While you may get some top-kill, vinegar will not control the majority of the weeds in your situation since it does not travel to the roots of the weeds. Also understand also that highly concentrated vinegars are much more toxic and much more dangerous to the applicator than the Roundup you might use in the same situation. Roundup will also be less expensive, as long as you purchase the concentrated product and dilute it yourself. Your recipe of vinegar and salt is much more likely to be environmentally damaging, especially used near drainages and creeks.

Here is a link that might be useful: Purdue link

Salt can sterlize the soil. Not a pretty sight and not to be used for killing vegetation with or without vinegar. Definately not along creeks either.
Realistically, if you wanted to kill everything along this creek you would probably need 15-20ish ounces of roundup concentrate to do the entire job and definately less than a quart of product.
Personally I would start with the brambles and broadleaf weeds first using products that are more specific to them.
Why are you trying to eliminate all the grasses as well?

Thanks for the input. The reason that I want to get rid of the grass too is that the area is not suited for lawn / grass. I intend to get rid of everything and then plant some shrubs, trees etc in the spring and cover the area with a thick mulch so the problem does not happen again overnight. I moved into this house about a year ago, and this is one area I have not attacked yet.

I think that I may end up using some crossbow - sounds like it is really strong and should kill most all of it.

Crossbow is 2,4-d and triclopyr and is an effective control for broadleaf brush and woody plants, but it is specific for broadleaf plants only. It will not kill the grass at your site. You will need to use an additional herbicide that affects all weeds, such as Roundup if you want to control all of your weeds. It's also important to know that Crossbow can be volatile in warm weather, so follow the label directions closely.

Roundup is expensive, but it's no better or worse than any other glyphosate based weedkiller in my experience. I mix generic stuff from concentrate at a fraction of the cost.

However, while glyphosate is well suited for use on soil as it breaks down quickly and is not particularly persistent, it is far more toxic in the aquatic environment and can be persistent. I wouldn't go within several meters (at least) of the creek when applying it. Laying down weed mats or fabric of some type to smother the weeds may be preferable in this area.

Generally, when applying any weed killer near water you have to be more careful. Aquatic environments are far more sensitive to chemicals than soil, most garden products can damage them.

Actually, glyphosate is suited for use near water due to its very low toxicity to fish and aquatic organisms, in fact there are formulations that are legally labeled for use directly IN waster, although they lack the surfactant component that is toxic to fish, as all surfactants and soaps are. Even the general use Roundup products containing surfactants are legal to use near water, as long as no drift or overspray hits the water. They are often used to remove non-native invasive plants near streams and ponds in woodlands.

Unfortunately, new research is finding that glyphosphate is not safe as had been previously believed.

Here is a link that might be useful: New 2005 Roundup Findings

If you want to know the latest poop on Roundup, listen closely to JAYK. He's convinced me that he really does know more about it than anyone else I've seen on the GardenWeb forums.

I use vinegar at 20% acidity to spot kill some weeds in my turf. As JAYK said, vinegar is more hazardous to the applicator than RoundUp is. What he didn't say is what is more hazardous about it. The biggest danger is inhaling the fumes and burning your lungs. Fortunately God gave us noses to detect dangerous smells and fumes. The time it takes to burn your lungs is about 10 times longer than the time you can stand being anywhere close to the fumes. This vinegar is really strong smelling, so the fumes are not usually a problem. The second problem is splashing it in your eyes. IT WILL CAUSE BLINDNESS - at least temporarily, like for 3 months. So be very careful with it if you decide to use it. The next problem with vinegar is that it has a widely varied effectiveness. If you have oxalis, it will die, dry up, and disappear in 20 minutes. If you have English ivy, you can spray and spray and spray with no effect at all.

Having said all that encouraging stuff, you might be able to get 20% vinegar at Lowes. Call first and be sure you talk to someone in the garden chemicals area. If you have an organic garden center nearby, you might find it there. Since you have to use the vinegar at full strength it is not necessarily economical for large areas either.

On the positive side vinegar is a carbohydrate. It is used for weed control as a FOLIAR SPRAY, not a soil drench. Any overspray that hits the soil will be absorbed and becomes a food to the soil microbes. So there is no problem with the vinegar to the environment. Salt is a different story.

If I had your situation I would just mow it down with a rented mower or rented weed whacker.

JAYK gave an abstract by "Williams, Kroesb, Munroc". No date was given and no journal information was given.

The following Google Scholar link will take you to what is probably it (apparently he mispelled 2 of the authors' names - Kroes and Munro) . Please notice that it is a year 2000 publication.

http://scholar.google.com/scholar?hl=en&lr=&q=williams+kroes+munro+glyphosate&btnG=Search

Since it was published in 2000, it cannot tell you anything about more recent glyphosate health research. You can become familar with some of the more recent studies since Google Scholar "hits" include references to papers that cite the paper of interest. In this case there are 42 papers found. If you click on the "cited by 42" link, you can see what their abstracts say.

Here is a link that might be useful: See the first hit at this link