You might be able to sue, if (1) it was negligent to either not finish the ditch or, if not going to finish it, to not block or mark it off in some fashion; and (2) the city had notice, or knowledge, of the condition. If it was a municipal project, then (2) would seem to be met; and as for (1), negligence means more careless than the hypothetical reasonable person--e.g. a reasonable person would have done something differently.Note that is usually a short time frame to file a claim against a city (or state, or government agency) and strict paperwork requirements to comply with in order to do so. If you are interested in pursuing this further, you should speak with an attorney about the matter *immediately*.