Ag Drainage Design Protocols and Current Technology

Transcription

1 Department of Agricultural and Biosystems Engineering Ag Drainage Design Protocols and Current Technology Matthew Helmers Dean s Professor, College of Ag. & Life Sciences Associate Professor, Dept. of Ag. and Biosystems Eng. Iowa State University

2 Estimated Percent of Area Benefitting from Drainage Source: Dan Jaynes and David James USDA-ARS

3 Estimated Nitrate-N Loss, January to June for Source: David et al., 2010

4 1920 CENSUS OF AGRICULTURE

5 J.B. Crim Farm Nov 15,1916 end of 54 inch block tile in northern Boone Co.

6 Required Drainage Capacity Drained Area = A (acres) Flowrate (Q) = DC x A DC = Drainage Coefficient Drainage Coefficient Amount of water that can be removed in a 24 hour period

7 Drainage Design Majority of Des Moines Lobe is artificially drained with tile drainage systems installed in early to mid-1900 s From surveys performed in 1980 s many drainage systems have a drainage coefficient of <0.25 in/day (some <0.10 in/day) Modern drainage systems will be designed with a drainage coefficient of in/day

8 Situation Drainage systems will be redesigned and constructed in the future Question remains whether they are designed to the status quo or designed to modern design standards and to increase environmental services (i.e. integrated with wetland systems)? Integrating wetlands at the drainage design stage allows for additional wetland sites since depth and grade of drainage system can be altered to incorporate a wetland

9 Integrated Drainage Wetland Landscape Systems Extent of drainage will not be increased Drainage district main network would be redesigned and the drainage coefficient improved to allow for greater infiltration of water Field-scale modeling (DRAINMOD) conducted to this point to evaluate potential impact of existing versus redesigned outlet capacity on field export of water Future studies would evaluate drainage district scale impacts (size of acres)

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11 Impacts of Drainage Design Annual Flow Annual average discharge (cm) ss (kg/ha) Subsurface Drainage Surface Runoff Drainage coefficient (in/day) Estimated Nitrate-N Concentrations subsurface drainage = 13.3 mg/l surface runoff = 1 mg/l Estimated Total P Concentrations subsurface drainage = 0.1 mg/l surface runoff = 1.6 mg/l oss (kg/ha)

12 Predicted Daily Surface Runoff 10 0 Daily surface runoff (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) /1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

13 Predicted Daily Subsurface Drainage Daily subsurface drainage (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) 1/1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

14 Predicted Daily Discharge Surface + Subsurface 10 0 Daily discharge - combined surface and subsurface (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) /1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

15 Predicted Daily Discharge Surface + Subsurface Daily discharge - combined surface and subsurface (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) Daily discharge - combined surface and subsurface (cm) 1/1/ /1/82 3/1/82 4/1/82 5/1/82 6/1/82 7/1/82 8/1/82 9/1/82 10/1/82 11/1/82 12/1/82 D.C. = 0.25 cm/day D.C. = 0.95 cm/day 1/1/ Daily precipitation (cm) 1/1/91 2/1/91 3/1/91 4/1/91 5/1/91 6/1/91 7/1/91 8/1/91 9/1/91 10/1/91 11/1/91 12/1/91 1/1/92

16 Department of Agricultural and Biosystems Engineering Drainage District Scale Modeling

17 MIKE SHE Components Water Module Topography Climate Landuse Soil water movement Overland flow Unsaturated flow Saturated zone Drainage Channel flow

18 The PAL3 and PAL5 watersheds Similar watersheds in the upper Des Moines lobe of Northcentral Iowa Similar watershed characteristics Area (1128 ha and 1356 ha) Elevation 400 m above sea level Slope 0-2% with 0.5% avg Soils lowland Canisteo and Clarion-Nicollet-Webster Almost exclusively agricultural land use Heavily tile drained throughout -Stars indicate watershed outlets

19 Model Definition Time period Overland flow Finite difference methods Max 1 hour time step Unsaturated zone Richard s equation Max 1 hour time step Saturated zone flow Finite difference methods Max 4 hour time step Grid cell size 30 x 30 m Topography defined by 3 m LiDAR [meter] Topography [meter] [meter] Above Below Undefined Value

