Water Budget for Evaluating Wetland Hydrology Restoration and Determination Chapter 6

1. Water Budget for Evaluating Wetland Hydrology Restoration and Determination Chapter 6

2. Water Budget - good for humid regions- precipitation and runoff main inputs- evapotranspiration main losses- wetland is depression

3. Water Budget - Simple spreadsheet - Computer Program - SPAW - DRAINMOD

6. Simple Water Budget S = I- L where, S = change in storage I = Inputs L = Losses

7. Simple Water Budget Timeframe - Hourly (data seldom available) - Daily (good for determinations and restoration) - Weekly (good for restoration) (weak for determination) - Monthly (OK for restoration) (inadequate for determination)

8. Simple Water Budget Inputs (I=P + R) - P=Direct Rainfall (rain into wetland) - R= Runoff (rainfall runoff from drainage areas into wetland) - Groundwater Discharge (extremely difficult to quantify) - Flooding from streams and rivers (difficult to account for in water budget)

9. Simple Water Budget Losses (L = O+ET+SW+DP)- O= Outflow (surface water in excess of depression storage capacity) - ET = Evapotranspiration (evaporation and transpiration) - SW = Soil water storage (soil dependent) - DP = deep percolation (extremely difficult to quantify, contribution to groundwater recharge)

10. Simple Water Budget Storage (S) - capacity to store water (size and shape dependent) - storage is normally recorded in depth ( inches, feet, cm, m) - all inputs and outputs must be in same units as storage

11. Data Requirements - Daily precipitation data from a representative climate station (30 years) - Daily pan evaporation data from a representative climate station (30 years) - Soils data, on-site soil profile description - land cover and land use information

12. Calculations 1) To initial or previous day’s water level add 2) Direct Precipitation (P) 3) Runoff (R) using the SCS Runoff Curve Number (CN) Method - Curve Numbers can be changed through the growing season to represent cover condition changes - Antecedent Rainfall Condition can be tracked to modify CN for consecutive days of rainfall

13. Calculations 1) To initial or previous day’s water level subtract 2) Surface Outflow (O) 3) Evapotranspiration (ET) 4) Soil water storage (SW) 5) Groundwater recharge (DP)

14. Calculations 1) Calculate change in storage (S=I-L) and compute end of day water level 2) Calculate daily water level for period of record (ex. 30 years) 3) Plot daily water level and evaluate hydroperiod fluctuations in relation to planned hydroperiod , especially in regard to flora and fauna needs. - For precipitation driven system, the depth of storage is normally the only variable (outflow crest height, depth of macrotopographic features) that can be varied to alter hydroperiod. - In some cases additional runoff can be introduced to system to increase inputs. Outputs are normally fixed.

18. Direct precipitation, 12 inches maximum storage, no contributing drainage area. Result is many periods will be dry, water is not permanent. To make water more permanent, increase storage depth or add recharge area using diversions, etc.

19. Direct precipitation, 24 inches maximum storage, no contributing drainage area. Result is fewer periods will be dry, water is not permanent. To make water more permanent add recharge area using diversions, etc.

20. Direct precipitation and contributing drainage area, 24 inches maximum storage. Result is few periods will be dry, water is permanent.

24. Comparison of Spreadsheet and SPAW water budgets with measured water levels. Cracking soils cannot be totally addressed .