CEEn-531 Dr. Nelson
HMS Results
Comparison from the curve number sensitivity
Curve Number Sensitivity
| Condition | Curve Number | Initial_Abstraction | Peak Flow |
| CN Normal | 67.6 | 0.958 | 173.40 CFS |
| CN Wet | 83.56 | 0.393 | 743.20 CFS |
| CN Dry | 48.12 | 2.156 | 10 CFS |
You should have noticed that the shape is the same, but the volume and peak increase with increased CN, and that the result is in fact quite sensitive.
Comparison from Initial abstraction sensitivity
Initial Abstraction Sensitivity
| Condition | Curve Number | Initial_Abstraction | Peak Flow |
| Ia = 0 | 67.6 | 0 | 572.5 CFS |
| Ia = 0.1S | 67.6 | 0.479 | 363.20 CFS |
| Ia = 0.2S | 67.6 | 0.958 | 173.40 CFS |
You should have noticed a significant difference in the runoff for the different Initial Abstraction ratios.
Comparison from soil type sensitivity
| Condition | Curve Number | Initial_Abstraction | Peak Flow |
| SSURGO | 67.6 | 0.958 | 173.40 CFS |
| STATSGO | 68.7 | 0.911 | 195.60 CFS |
You should have noticed that there is a slight different in the CN value when using the STATSGO (more B) than SSURGO
Comparison from the SCS, Initial and Constant Rate, and Green and Ampt methods
Initial and Constant Rate Method
|
Condition |
Initial Loss |
Constant Rate |
Peak Flow |
| Single Basin | 0.2 | 0.85 | 280.30 CFS |
Green and Ampt
| Condition | Initial Loss | Moisture_Deficit | Suction | Conductivity | Peak Flow |
| Single Basin | 0.2 | 0.2 | 12 | 0.25 | 214.6CFS |
I was quite surprised really by the difference in shape of the SCS method and want to go back and check this if I have a chance to make sure the same unit hydrograph was used for all three.
Comparison from spatial variation sensitivity using the SCS method as a single basin, two basins, and with MODClark
Similar results, but it would appear that the more you average CN, the less runoff there is. This actually corroborates a separate study that Murari and I have been performing.
GSSHA Results
Compare no infiltration with infiltration as defined in part 1.
No infiltration
| Condition | Manning's n |
|
No Infiltration, Uniform roughness |
0.15 |
Green and Ampt Redistributed with uniform infiltration
| Condition | Roughness | Hydraulic Conductivity | Capillary Head | Porosity | Pore distribution index | Residual saturation | Field capacity | Initial moisture | Peak Flow |
| GAR | 0.15 | 0.45 | 12 | 0.35 | 0.1 | 0.02 | 0.1 | 0.2 | 244.12 CFS |
No surprise here that considering infiltration makes a big difference.
Compare uniform infiltration with spatial distribution of infiltration parameters.
Spatially defined GAR parameters
| Condition | Hydraulic Conductivity (cm/hr) | Capillary Head (cm) | Porosity | Pore distribution index | Residual saturation | Field capacity | Initial Moisture |
| ID # 1 | 0.45 | 12 | 0.35 | 0.1 | 0.02 | 0.1 | 0.2 |
| ID #2 | 0.3 | 10 | 0.3 | 0.1 | 0.02 | 0.1 | 0.2 |
With spatial infiltration, and soils less pervious than the predominant B type we see more runoff and a higher peak.
Analyze the sensitivity of the different GAR parameters from 2b.
Larger K, porosity, and capillary suction produces less runoff.
I think the red hydrograph is offset just in the plot (not in reality). It's peak should be lined up with the others but was misplotted.
Compare GA method in HMS with GAR method in 1 and 2. Try to compare based on the relevancy with HMS modeling.
Very similar runoff volumes if you took time to compare. The different hydrograph shapes are a result of different runoff transformation methods which we will experiment in the next assignment.
Compare how HMS and GSSHA treat impervious areas.
HMS treats all impervious areas as directly connected, so it would make sense that it has more volume and higher peak than GSSHA, where runoff from impervious areas may move to cells that are pervious and experience losses through infiltration.
Any other important aspects/scenario that you might have observed.
I do not expect your results to be identical to these because you will undoubtedly have picked some different parameter values. You may even have some results that contradict what we did, but in general you should observe similar trends.
A couple of important things we noted as we did this.
1) We did not model initial abstractions in GSSHA, whereas for HMS you were probably entering an Ia = .75-1 inch based on your computed CN. This could have resulted in a rather large difference between GSSHA and HMS. When we ran HMS to compare to GSSHA we set Ia=0 and the volume comparisons were very close. GSSHA does have some options (interception, retention depth) that could model Ia, but we need more information and practice with them to better compare.
2) You may have noticed some different ranges of values for "wetting front suction" in the HMS reference and "capillary head" in the GSSHA reference. The values do not compare very well, with HMS values being generally larger than GSSHA. It would appear that while these parameters essentially represent the same physical property, but in order to see a good agreement between GSSHA and HMS we did not use identical values, but rather in HMS we used the recommended wetting front suction values and in GSSHA the recommended values for capillary head.