Manoa Watershed Runoff

By: Mari Doi, Travis Voeller, Kiku Mochimaru, Victor Lee, Boyd Mackenzie, Rebecca Mierzejewski, Daniel Mehrez, Will Couture

Objectives

Calculate runoff for Manoa watershed (60 grids) using Curve # Method and base flow

RO-the amount of precipitation that is unavailable for groundwater recharge

Model Runoff using the Curve Number Method

•Each grid assigned a CN number based on the dominant current land cover.

•Soil properties and hydrologic condition were taken into consideration.

Grid

Land Cover Level I Land Cover Level II

% Land Cover Level II

CN Value II

CN Value I

CN Value III

1 3 Rangeland32 Shrub and Brush Rangeland 100% 86 71 95

2 4 Forest Land 42 Evergreen Forest land 1% 83 67 93

2 3 Rangeland32 Shrub and Brush Rangeland 99% 79 62 90

3 3 Rangeland32 Shrub and Brush Rangeland 100% 79 62 90

4 4 Forest Land 42 Evergreen Forest land 100% 77 59.5 89.5

5 4 Forest Land 42 Evergreen Forest land 100% 77 59.5 89.5

6 4 Forest Land 42 Evergreen Forest land 100% 77 59.5 89.5

7 4 Forest Land 42 Evergreen Forest land 25% 77 59.5 89.5

7 3 Rangeland32 Shrub and Brush Rangeland 75% 79 62 90

8 3 Rangeland32 Shrub and Brush Rangeland 100% 79 62 90

9 3 Rangeland32 Shrub and Brush Rangeland 100% 79 62 90

10 4 Forest Land 42 Evergreen Forest land 100% 77 59.5 89.5

11 4 Forest Land 42 Evergreen Forest land 100% 60 40 78

12 4 Forest Land 42 Evergreen Forest land 100% 60 40 78

13 4 Forest Land 42 Evergreen Forest land 89% 60 40 78

13 3 Rangeland32 Shrub and Brush Rangeland 11% 69 50 84

14 4 Forest Land 42 Evergreen Forest land 49% 66 46 83

14 3 Rangeland32 Shrub and Brush Rangeland 51% 69 50 84

Model Runoff

CN for Antecedent Moisture conditions (I & III) assigned.

ROMatrix program used to determine model runoff for each grid using:

-CN-Actual Rainfall

Total Runoff (mm)

1

2 3   0-100mm

4 5 6 7 8 9   100-200mm

10 11 12 13 14 15 16   200-300mm

17 18 19 20 21 22 23   300-400mm

24 25 26 27 28 29   400-500mm

30 31 32 33 34 35   500-600mm

36 37 38 39 40 41

42 43 44 45 46 47  

48 49 50 51

52 53 54

55 56 57

58 59

60

Use ROMatrix.exe to find estimated runoff for each grid cell

Calculate estimated stream flow

Find the average runoff of all 60 grid squares for each day

Multiply by area of the watershed to get volume of discharge

USGS 16242500 Manoa Str at Kanewai Field, Honolulu, Oahu, HIStream Discharge Datahttp:/ / nwis.waterdata.usgs.gov/ nwis/ nwisman/ ?site_ no=16242500&agency_ cd=USGS

Discharge, Discharge,

date ft3/ s m3/ sMeasured (cu

m per day)8/29/2010 18 0.509703239 440388/30/2010 5.6 0.158574341 137018/31/2010 5.1 0.144415918 124789/1/2010 5.9 0.167069395 144359/2/2010 8 0.226534773 195739/3/2010 8.3 0.235029827 203079/4/2010 5.2 0.147247602 127229/5/2010 4.8 0.135920864 117449/6/2010 5.7 0.161406026 139459/7/2010 24 0.679604318 587189/8/2010 6.8 0.192554557 166379/9/2010 5.1 0.144415918 124789/10/2010 8.4 0.237861511 20551

Determining Baseflow•Look at the average minimum stream flow on days with no rainfall•From the runoff found from ROmatrix, get average and multiply it by the area of the watershed to get volume of runoff•Look at difference of the measured and modeled stormflow

Adjust curve numbers to optimize runoff estimates

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

8/20/2010 8/30/2010 9/9/2010 9/19/2010 9/29/2010 10/9/2010 10/19/2010 10/29/2010 11/8/2010 11/18/2010 11/28/2010

Measured (cu m per day)

Model stormflow plusBaseflow

Calculate weighted base flow

o Find average rainfall for each grido Find average rainfall for all gridso Base flow for grid= (average rainfall

per grid)/ (average rainfall for all grids * average base flow)

% Runoff from Total Precipitation

% Runoff from Precipitation

Total Rainfall vs. Total Runoff

Conclusion

Adjusted curve #’s & added base flow provided us with the most efficient results of basin RO

RO results can then be plugged into water balance equation as an output of water

Runoff was calculated by obtaining precipitation data and utilizing the curve number method. By adjusting the curve numbers and adding base flow, the data was a close representation the model data from the USGS results.