20 Meteorological Inputs Time period from Rainfall data Collected from 4 local sources Most representative 2 were used (Emmetsburg and Swea City) Evapotranspiration data Kanawha station FAO Penman-Montieth equation

21 Vegetative Inputs Land use spatiotemporally variable Corn, soybeans, perennial grassland Continuous corn and 2 year corn-soybean rotation All non crop ground modeled as perennial grassland

22 Model Validation Watershed PAL 5

23 Model performance during validation Year of PAL5 watershed Observed streamflow (mm) Simulated streamflow (mm) PBIAS EF R Total PBIAS percent bias based on daily flow; EF Nash-Sutcliffe coefficient based on daily flow; R 2 coefficient of determination based on weekly flow Department of Agricultural and Biosystems Engineering

24 Drainage Time Constant PAL 3

25 Department of Agricultural and Biosystems Engineering Drainage Infrastructure

26 PAL5 water balance comparison of current conditions to row crop agriculture without drainage infrastructure PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PAL5 Current Conditions Row crop agriculture without drainage infrastructure PPT ET Δ_S OVL SUBD TOT ET Δ_S OVL SUBD TOT Mean Department of Agricultural and Biosystems Engineering

27 No Drainage Current Land Use

28 Department of Agricultural and Biosystems Engineering Land Use Change

29 PAL5 water balance comparison of current conditions to grassland with drainage infrastructure PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PAL5 Current Conditions Land use conversion to perennial grassland with drainage infrastructure PPT ET Δ_S OVL SUBD TOT ET Δ_S OVL SUBD TOT Mean Department of Agricultural and Biosystems Engineering

30 Land use conversion to all perennial grassland with drainage infrastructure

31 Department of Agricultural and Biosystems Engineering Presettlement?

32 PAL5 water balance comparison of current conditions to likely pre-settlement conditions PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PAL5 Current Conditions Pre-settlement conditions, perennial grassland with no drainage infrastructure PPT ET Δ_S OVL SUBD TOT ET Δ_S OVL SUBD TOT Mean Department of Agricultural and Biosystems Engineering

33 Land use conversion to all perennial grassland without drainage infrastructure

34 Drain Capacity Study in 1980 s investigated drainage in the Des Moines River Basin Drain capacity of many drainage district mains evaluated Example: Calhoun County Avg. drainage coefficient of 38 mains was 0.18 in/day Range in drainage coefficient from 0.05 to 0.44 in/day

35 How much do Under Designed Systems Impact Yield? These estimates are likely on the conservative side. Relative Yield (%) Webster Nicollet Okoboji Yield impacts are likely greater Drainage Coefficient (in/day)

36 Example Yield Increases Calhoun District Size (acres) Outlet Capacity (in/day) Relative Yield Inc in Rel. Yield if 0.5 in/day coefficient

37 Iowa Conservation Reserve Enhancement Program (CREP) Targeted Wetland Restoration Corn Soybean DD Tile 1 km W.G. Crumpton, Iowa State University

38 Drainage Main Systems Drainage district main systems are ageing As systems age out what will be done with replacement Integrating drainage redesign with installation of wetlands may be something to consider in the future Five pilot projects in place examining integrating drainage redesign and wetlands Department of Agricultural and Biosystems Engineering

39 Department of Agricultural and Biosystems Engineering Discussion Matt Helmers Dean s Professor, College of Agriculture & Life Sciences Associate Professor Extension Agricultural Engineer, Ag and Biosystems Engineering Iowa State University, Ames IA (515) mhelmers@iastate.edu

40 Hydrologic Impacts of Drainage: Field to Drainage District Scale Matt Helmers Department of Agricultural and Biosystems Engineering, Iowa State University

41 Background After recent floods in Iowa, the hydrologic impacts of drainage systems have been questioned Need for analysis on how land management and drainage impact water flow both rate and amount Need for a watershed model that can represent prairie pothole landscape

42 Department of Agricultural and Biosystems Engineering Drainage Modeling at the Field- Scale in Iowa using DRAINMOD calibrated to Gilmore City Drainage

