1 Copyright 2019 | Philippine Engineering Journal Phil. Eng’g J. 2019; 40(2): 1-14 R. MACUHA Estimating the Yield of a Collector Well with Parallel Infiltration Galleries as Laterals Richmark N. Macuha Institute of Civil Engineering, College of Engineering University of the Philippines-Diliman, Philippines Abstract – In recent years, collector well with horizontal laterals is being used more often to tap groundwater resources. However, at the moment, majority if not all yield studies are focused on collector wells with radial orientation of laterals. In countries where trenchless technology is still uncommon, like in the Philippines, collector wells either have a single long lateral or parallel laterals. This paper presents applicable yield estimation techniques for collector wells with parallel laterals in the riverbed. The first method uses a source-sink pair model and image well theory, obtaining an approximate analytical solution. The second makes use of MODFLOW, a numerical approach to come up with a local groundwater model. The estimates from both are found to be in good agreement with actual yields measured in a study area. The developed equations can be used for rapid estimation of yield to other candidate sites. Although the MODFLOW model produced more accurate results than the approximate analytical method, it should also be used with caution as the estimates are usually greater than the actual, which can pose a problem for water supply development. Keywords—collector well, infiltration gallery, horizontal well, water supply I. INTRODUCTION In recent years, collector well with horizontal laterals is being used more often to tap groundwater resources. This well can produce higher yield under the same drawdown level [1] and has less risk of saltwater intrusion in coastal areas [2] as compared to a conventional vertical well. It can also extract water from shallow but highly permeable aquifers [3]. For collector wells with laterals at or near riverbeds, well operation triggers riverbank filtration process which significantly improve the quality of pumped water in terms of turbidity and contaminant concentration [4, 5]. The amount of water that can be extracted, or the yield, is one the most important considerations for any water supply intake. For collector wells, several yield estimation methods had been developed through the years. One of the earliest ways is to assume that the whole assembly is equivalent to a hypothetical vertical well with effective radius that must be solved empirically [6]. Hantush and Papadopoulos [7] first described analytically the head and flow distribution around radial collector wells using boundary-value analysis in line-sink elements. The same general concept was used by Analytic Element Method (AEM) to represent horizontal wells [3, 8, 9]. Liongson [10, 11] provided a simple approach to develop a 2-dimensional steady-state flow equation of a single horizontal well using a source-sink pair under constant head. By direct use of analytic geometry of circles and algebraic manipulation of potential function, he obtained the same results as Kolymbas and Wagner [12]. PHILIPPINE ENGINEERING JOURNAL PEJ 2019; Vol. 40, No. 2: 1-14