Institute for Ag Professionals

Transcription

1 Institute for Ag Professionals Proceedings 2016 Crop Pest Management Short Course & Minnesota Crop Production Retailers Association Trade Show Do not reproduce or redistribute without the written consent of author(s).

2 Impacts of Agricultural Drainage on Water Movement Steven County Historical Society Bruce N. Wilson Bioproducts and Biosystems Engineering University of Minnesota U of M Crop Pest Management Short Course Minneapolis, MN, December 8, 2016

3 Topics Process-based studies Concepts Surface and subsurface Statistical studies Concepts Results

4 Types of Drainage Systems Surface Drainage: Ditches, remove ponded water, outlet for tiles Subsurface Drainage: Tiles, remove water from soil

5 Precipitation Twin Cities 80 Precipitation Departure Average = 27.2 in Cum Departure Year

6 Possible impacts? Flood Flows Flow Rate (cfs) Bankfull Flows Typical Base Flows 100 Lowest Flows 10 1/1/1910 1/1/1930 1/1/1950 1/1/1970 1/1/1990 Year Minnesota River, Mankato

7 Hydrologic Definitions Photo Provided by MN Department of Agriculture 1 sec What is a flow rate of 1 cubic feet per second? 1 ft 1 ft South Branch Root River near Carimona Stage, H H Flow Rate

8 Why we argue Types of drainage: Surface System Subsurface Tile Drainage Photo by Gary Sands Surface and Subsurface Drainage

9 spatial and temporal scale issues Small: Easier to study Large: Of Greater Interest

10 drainage and land use changes Prairie Poorly Drained Corn Impact of Drainage Impact of and Drainage Land Use Corn No Drainage Drainage

11 runoff depth and flow rates Flow Rates (cfs) 1992 Daily Flow For Redwood River Basin Peak Flow Rates Annual Runoff Volume Volume Depth = Wstd Area Small Temporal Scale Q p ~ RO Depth Annual Temporal Scale Q p? RO Depth Event Runoff Depth

12 Most Fundamental Concept: Water Balance p - Precipitation ro = Runoff = sro + gw w - Wells et - Vadose et - Saturated sro Surface r - Recharge o Other flows gw Groundwater ds Deep seepage

13 P ET Annual Runoff Depth Surface Subsurface Water Balance P - ET - RO - DS = S Long-term average: S 0 Typically: DS 0 RO = P - ET DS RO Depth

14 Surface Drainage Steam Digger: Prior to 1910, most ditches dug by team of bulls Study Area Indian Lake (West) Indian Slough (East Indian Lake) Nobles County Ditch 1 (Slope = 0.05%)

15 Junkin Percentage Ditcher (1906), of Ditch 2 tons Constructions of coals/day Blue Earth, Brown, Le Sueur, & Nicollet Ditches of bottom 70 hp width and 30 = 2 hp ft, engines Depth = 3 to 4 ft can usually be dug most cheaply by hand (Roe, 1924) March, 1922 Freeborn & Mower Counties 110 hp, ¼ mile per day, 5 men crew, 12 ft top width, 7 ft deep Prior to 1880 Crookston, MN, ~1900 Usually shallow ditches 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00%

16 P Surface Subsurface ET Annual Runoff Depth Water Balance Surface Drainage Water Balance P - ET - RO - DS = S RO = P - ET Long-term average: S 0 Drainage/Land Typically: Uses Changes DS 0 ETRO = P RO - ET DS RO Depth

17 Impact of Surface Drainage Straightened Channel More rapid runoff Volume Flow Rate Time

18 Robinson s Study General Conclusion: England Flow Rate Surface Drainage 0.15 Surface Grass drainages increase flow rates 0.1 for Open small drains watershed! 0.05 Unit runoff No Channels Time

19 Subsurface Tile Drainage Hand Installation Common for Tile

20 Machine Trenching at Crookston in 1903 Average cost - $1.24 per 100 ft, 6 hp, $1400 roots, sticky soil problems DesignRocks, Charts 6 ft depth 14 inch tile: 90 hour per 100 ft 14 inch 6 feet Gary SandsGary Sands

21 Subsurface Drainage: Wilson Farm 4 inch clay tile. Clay tile degraded because of soil conditions Ground Human dug (6 concrete) Machine installed (6 concrete, 90 ft spacing)

22 Subsurface Drainage 1966 SCS Design Spacing=90 ft Indian Slough C1-C9 D1-D9 B1-B9 Concrete Tile: 6 in: 58,150 ft (11 miles) 8 in: 1,433 ft 10 in: 550 ft 12 in: 34 ft Plastic Tile ~1968 Wilson Farm After in Plastic tile Net = 45 ft A1- A6

23 P Surface Subsurface ET Annual Runoff Depth Subsurface Drainage Water Balance Water Balance RO P -= ET P - ET RO - DS = S Long-term Drainage/Land average: Use S 0 Typically: DS 0 ET RO RO = P - ET Drainage Only DS RO Depth ET RO