43 Impacts of Drainage Design Annual Flow Annual average discharge (cm) oss (kg/ha) Subsurface Drainage Surface Runoff Drainage coefficient (in/day) Estimated Nitrate-N Concentrations subsurface drainage = 13.3 mg/l surface runoff = 1 mg/l Estimated Total P Concentrations subsurface drainage = 0.1 mg/l surface runoff = 1.6 mg/l 0.8 Loss (kg/ha) Department of Agricultural 0.7 and Biosystems Engineering 0.6

44 Daily Discharge (cm) Daily Precipitation (cm) Daily Discharge (cm) Daily Precipitation (cm) /10/ /17/91 5/24/91 Date 5/31/91 DC = 0.05 in/day DC = 0.10 in/day DC = 0.37 in/day DC = 0.50 in/day 6/7/91 DC = 0.05 in/day DC = 0.10 in/day DC = 0.37 in/day DC = 0.50 in/day 6/14/ Impacts of Drainage Design on Total Daily Discharges (surface runoff + subsurface drainage) /1/82 5/8/82 5/15/82 Date 5/22/82 5/29/82 6/5/82 20

45 Daily Discharge (cm) Daily Precipitation (cm) Daily Discharge (cm) Daily Precipitation (cm) /10/ /17/91 5/24/91 Date 5/31/91 DC = 0.05 in/day DC = 0.10 in/day DC = 0.37 in/day DC = 0.50 in/day 6/7/91 DC = 0.05 in/day DC = 0.10 in/day DC = 0.37 in/day DC = 0.50 in/day 6/14/ Impacts of Drainage Design on Total Daily Discharges (surface runoff + subsurface drainage) /1/82 5/8/82 5/15/82 Date 5/22/82 5/29/82 6/5/82 20

46 Department of Agricultural and Biosystems Engineering Drainage District Scale Modeling

47 Why do we get less surface runoff?

48 MIKE SHE Components Water Module Topography Climate Landuse Soil water movement Overland flow Unsaturated flow Saturated zone Drainage Channel flow

49 The PAL3 and PAL5 watersheds Similar watersheds in the upper Des Moines lobe of Northcentral Iowa Similar watershed characteristics Area (1128 ha and 1356 ha) Elevation 400 m above sea level Slope 0-2% with 0.5% avg Soils lowland Canisteo and Clarion-Nicollet-Webster Almost exclusively agricultural land use Heavily tile drained throughout -Stars indicate watershed outlets

50 Model Definition Time period Overland flow Finite difference methods Max 1 hour time step Unsaturated zone Richard s equation Max 1 hour time step Saturated zone flow Finite difference methods Max 4 hour time step Grid cell size 30 x 30 m Topography defined by 3 m LiDAR [meter] Topography [meter] [meter] Above Below Undefined Value

51 Meteorological Inputs Time period from Rainfall data Collected from 4 local sources Most representative 2 were used (Emmetsburg and Swea City) Evapotranspiration data Kanawha station FAO Penman-Montieth equation

52 Vegetative Inputs Land use spatiotemporally variable Corn, soybeans, perennial grassland Continuous corn and 2 year corn-soybean rotation All non crop ground modeled as perennial grassland

53 Drainage Time Constant PAL 3

54 Model performance during testing of PAL3 watershed with daily streamflow Year Observed streamflow (mm) Simulated streamflow (mm) PBIAS EF (%) R Total PBIAS percent bias based on daily flow; EF Nash-Sutcliffe coefficient based on daily flow; R 2 coefficient of determination based on weekly flow Department of Agricultural and Biosystems Engineering

55 Model performance during validation Year of PAL5 watershed Observed streamflow (mm) Simulated streamflow (mm) PBIAS EF (%) R Total PBIAS percent bias based on daily flow; EF Nash-Sutcliffe coefficient based on daily flow; R 2 coefficient of determination based on weekly flow Department of Agricultural and Biosystems Engineering

56 Model Validation Watershed PAL 5

57 Water balance for PAL5 over the simulation period ( ) PPT precipitation; ET evapotranspiration; Re subsurface recharge; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PPT ET Re ΔS OVL SUBD Error Total (mm) (mm) (mm) (mm) (mm) (mm) (mm) Flow (mm) Mean

