NREM 407/507 - March 26 1. Yellow River Presentation today Nile River next Tuesday 2. Calculate stream bank erosion, gully erosion and sheet and rill erosion for the Swenson Farm that we visited on Tuesday in Lab. 3. Lab next week channel and flood plain dynamics or use of a stream visual assessment protocol to asses present condition if you have waders you could bring them along. 4. Tests will be returned for sure on Tuesday Paraguay & Parana Rivers International Rivers Project Syr Darya & Amu Darya Aral Sea Niger/Benue Ganges Mekong/Tonle Sap Tigris & Euphrates Yellow River Rising Limb Stormflow Peak Flow Rate Antecedent Flow Rate Baseflow Falling Limb Stormflow 1
Use the Channel Evolution Model to describe what is happening and why to this bank What is this? What channel locations do are these people standing on? What NPSP sources do you see here? What is the dynamics of this location? In the bottom picture what is the future of this finger of land? 2
Use the Channel Evolution Model to describe what is happening and why to this bank Caught in the Act! Trying to sneak out of Class Hanson Gully Watershed - Erosion Estimation Project Bear Creek What influences surface erosion & gully formation? Ephemeral gully Hog Confinement First Stop Rainfall intensity/duration Soil erosivity Hillslope gradient Hillslope length Land-use Oxbows Big Gully Nick Point Gully Confluence With Bear Creek How do we estimate the contribution of surface erosion and gully erosion to sediment load of Bear Creek Spillville Coland 62E 2 Nicollet 62E 2 Storden 62D 2 Clarion 2 D 2 Webster Storden 62D 2 138C2 Clarion Hanson Gully Topo Map Hanson Gully Soils Map 3
1. We will estimate the amount of erosion taking place Tools for Assessing Erosion in Watersheds Handout Universal Soil Loss Equation for Sheet & Rill USLE A = RKLSCP A = soil loss (tons of soil moving per acre) R = rainfall erosivity index (US & Iowa Maps) C = cropping management K = soil erodibility index (Soil Survey Lab) factor (Tables) P = erosion-control factor L = hillslope-length factor (Fig 15-19/Table) (Tables) S = hillslope-gradient factor (Fig 15-19/Table) Hanson Gully Watershed Data Table p 4 Lab Soil Mapping Name Slope K Hydrologic Land acres Unit Erosion Class Capability 62D2 Storden 9-14% moderate erosion 0.37 B IIIe 30 Nicollet 1-3% 0.24 B I 20 Webster 0-2% 0.24 B Iiw 56 Clarion 2-5% 0.28 B Iie 70 138C2 Clarion 5-9% moderate erosion 0.28 B IIIe 30 Spillville/Coland 0-2% 0.28 B/D Vw 5 Totals 211 Use mid-point of slope class for slope and assume 200 ft hillslope lengths for all C = corn after beans, chisel-disk-till with 30% cover after planting P = 1 no erosion - practices being applied Excel Sheet on back of lab: Use data on handout to fill in blanks use math calculations in excel to make the calculations. Mapping Unit R K L feet S % L/S LS Table C P A tons/acre Area for unit - ac Total A tons/unit Delivery Ratio Delivered sediment Present Condition Use Excel table at the back of lab to calculate A for 4 scenarios 1. Present conditions what we have been talking about until now 2. 62D2 (Storden) all put in CRP planted to grass same C for the rest 3. All slopes > 3% terraced now P has a value same C for all 4. If all was in native prairie C Use Table 15-4 no appreciable canopy grass cover 62D2 138C2 Totals Scenario 2 Storden (62D2) all planted to prairie instead of cropped. Scenario 3 All slopes >3% are terraced use specific P value. Scenario 4 Whole watershed planted to prairie. USLE A = tons of soil/year moving on the site but not necessarily getting to Bear Creek via the gullies on the site A = Tons of Soil Moved Not Soil Delivered to Channel Use Erosion and Delivery Protocol ( Tools Handout) to determine delivery to channel page 8 Need to calculate Delivery using Delivery Ratio (SDR) Calculate from Erosion and Delivery Handout 1. Use Chart I page 8 Farm is on the Des Moines Lobe size is 211 ac/640 ac mi -2 = 0.3 mi 2 2. Adjust SDR using modifiers on page 9 3. Multiply adjusted SDR by Total A = tons of delivered sediment to Bear Creek 4
