Collect rainwater from culvert

On our property we have a culvert that runs under a dirt road. When it rains, water spills down the dirt road, into the culvert, and splashes down the hillside into a seasonal streambed.

When it rains, a lot of water flows from the culvert. I would like to collect this water. Making a pond would be great, but I don't have that kind of machinery available right now. In the future I would love to make a pond.

Any ideas for attaching some sort of gutter to tap into the culvert, routing the water into a large storage tank?

There's a lot of sediment (dirt) from the road in the fast-flowing water.

Should I be concerned about anything (cadmium?) from tires, since it is a road?

Any good trick for filtering the sediment before it runs into the tank?

Stephen - hiring an excavator will be a LOT cheaper then constructing an appropriately sized tank. If all you want is to delay the water so it has a chance to infiltrate and rehydrate your soils you wouldn't necessarily need to even seal the pond. I recently was talking to someone who hired a digger (not sure what size) for a week to make a pond. They did all the driving themselves and paid just £300. They went on to seal it with bentonite clay, which worked out cheaper than a pond liner.

Alternatively you could dig some on-contour swales and channel the water into these, so that it overflows from one into the next and on down the hillside.

Im not sure if what Im doing is going to work, so it for what its worth.

I just rented an excavator just outside washington, dc for 200$ a day, 150$ delivery. We needed it to fix our main water line that busted in the middle of a field. I kept the machine for an extra day and dug my pond, and rainwater catchment system, really easily. Its a wonderful machine and not too hard to get the hang of. I learned how to use it the first day digging the hole for the water line, so maybe it could take an extra day or so if you have more digging or no experience. My pond is 27x12x4 with steps. There is 100' of trench that I dug with the machine that feeds the pond, including 5x10x2 reed bed in line with the trench. Most of the time was spent on grading of the earth. Special care must be made to separate top soil, clay, rocky soils if you got em. Not sure if i need to line it yet. I have alot of clay but also rocks.

I more or less constructed the trench as a swale (berm on lower slope) but I believe it needs to be a diversion drain. As I understand it, Mollison describes a swale as only trying to stop the flow and control the water infiltration (usually on contour). A diversion drain transports the water. For this reason, im de-emphasizing the berm so as not suck moisture from the drain. More importantly, Im moving towards a drain liner and gravel to limit the infiltration of the water while in the drain. Im also considering using found materials in the drain (streambed) like tin roofing in thin strips.

I plan on using broom sedge, a native grass weed as my reed to filter and purify the water in addition to stabilizing soil from erosion. Its a noted and despised weed amongst farmers, so I get a kick out of trying to use it for benefit. It may have allelopathic properties but that sounds more like it being suited for extreme conditions (poorly drained acidic soil).

Any updates?

one more thing, theres a picture in mollison's manual about catchment of heavy metals as they flow down through stepped beds. Indivual beds are sloped back towards the slope, like they are swales. Metals collect in this ridges, if you will, while water flow over and down the steps. I believe this technique was tailored more for the harvest of metals, but I would imagine it would be a help in purification. flow forms are awesome but expensive so i may try making one from a mold using concrete.

Is anything sprayed on the road to reduce dust? Do you want this in your catchment? Do they spray salt brine or use road salt? I've heard it not uncommon for people to dump undesirables on the road like draining their RV septic tank or dumping waste oil instead of paying to dispose of it properly.