58 Department of Agricultural and Biosystems Engineering Land Use Change

59 PAL5 water balance comparison of current conditions to grassland with drainage infrastructure PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PAL5 Current Conditions Land use conversion to perennial grassland with drainage infrastructure PPT ET Δ_S OVL SUBD TOT ET Δ_S OVL SUBD TOT Mean Department of Agricultural and Biosystems Engineering

60 Land use conversion to all perennial grassland with drainage infrastructure

61 Department of Agricultural and Biosystems Engineering Drainage Infrastructure

62 PAL5 water balance comparison of current conditions to row crop agriculture without drainage infrastructure PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PAL5 Current Conditions Row crop agriculture without drainage infrastructure PPT ET Δ_S OVL SUBD TOT ET Δ_S OVL SUBD TOT Mean Department of Agricultural and Biosystems Engineering

63 No Drainage Current Land Use

64 Department of Agricultural and Biosystems Engineering Presettlement?

65 PAL5 water balance comparison of current conditions to likely pre-settlement conditions PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Year PAL5 Current Conditions Pre-settlement conditions, perennial grassland with no drainage infrastructure PPT ET Δ_S OVL SUBD TOT ET Δ_S OVL SUBD TOT Mean Department of Agricultural and Biosystems Engineering

66 Land use conversion to all perennial grassland without drainage infrastructure

67 Discussion The MIKE SHE modeling is still a work in progress Simulations seemed to represent hydrologic response fairly well Perennial land use decreased total water outflow Removing the drains increased the peak flow Department of Agricultural and Biosystems Engineering

68 Department of Agricultural and Biosystems Engineering

69 Percent (%) change from baseline values for PAL3 and PAL5 with land use change to all perennial grassland without drainage (presettlement) Year PAL3 percent (%) change from baseline values PAL5 percent (%) change from baseline values ΔET Δ_S ΔOVL ΔSUB ΔTOT ΔET Δ_S ΔOVL ΔSUB ΔTOT Mean PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Department of Agricultural and Biosystems Engineering

70 Percent (%) change from baseline values for PAL3 and PAL5 with land use change to all perennial grassland with drainage Year PAL3 percent (%) change from baseline values PAL5 percent (%) change from baseline values ΔET Δ_S ΔOVL ΔSUB ΔTOT ΔET Δ_S ΔOVL ΔSUB ΔTOT Mean PPT precipitation; ET evapotranspiration; ΔS change in subsurface storage; OVL surface runoff; SUBD subsurface drainage Department of Agricultural and Biosystems Engineering

71 Scenario Summary and Conclusions Scenario conditions PAL3 PAL5 Surface flow change (%) Drainage flow change (%) Total Flow change (%) Perennial grassland decreases total flow (or row crop increases total flow) Drainage decreases surface flow and peak flow events Surface flow change (%) Drainage flow change (%) Total Flow change (%) Current conditions Perennial grass, with drainage Perennial grass, pre-settlement Shallow drainage Row crop, no drainage Shallow drainage changes allocation of surface and subsurface flow, but not total flow No drainage increases overland flow, total flow, and the number and severity of peak flow events throughout growing season

72 Drainage Redesign Impacts on Water Flow Matt Helmers Department of Agricultural and Biosystems Engineering, Iowa State University

73 Questions How does tile drainage alter downstream water flow? How do modifications in the main channel stream alterations impact downstream water flow?