24 Tile Drainage? Straightened Channel Peak Flow RO Flow Rate Slower Runoff Response Tile Drainage Time

25 More Insight Surface: Fast Gravity Gravity Net Pressure Macropore Weight (Gravity) Pressure Small Pore Small Area Pore Area Large Friction Shorter Forces Distances Pressure Gravity (~100%) after long time Base: Slow Friction Subsurface: Moderate Friction Velocity and Length Friction Cross-sectional Area Moderate Pipe Area Long Travel Smaller Time Friction Forces Smaller Net Pressure Relatively Large Old Flow Area Water Smaller Friction Forces Gravity dominate force Only 5% of force for S=5%

26 Drained Plot Example: Peat - Finland, July 7 Undrained Plot Water Table 10 cm July 7 Storage difference 40 mm Drained Undrained Water Table 42 cm Discharge 10 Storage Capacity 5 60 Drained Undrained Depth (cm) Date (June and July)

27 Istok and King s Study Western Oregon Wtsd size: 6 ha and 1.4 ha 4 years of data Winter wheat Low-moderate intensity storms 10 cm tile, 12 m spacing

28 Discharge (l/sec) Discharge (l/sec) Watershed 4 Time (Hours) Watershed 2 Surface Watershed 4 Watershed 2 Watershed 2 Tile Line Time (Hours)

29 Return Period = 10 yr, P for Twin Cities 100% area at drainage coefficient Rational C = 0.5 CN = 75 and Type II Storm 10 Rational Method Q p = C I A Q p /A = C I Peak Flow (in/h) SCS TR 55 Drainage Coefficient D c = 1/8 to 1 in/day 0.92 in/h 0.02 in/h 0.28 in/h Time of Concentration (h)

30 Sponge Effect 1000 Surface Surface Fast Flow Rate Drain Time Subsurface Flow Rate Base Flow Slow Time

31 Simulation Approaches Maximum Evapotranspiration Ag Production Channel Only Current Pre-drainage Model of Moore and Larson Two wtsds in Jackson County 1957 to 1962 Tile line Overland Flow Precipitation Surface drainage using tile inlets Stream Channel Water Table Annual runoff in inches for the Little Sioux River Little Sioux River Peak Discharges in cfs, 30 May 1959

32 Potential Flaws in Logic Closed Basins No Surface Outlet Land Surface Important Proposition : Subsurface drainage decreases surface flow?

33 Scaling to Larger Watersheds Wtsd 1 Wtsd 2 Total Flow Rate Wtsd 2 Wtsd Time

34 Straightened Channel Continued New Total Original Wtsd 1 Wtsd 2 Flow Rate Wtsd 2 New 1 Wtsd Time

35 Outflow (mm/hr) acres Surface Subsurface Day Outflow (mm/hr) acres Surface Subsurface Day Outflow (mm/hr) Surface 4 sq mi Subsurface Outflow (mm/hr) Surface 24 sq mi Subsurface Day Day

36 Summary: Process Arguments Complex system Small watersheds Surface drainage: Increases flooding Subsurface drainage: Decrease or minor increase Large watersheds Even more complex Trends may be different

37 Topics Process-based studies Concepts Surface and subsurface Statistical studies Concepts Results

38 Trends With Time Row Spacing (inches) Acreage of Crops (in thousands) Corn Wheat 1000 Barley 20 Runoff Seeding Rate 12,440 seeds/ac Flow Rate 30,400 seeds/ac Time Soybeans Hay Oats Year Data: Vern Cardwell Year Data Provided by Steven Taff

39 Minnesota River - Mankato Annual Peak Flow Rate (cfs) Conclusion: Weather dominate factor 2014: 67,300 cfs 1881: 110,000 cfs 20 year average Time (Year) 2015: 13,700 cfs

40 Trends Between Watersheds Real World Big Small Soil A Soil B Extrapolate Flow Rates for Return Periods Regression Analysis Flow Rate = f(precipitation, Size, Soil, Drainage)

41 Example: Moore & Larson Seventy-three watersheds Iowa, Minnesota, South and North Dakota Mean annual flood Watershed characteristics Area, Slope, Lake and Marsh Area

42 All Watersheds Q = 74.8 (Area) (% Lakes) Regression Rate cfs Perfect Fit Line Observed Rate Wilson s Experiences: Precise regressions are difficult for watersheds

43 Twenty-three Selected Watersheds Q = 58.4 (Area) (% Lakes) Example ( average watershed): Initial Watershed Conditions: Area = 265 sq mi, % Lake = 4.5% Q = 1077 cfs Impact of Drainage: % Lake = 2.25% Q = 1406 cfs Approximately 30% Increase

44 Summary: Statistical Large annual variability in peak flows with time: * Climate dominate factor * Slight increase in flows after climate adjustments Large variability in flows among similar watersheds: * Reduction in percentage of lakes/marshes increases flows * Conversion to row crops increases flows * Magnitude of increase is difficult to determine

45 Questions?