The DCA river approach is easy.
Start outside the DCA dme (111.0) and cross the 10 dme at 3,000ft over the river. Start your decent there. Multiply the dme x 3 and that will be the desired altitude all the way down. Be sure to stay over the river all the time. There is a quick jog to the left and then the right at 500ft to remain over the water. Don't miss that or you might get a phone call from your chief pilot who had a call from the FAA. Maybe not, but the people on the ground appreciate it. Besides, It's a fun approach.
















Start outside the 10 dme of DCA vor over the river and cross the 10 dme at 3,000 ft.
Multiply the dme distance times 3 all the way down and it will work just right.