The improved monitoring device includes a data acquisition device with an accelerometer inside a bendable tube. One end of the tube is connected to a pole that may be secured to the top of a sewer manhole, while the other end is submerged in a fluid flow. The tilt, oscillations, and pressure exerted upon the tube due to fluid flow are measured and recorded. An improved method includes installing several monitoring devices into sewer system manholes, recording fluid level and flow, reading the recorded data, and displaying the data in chart or map form. Data may be displayed in two or three dimensional maps that may be overlaid with information of topography, street maps, and single or multiple sewer systems. Data displayed on the maps may include fluid flow rates, fluid levels, derivatives and integrals of flow rates, and differences in fluid levels or flow between monitoring devices.