74 Background Earliest published account of debate of drainage is 1861 at the Institution of Civil Engineers in London A. Marston published on this topic in 1909 M. Robinson and D.W. Rycroft have synthesized data on impacts in a chapter in Agricultural Drainage, Agronomy Monograph No. 38

75 Debate about overall impacts of drainage on streamflow Significant debate due to lack of appropriate data and as such much of the discussion has been speculative Impacts on flow may occur at multiple scales including: Field scale Catchment scale Combines field scale and main channel improvements

76 Discussion from the Chapter on The Impact of Drainage on Streamflow Consideration of the impact of drainage on streamflow needs to identify the point of interest field scale, along the main channel of the stream, or at the catchment scale Field-scale for sites with natural high water table conditions the drainage will increase soil water storage capacity hence infiltration is increased thereby reducing surface runoff and peak storm flows. Source: Agricultural Drainage, Agronomy Monograph No. 38

77 Discussion from the Chapter on The Impact of Drainage on Streamflow Cont d Main channel effects of modifying main channels by cleaning, straightening and deepening main channels has potential to increase peak flows because of reduction of overbank storage and faster travel times. Source: Agricultural Drainage, Agronomy Monograph No. 38

78 Discussion from the Chapter on The Impact of Drainage on Streamflow Catchment Scale Considerations Catchment-scale flows from different sub catchments will influence the peak flows and the relative importance of field drainage and main channels will vary depending on storm size Field drainage likely to be dominant for small and medium storms Main channel improvements dominant for large events Source: Agricultural Drainage, Agronomy Monograph No. 38

79 Is the Starting Point Important? Some discussions of drainage have focused on systems with and without drainage Less discussion on impacts of modification to tile or subsurface drainage after other alterations have all ready been made This would more truly reflect case of improving the capacity of the drainage main

80 Required Drainage Capacity Drained Area = A (acres) Flowrate (Q) = DC x A DC = Drainage Coefficient Drainage Coefficient Amount of water that can be removed in a 24 hour period

81 Drainage Design Modern drainage systems would be designed with a drainage coefficient of in/day From surveys performed in 1980 s many drainage systems have a drainage coefficient of <0.25 in/day (some <0.10 in/day)

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83 Integrated Drainage Wetland Landscape Systems Drainage district main network would be redesigned and the drainage coefficient improved Field-scale modeling (DRAINMOD) conducted to this point to evaluate potential impact of underdesigned versus redesigned outlet capacity on field export of water Future studies would evaluate drainage district scale impacts (size of acres)

84 North Carolina Study Used DRAINMOD coupled with a stream routing model to evaluate impacts of drainage practices on water outflow at various scales Evaluated Conventional drainage open field ditch spaced 100 m apart Improved subsurface drainage using tile drains spaced 22.5 and 33.5 m apart

85 Average Annual Water Balance Averaged over Two Soils (Average rain = 110 cm) Drainage Plan ET (mm) Total outflow (mm) Surface runoff (mm) Subsurface flow (mm) Average Water Table Depth (mm) Conventional Improved

86 Effect of Watershed Size and Drainage on Three-Year Return Period Storm Drainage Plan Watershed Size (ha) ,036 6,216 Peak Daily Flow Rate (mm/day) Conventional Improved

87 Drainage Modeling at the Field-Scale in Iowa using DRAINMOD calibrated to Gilmore City Drainage

88 Impacts of Drainage Design Annual Flow Annual average discharge (cm) ss (kg/ha) Subsurface Drainage Surface Runoff Drainage coefficient (in/day) Estimated Nitrate-N Concentrations subsurface drainage = 13.3 mg/l surface runoff = 1 mg/l Estimated Total P Concentrations subsurface drainage = 0.1 mg/l surface runoff = 1.6 mg/l oss (kg/ha)

89 Predicted Daily Surface Runoff 10 0 Daily surface runoff (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) /1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

90 Predicted Daily Subsurface Drainage Daily subsurface drainage (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) 1/1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

91 Predicted Daily Discharge Surface + Subsurface 10 0 Daily discharge - combined surface and subsurface (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) /1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

92 Predicted Daily Discharge Surface + Subsurface Daily discharge - combined surface and subsurface (cm) D.C. = 0.25 cm/day D.C. = 0.95 cm/day Daily precipitation (cm) Daily discharge - combined surface and subsurface (cm) 1/1/ /1/82 3/1/82 4/1/82 5/1/82 6/1/82 7/1/82 8/1/82 9/1/82 10/1/82 11/1/82 12/1/82 D.C. = 0.25 cm/day D.C. = 0.95 cm/day 1/1/ Daily precipitation (cm) 1/1/91 2/1/91 3/1/91 4/1/91 5/1/91 6/1/91 7/1/91 8/1/91 9/1/91 10/1/91 11/1/91 12/1/91 1/1/92

