Flow to horizontal drains in isotropic unconfined aquifers

The Laplace-transform solution for the problem of flow to horizontal drains in an anisotropic unconfined aquifer is derived. The solution for the constant flux horizontal- well by Zhan and Zlotnik [Zhan, H., Zlotnik, V.A., 2002. Groundwater flow to a horizontal and slanted well in an unconfined aquifer. Water Resour. Res. 38(7), 13-1-13-11.] is modified to obtain the solution for a constant head horizontal drain. The Laplace-transform solution is converted to the real time domain, and type curves for the drawdown around and the discharge to a horizontal drain are computed. The solution is verified by a numerical simulation. The type curves and derivative type curves of the drains are compared with type curves for horizontal wells. The sensitivity of type curves on piezometer location, specific storage, horizontal drain elevation, aquifer delay index and drain length is tested. These type curves can be used for interpretation of drainage data.