A neighbor passed along this US Department of the Interior document from 1977 titled “Washington DC’s Vanishing Springs and Waterways.”
I have not read this document, but notice on page 7 a rough map of DC’s “downtown areas’s original streams.”
Plus there is a looong description of the Tiber Creek.
In consideration of the recent neighborhood flooding — and not just in Bloomingdale! — I thought that Bates area residents might like to see where the Tiber Creek flowed.
Bates Area Civic Association 
The link tells me that I need to set up an “A Drive” account to download this file. Is there another way to get it?
I heard that DC was built overtop swamp land.
Guess it might be true.
Bing suggests that the entier document is Washington DC’s Vanishing Springs and Waterways. 1977. USGS circular 752. I cannot find a link just yet. Only another reference. However, it looks like North Capital Street was first Tiber Creek.