Distance markers are used to match WEAP and QUAL2K reaches, as well as point and diffuse inflows and outflows. You must be careful that the locations in the .q2k file (entered on the "Reach" worksheet in QUAL2K) match the distance markers entered in WEAP, especially for tributary inflow points. However, the reach boundaries in QUAL2K do not need to match the reach boundaries in WEAP, because point and diffuse source data are entered according to locations, not reaches.
Each QUAL2K reach is subdivided into 1 or more equal-length computational elements. Results are calculated for each element. When WEAP is reading the QUAL2K results, it must find the closest matching QUAL2K computational element for each WEAP node and reach. For nodes, WEAP chooses the closest computational element at or downstream of the node. For reaches, WEAP chooses the closest element to the middle of the WEAP reach, as long as it isn't upstream of the reaches upstream boundary.