Little River Watershed Conservation Practice Assessment with SWAT. D.D. Bosch, J. Cho, G. Vellidis, R. Lowrance, T. Strickland

Transcription

1 Little River Watershed Conservation Practice Assessment with SWAT D.D. Bosch, J. Cho, G. Vellidis, R. Lowrance, T. Strickland

2 Outline Background Impacts of riparian forest buffer (RFB) Allocating Best Management Practices Results and Summary

3 Background Little River Experimental Watershed in CEAP

4 Little River Watershed 8 stream gages (334 km 2 ) Low slope, 2-3% Dense stream network 41% row crop agriculture, 47% forest Channels bordered by riparian forest

5 Objectives Evaluate impacts of riparian forest buffers (RFBs) and conservation practices (crop and nutrient management) Evaluate most effective approach for allocating Best Management Practices

6 Modeling procedure Cause: land management changes Effects: Changes in Hydrology and WQ

7 Calibration and Validation Calibration on LRK Period: Rotation: Cotton-Cotton- Peanut Validation on LRB without changing parameters 17 km km 2

8 Calibration and validation - LRK LRB for Criteria Streamflow (mm/yr) Sediment (ton/yr) TN (kg/yr) TP (kg/ha/yr) Cal. Val. Cal. Val. Cal. Val. Cal. Val. Observed/Simulated 326/ / / / / / / /7764 % error Monthly NSE Calibration Monthly TN yield (kg) Monthly streamflow (mm) 200 Observed Simulated Streamflow 4500 Observed 4000 Simulated Total Nitrogen (TN) Monthly TP yield (kg) Monthly sediment yield (ton) 300 Observed 250 Simulated sediment Total Phosphorus (TP) Observed Simulated

9 14 m variable filter width for current conditions - width determined by current extent of buffer 14 m constant filter width for maximum conditions

10 Impacts of riparian forest buffer - Extent Representing -No buffers -Existing buffer conditions -Maximum buffer conditions

11 Load Reductions due to Riparian Buffers - Extent Sediment Load (ton/ha) % 21 % Total N Load (kg/ha) % Total P Load (kg/ha) % 0 No RFBs Current Buffers Maximum Buffers 0 No RFBs Current Buffers Maximum Buffers 0 No RFBs Current Buffers Maximum Buffers Sediment Nitrogen Phosphorous

12 Impacts of riparian forest buffer - Location Stream-order approach: starting from low stream order to high stream order, applied buffers to all un-buffered area 1 st order > 2 nd order > 3 rd order > 4 th order > 5 th order 72% 87% 95% 99% 100%

13 Impacts of riparian forest buffer - Location Sediment load from HRU to stream (ton/ha) % 21.7 % Current RFB Maximum RFB 3.8 % 1.0 % 0.1 % Reduction rate (%) Sediment Total nitrogen Total phosphorus 0 1st 2nd 3rd 4th 5th Stream order 0 1st 2nd 3rd 4th 5th Stream order Sediment Reduction rates

14 Results - Buffers Maximizing buffer extent could be expected to produce minor decreases in sediment (21%), total N (7%), and total P (20%) of the HRU load, less at watershed outlet Greatest impacts on would be obtained by installing buffers on lower order streams, higher order streams already buffered Greatest impact on sediment followed by phosphorous followed by nitrogen

15 BMP allocation approaches - Major Conservation Practices Crop management practice (CMP) Contour farming, grassed waterway, terrace, and conservation tillage, are grouped together Nutrient management practice (NMP) 30 % decrease in nutrients applied

16 BMP allocation approaches Random approach: represents current allocating method 16% 33% 50% 76% 83% 100% of remaining crop areas Stream-order approach: starting from low stream order to high stream order 36% 72% 87% 95% 99% 100% 1 st order 2 nd 3 rd 4 th 5 th NMP Modeling approach: BMPs applied to critical areas based upon SWAT HRU output (Targeting) 16% 33% 50% 76% 83% 100%

17 Load Reductions due to Crop Management Practices - Extent % 4.0 Sediment Load (ton/ha) % Total N Load (kg/ha) Total P Load (kg/ha) % 0.0 Current Maximum 0 Current Maxiumum 0.0 Current Maximum Sediment Nitrogen Phosphorous

18 Load Reductions due to Crop Management Practices Extent and Location Sediment Total phosphorus (TP)

19 Load Reductions due to Nutrient Management Practices - Extent Sediment Load (ton/ha) % Total N Load (kg/ha) % Total P Load (kg/ha) % 0.0 Current Maximum 0 Current Maxiumum 0.0 Current Maximum Sediment Nitrogen Phosphorous

20 Load Reductions due to Nutrient Management Practices Extent and Location Total nitrogen (TN) Total phosphorus (TP)

21 Results BMP allocation Comparison of implementing Riparian forest buffers RFB, crop management plans (CMP), and nutrient management plans (NMP). Sediment: CMP > RFB > NMP Total nitrogen: NMP > RFB > CMP Total phosphorus: CMP > RFB > NMP Impacts of spatial allocation approaches Targeting most critical areas showed the greatest reduction rates

22 Conclusions Model application indicates the greatest environmental gains can be obtained through targeting critical areas Buffers should be installed / retained on all lower order streams Greatest impact is expected through maintaining existing buffer systems Substantial investment would be necessary to see incremental changes in nutrient loading

23 Questions?