93 Impacts of Depth to Groundwater Table 0 Depth to the water table (in) Drainage coefficient = 0.05 in/day Drainage coefficient = 0.10 in/day Drainage coefficient = 0.38 in/day 120 1/1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 0 Date Daily Average Depth to Water Table D.C. of 0.05 in/day 42 in D.C. of 0.1 in/day 46 in D.C. of 0.37 in/day 49 in Depth to the water table (in) Drainage coefficient = 0.05 in/day Drainage coefficient = 0.10 in/day Drainage coefficient = 0.38 in/day 120 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95 1/1/96 1/1/97 1/1/98 1/1/99 1/1/00 Date

94 Impacts of Depth to Groundwater Table 0 Depth to the water table (in) Drainage coefficient = 0.05 in/day Drainage coefficient = 0.10 in/day Drainage coefficient = 0.38 in/day 100 1/1/82 2/1/82 3/1/82 4/1/82 5/1/82 6/1/82 7/1/82 8/1/82 9/1/82 10/1/82 11/1/82 12/1/82 1/1/83 Date 0 Depth to the water table (in) Drainage coefficient = 0.05 in/day Drainage coefficient = 0.10 in/day Drainage coefficient = 0.38 in/day 100 1/1/91 2/1/91 3/1/91 4/1/91 5/1/91 6/1/91 7/1/91 8/1/91 9/1/91 10/1/91 11/1/91 12/1/91 1/1/92 Date

95 Daily Discharge (cm) Daily Precipitation (cm) Daily Discharge (cm) Daily Precipitation (cm) /10/ /17/91 5/24/91 Date 5/31/91 DC = 0.05 in/day DC = 0.10 in/day DC = 0.37 in/day DC = 0.50 in/day 6/7/91 DC = 0.05 in/day DC = 0.10 in/day DC = 0.37 in/day DC = 0.50 in/day 6/14/ Impacts of Drainage Design on Total Daily Discharges (surface runoff + subsurface drainage) /1/82 5/8/82 5/15/82 Date 5/22/82 5/29/82 6/5/82 20

96 Drain Spacing Surface Runoff (D.C. = 3.5 cm/day) 12 0 Daily surface runoff (cm) Drain spacing = 24 m Drain spacing = 150 m Daily precipitation (cm) /1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

97 Drain Spacing Subsurface Drainage (D.C. = 3.6 cm/day) Daily subsurface drainage (cm) Drain spacing = 24 m Drain spacing = 150 m Daily precipitation (cm) 1/1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

98 Drain Spacing Combined Discharge (D.C. = 3.6 cm/day) 12 0 Daily discharge - combined surface and subsurface (cm) Drain spacing = 24 m Drain spacing = 150 m Daily precipitation (cm) /1/80 1/1/81 1/1/82 1/1/83 1/1/84 1/1/85 1/1/86 1/1/87 1/1/88 1/1/89 1/1/90 1/1/91 1/1/92 1/1/93 1/1/94 1/1/95

99 Drain Spacing Combined Discharge (D.C. = 3.6 cm/day) Daily discharge - combined surface and subsurface (cm) Daily discharge - combined surface and subsurface (cm) /1/ /1/91 2/1/82 2/1/91 3/1/82 3/1/91 4/1/82 4/1/91 5/1/82 5/1/91 6/1/82 6/1/91 7/1/82 7/1/91 8/1/82 8/1/91 Drain spacing = 24 m Drain spacing = 150 m 9/1/82 10/1/82 11/1/82 12/1/82 Drain spacing = 24 m Drain spacing = 150 m 9/1/91 10/1/91 11/1/91 12/1/91 1/1/83 1/1/ Daily precipitation (cm) Daily precipitation (cm)

100 Additional Comments Despite modified drainage there would still be depressional storage on the land While potential to decrease surface runoff that doesn t necessarily mean decreased flooding but improved subsurface drainage should have little impact on flooding

101 Drainable Porosity Degree of saturation Degree of saturation