Personally I would convert the text files to dBase or better still a GeoDatabase Table as then your data is in a Table which will make joining easier.
// Create a text file workspace factory.
Type factoryType = Type.GetTypeFromProgID(
IWorkspaceFactory workspaceFactory = (IWorkspaceFactory)Activator.CreateInstance
// Open a directory of CSV files using its path.
IWorkspace workspace = workspaceFactory.OpenFromFile(@"C:\Data\CSV", 0);
// Open a CSV file as a table.
IFeatureWorkspace featureWorkspace = (IFeatureWorkspace)workspace;
ITable table = featureWorkspace.OpenTable("Levee.csv");