Future Flow conditions

[jdeebaba]

Hi I am trying to do some worst case scenario for flow. The rivers I am looking at are in Alabama. Is there any way to roughly predict the future flow conditions ? Suppose in 2050 I want to use the flow conditions affected by climate change. I believe flow is more or less related to precipitation. Would you suggest any ideas or reading related to future flow scenarios ? Thanks

Jdee

 

[MiketheEngineer]

How high is UP and how low is DOWN.

Predictions are truly difficult. Obviously the amount of rain will cause flow changes - but so will channel depth, path, sedimentation, etc.

Good luck

 

[GoldDredger]

Also keep in mind that future development will affect peaking factors on rivers. If a large area was previously open space, then becomes houses, roads and parking lots, the rainwater will 'travel' to the river much faster (unless local or regional detention ponds are used)

 

[jdeebaba]

Thank you MiketheEngineer and GoldDredger for your suggestions. But right now, I am not sure how to proceed to finding the future flow conditions. Any insight on how to proceed and what model to use for the future flow condition would be highly appreciated. Thank you.


Jdee

 

[CPENG78]

Hello jdeebaba,
Agree with both Mike and Gold...in following Golddredger's comment, I would look at both the master plans and zoning maps for the cities, towns that outfall into the river(s). This will give you an idea of where a city sees itself going into the future. You can extrapolate rainfall data but you would need to apply it based on the future growth in development. Historical maps that show changes in watershed would also help you determine any historical erosion of channel, sedimentation, etc such as the factors that MiketheEngineer mentioned.

Another route to go would be to assume that peak flows would be held back to historic flows once development is implemented. While a big assumption in some geographic areas, it has been the case in the smaller local projects that I work on.

 

[MiketheEngineer]

Also - look to the current laws for retention basins and "green spaces" being implemented in your area. Our county just started doing this about 20 years ago.

It basically boils down that you can only use a certain percentage of the plot for buildings, parking lots, tennis courts, pools, etc.

The retention basins have to be designed such that you are only allowed about a 10% increase of runoff - it varies around the area.

 

[fel3]

Assuming this all will end up in an engineering report of some sort, I suggest a section or two* in the report dedicated to how you made the predictions used for the analysis. Fully discuss the baseline data, the master plans consulted, the assumptions made, etc. Include maps and graphs.

* For a small report for a small area, you could combine current conditions and future conditions into one section. For a large report for a large area, I would definitely split the two.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[jdeebaba]

Actually, I want the flow for future conditions to use in the hydrodynamic model. I want to couple the effects of sea level rise and the flow conditions (future) and see the overall effect on the estuary. Actually I am not writing a report but I am trying to work on a paper. So, the most used method for predicting the flows is desirable. I have an option to use watershed models. But I don't know what watershed model should I use or simply use some correlation coefficient to address the flow change in future. Thank you all for your reply.

 

[beej67]

Land use changes due to urbanization are going to affect your flows MUCH MUCH MUCH more than "climate change" will.

I know urbanization isn't the sexy thing to research, because Goldman Sachs isn't dumping all sorts of money into "parking lot cap and trade," but it's your primary culprit for the environmental issue you're researching.

When you're talking about an estuary, basin urbanization will have two important effects. 1) the event flood flows (during/after storms) will be much higher. 2) the base flows (between storms) will be much lower. If you're working on a paper, and you're trying to dig up some stuff related to Alabama watersheds, do some research on the Apalachicola River and Apalachicola Bay. It's estuary has been majorly effected by urbanization in Atlanta and along the Chattahoochee/Flint, doing quite a bit of damage to what was once the most productive oyster fishery in the country. Where the water used to always be brackish, now it's either too salty between storms or too fresh after storms, because of how urbanization interferes with they hydrologic cycle. I'm sure quite a bit has been written about it, since it's a central element of the Southeastern Water Wars.

The first thing I'd do if I were you, is contact FEMA and pull the HEC-RAS model for the river you're working in, and ask them if they have a "future condition" model. The work may have already been done, at last for the 100 year storm. I know many municipalities will maintain multiple flood models, one for now and one for "future land use," based on their zoning plans and growth projections. Don't know if such a thing exists on a large scale though.

If you ultimately wanted to put together a 2050 hydrologic model of the whole basin and compare it to the current one, then that's a task of Masters Thesis complexity. You would need to create a hydrologic model of the entire basin based on 2050 land use mapping, and do some hydraulic analysis of it. The two obvious software packages to use would be HEC-HMS and HEC-RAS, but you might be able to do the whole thing in EPA-SWMM. Those being the free options, there's also plenty of $$ software that could do it.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[jgailla]

beej is spot on as usual.
However, it seems that you are looking for the change in rainfall/water level parameters over the next forty years, not change due to urbanization.
If this is true, just pick any number you want and find a report to match.
No one has any idea if there will be any difference in rainfall or sea level in forty years.
Probably sea level will be higher due to a warmer climate.
The "models" I've seen on the Internet range from one foot to fifty feet of rise or more, depending on what nonsense is input.