A Word About Drainage in Ocean City from the City Engineer
The Ocean City Engineering Department often receives inquiries regarding drainage problems within the City. With the above average rainfall we have received this spring, these complaints have increased substantially. While the Engineering and Public Works Department takes these concerns seriously and does our best to address them in a cost effective and timely manner, it is important to recognize some basic realities about drainage within Ocean City.
Ocean City is a barrier island. The land is only a few feet above sea level and extremely flat. Unlike some other barrier island resorts, which utilize open ditches to drain their road systems, Ocean City made a conscious decision in the past to utilize a system of curbed streets and sidewalks, with storm drain inlets connected to a system of underground pipes. These pipes, which rely on gravity flow only, then discharge the storm water into the bay.
The advantages of the type of storm water collection system used in Ocean City is that it allows for more efficient use of the road right-of-way (more area available for travel lanes, parking, and sidewalks), easier vehicle and pedestrian access from the roadway to adjacent properties and significantly reduces the amount of open stagnant water typically found is ditch systems. The disadvantage of such a system, particularly in flat terrain, is that runoff from the street is collected only at inlet locations, and not along the entire street length such as with a ditch system. Therefore any pavement settlement (and remember much of the Town was built on dredge spoil that settles significantly) which occurs away from a storm drain inlet results in standing water.
Sometimes eliminating standing water caused by street settlement is as easy as making a minor adjustment to the closest storm drain inlet. Often however, the only solutions to this problem are to either remove the pavement, repair and fill the failed soil beneath it and repave, or to install a new storm drain inlet and piping. Both are time consuming and costly. From 33rd street North, east of Coastal Highway, the problem is greater because there is no collection system east of the median on Coastal Highway. We rely purely on the surface slope of the street to carry water to the first inlets on the highway. Many times only major changes to the roadway itself will correct a drainage problem here.
The second challenge to drainage in Ocean City is the low elevation of the island. Most property in Ocean City is only a few feet above sea level. A typical street elevation in town is about 5 feet above mean LOW tide. What does this mean? Well consider a typical storm drain system, the first inlet is likely located on Coastal Highway more than 500 feet from the closest discharge point. The elevation of the highway is only 5 feet above a normal low tide, the top of the pipe must be buried at least 1 foot below the pavement level to prevent trucks from crushing it. The pipe should be at least 15 inches in diameter to prevent debris from clogging it. That means the bottom of the pipe must be no higher than 2.75 feet above an average low tide. Since we try to keep the bottom of the pipe at the outfall (where the pipe empties into the bay) no lower than the normal low tide elevation to insure at least some positive drainage at high tide (we’re not always successful), this means the average slope of our storm drain lines is less than 1% (1’ of drop for every 100’ of length).
The good old laws of physics for fluid in a pipe under gravity flow dictate that the capacity of the pipe is governed by three things: the size of the pipe, the slope of the pipe, and the “roughness” of the pipe. In addition, as tides at the pipe outfall increase and begin to submerge the outfall pipe, the capacity of the pipe to carry water is reduced, sometimes completely during extreme tides. If we use a larger pipe, the bottom is deeper in the ground and the slope becomes less. Since we currently use the “smoothest” pipe material available, the only way to increase the capacity of the storm drain system is to add more pipes or install a pump system. A pump arrangement is currently cost prohibitive for the number of storm drain systems we have here in Ocean City. Therefore, we have to balance the nuisance of occasionally flooded streets with the substantial costs of additional storm drain pipes. Now you know why Coastal Highway floods during heavy rains at high tide. Yes, it’s annoying and we are working to improve the situation but it takes time and lots of money.
Our final often heard drainage problem in Ocean City involves the development of a property adjacent to an existing home and subsequent standing water on the first property. The first thing the “original” property owner assumes it that the new home must be draining on his or her property and causing the standing water. After all, the new lot was raised higher than the adjacent (it had to be due to Federal minimal flood elevations for new construction). While occasionally it is the new construction causing the problem, most times it is actually the first property that is at fault. In many of these situations, the first property actually drained towards the second. This worked fine when the second property was a vacant lot, lower than the first. But when the second property is developed as the code and federal flood regulations require, the first lot can no longer drain onto the second and therefore the water has no where to go. In these situations, the first lot owner is responsible for re-grading his or her property such that it will properly drain towards the street.
During the new construction process, we require that the lot being developed drain to the street and NOT on to any adjacent property. We inspect each site during and after construction to make sure this is the case and will not issue an occupancy permit for construction until we are convinced that the new site drains properly. However, we can not require new development to accept runoff from other properties.
If you have a drainage problem in Ocean City, please feel free to contact the Engineering Department at (410)289-8845. We will be happy to meet with you, determine the cause of the problem and try to work out a solution. We will get back to you with our findings quickly, however the actual repair may take some time, please be patient, we currently have a backlog of over 200 storm drain and pavement repair requests, and remember, sometimes the solution may require corrections to your own property at your expense.
As I discussed above, storm drain runoff in Ocean City discharges directly into our bay. It does NOT go to the sewage treatment plant. Anything you dump into a storm drain inlet will go directly into the bay. If you don’t want to swim in it, don’t put it in the storm drain! So enjoy Ocean City, you’re on a beautiful island surrounded by beautiful clean water, don’t let the occasional puddle ruin your day.
Terence McGean, P.E.