Watershed 2 as long as wide = +2 Delivery Ratio Modifiers Page 9 Gully watershed is 211 acres in size = 211 ac/640 ac sq mi = 0.33 sq mi 8.2% 2 D 2 About 62E 2 2as long as wide Why does that increase sediment delivery to Bear Creek? Nicollet 62E 2 Storden 62D 2 Spillville Clarion Coland Webster Watershed 2 as long as wide = 2 1/3 A, B, (C+D) slopes Rolling = -1 Delivery Ratio Modifiers Page 9 138C2 0-50 ft = -2 62D 2 Hanson Gully Soils Map Watershed 2 as long as wide = 2 Delivery Ratio Modifiers Page 9 Rolling = -1 Integrated (connected) Drainage Pattern 0-50 ft = -2 Incised = 2 Integrated = 1 Hanson Gully Watershed 5
Watershed 2 as long as wide = +2 Delivery Ratio Modifiers Page 9 Excel Sheet on back of lab: Use data on handout to fill in blanks use math calculations in excel to make the calculations. Mapping Unit R K Present Condition 62D2 L feet S % L/S LS Table C P A tons/acre Area for unit - ac Total A tons/unit Delivery Ratio Delivered sediment Rolling = -1 0-50 ft = -2 Add 2% to value from Chart I page 8 Erosion and Delivery Handout 138C2 Totals Scenario 2 Storden (62D2) all planted to prairie instead of cropped. Scenario 3 All slopes >3% are terraced use specific P value. Scenario 4 Whole watershed planted to prairie. Incised = +2 8.2 + 2 = 10.2% Integrated = 1 Gully Erosion Estimation Ephemeral Gully Estimation Next estimate sediment contribution from ephemeral gullies For each 20 ft section use mean of the top and bottom widths for width & mean of depths for section depth. Gully Erosion Estimation 20 ft 6
What do we have to know to determine amount of bank erosion? Eroding length Bank height Widening rate Soil density Channel Response to Changing Watershed Hydrology Need Volume of Soil Lost & Density Length Widening Rate Height Density 90 lbs/ft 3 Bank Erosion Categories Based on 2/3 of the Vertical Bank Fitting Criteria Page 5 Erosion and Delivery Very Severe 0.5 ft/yr Severe 0.4 ft/yr Soil Density = 90 lbs/ft 3 /2000 lbs/ton 350 ft long Ave Height = 6 ft Very Severe 25% Severe 50% Length is Channel Length Bank Length is 2 That 700 ft of bank VS = 700 0.7 = 490 ft 7.7 ft = 3,773 ft 2 0.5 ft/yr = 1,886.5 ft 3 90 lbs/ft 3 /2000 lbs/ton = 84.9 tons/yr S = 700 ft 0.3 = 210 ft 7.7 ft = 1617 ft 2 0.4 ft/yr = 646.8 ft 3 90 lbs/ft 3 /2000 lbs/ton = 29.1 tons/yr 350 ft Channel length Ave Height = 7.7 ft Very Severe 70% Severe 30% 350 ft long Ave Height = 6.5 ft Very Severe 40% Severe 50% N Delivery Rate for Concentrated Flow Erosion Integrated Drainage System Incised Channel Ephemeral Gully 50-90% Classic Gully 80-100% Stream Bank 80-100% We will use 90% for this Classic Gully Use Excel Table LgHansonGullySoilLoss 7
Very Severe (VS) 0.5 ft/yr Severe (S) 0.4 ft/yr NE = Not eroded Total Bank Erosion for Gully = 257.4 tons * 0.9 (SDR) = 231.7 tons A standard 16 cy dump truck (~20 tons) = about 11.5 trucks 1 ac furrow slice 1000 tons; 1 inch = 167 tons = 1.4 in from 1 ac 700 ft bank, 6 ft hight 25% VS, 50% S, 25% NE Very Severe 23.6 tons Severe 37.8 tons 700 ft of total bank, 7.7 ft high 70% of that VS & 30% S Very Severe = 84.9 tons Severe 29.1 tons 700 ft total bank, 6.5 ft high 40% VS; 50% S erosion, 10% NE Very Severe 41 tons Severe 41 tons N Delivered Gully Erosion = 273 tons Sheet & Rill Erosion = 266 tons Total 539 tons or 27 semis full Or 3.2 inches from 1 acre Hanson Gully Topo Map One team on either side Keep track of total length Location of each eroded bank Height, Length & widening rate (ft) Groups 1 & 2 Groups 3 & 4 Use the same techniques as we did for the classic gully to estimate sediment from Bear Creek stream bank erosion. Groups 5 & 6 Groups 8 & 9 Also calculate the % of bank length that is eroding in this reach of Bear Creek Groups 7 & 10 Groups 11 & 12 Also calculate % of total banks that are severely eroding. Use HansonStmBnkLoss Excel Table to calculate Bank erosion is a natural phenomenon part of channel dynamics. Healthy streams have 20% or less of their banks eroding. Groups 7 & 10 Groups 11 & 12 8