Coal ash is one of the largest industrial waste products generated in the United States. Coal ash is commonly stored as a slurry form in impoundments. Due to new Environmental Protection Agency (EPA) regulation of coal ash disposal, coal ash slurry must be dewatered to dispose of the ash safely. Geotextile tube dewatering is an important and sustainable method of dewatering coal ash slurry. There are multiple testing methods that are used to evaluate the dewatering performance of geotextiles. These tests can range from a one-dimensional Pressure Filtration Test (PFT) to a pressurized two-dimensional test (P2DT). The P2DT test setup simulates a cylindrical geotextile tube, where axial and radial flows can be measured and collected separately. Since, 1-D is a common small-scale test for researchers, a comparative study has been carried out to evaluate the difference in flow rate, filter cake properties and turbidity of filtrate in 1-D vs. 2-D dewatering tests. For this purpose, one monofilament/fibrillated tape yarn woven geotextile and one composite geotextiles were used, and 10% solid content was used with conditioned and unconditioned fly ash in both 1-D and 2-D tests. Based on the results it was found that the dewatering behavior of both geotextiles were almost similar in 1-D test. In 2-D test, a variation in dewatering rate and quality of the filtrate were noticed for both geotextiles, which represents the dewatering behavior of a geotextile tube. However, the average solid content of the filter cake for both tests was in similar range.