You could use an inline UV system with the pump but the flow is pretty high so you'd need a pretty reobust UV system especially for the size of the pond. Usually the UV systm would have recommended flow rates so if yours can handle 113 gallons per minute it would be fine.
Another option would be to use the larger size up and split the line and have one section going to the inline UV unit and the main flow could be sent direct to the waterfall.
With an unlined pond that size I'm not sure a UV filter would be financially worthwhile. Most of the UV systems I know are for much smaller ponds than the 90,000 or so gallons your pond has.
A UV filter for a 15,000 gallon pond can run $1000. You'd need 6 UV filters at that rate!
Since you have a natural pond, and natural ponds are what our company deals in mainly, I would recommend adding a safe and natural bacteria to ensure algae free conditions. We have koi and fish safe liquid blends that give fantastic results and the cost will be much less than operating mechanical filtration with UV.
The liquid bacteria are added every one or two weeks and are safe for all fish, plants, pets and people.
Not sure if you have skimmers or are planning on using a filter falls type waterfall but in our natural ponds the bacteria with proper circulation and aeration you can keep things really crystal clear by using the beneficial bacteria especially with a simple bio-filter set-up or even without.
If you want to go with the external pump EXP-SF-6781 pump would enable you to have a good flow on a 36" to 48" width at that height. This external pump will give you a very good flow even at that height and even if you use a long tubing run.
More can be found here: http://www.thepondreport.com/pond-pumps.shtml