If we didn’t have rain there would be no construction stormwater discharge; there would be no erosion; there would be no sediment to worry about,with few exceptions. Without rain there is no need for sediment basins, silt fence or rolled erosion control products. Without rain, the construction stormwater professional is without problems (but also likely without a job).
Rain matters. Or at least it should matter. How quickly the rain falls, how long the storm lasts, the amount of time since the last storm, even how big the rain drops happen to be, can all contribute to the success or failure of our plans for construction stormwater management. The fact is – it is going to rain. And my suspicion is that in most cases, rain is not going to improve the productivity and profits of your construction project. In most cases rain causes more problems in construction than it solves. It’s just one more fact of life. The sun comes up every day, water flows down hill, and thankfully, rain happens. Right?
How much do you know about one of the most important factors in site work? Did you know that Mobile, Alabama receives about as much rainfall every year as Seattle Washington, but in a much shorter period of time? Did you know that a raindrop impacts the earth at about 19 miles per hour? Do you know that rainfall can saturate the ground rendering a vegetated surface impervious? Does your design and inspection reporting consider antecedent moisture?
What are the regulatory expectations for the basis of your analysis of pre construction and post construction hydrology in your state? How about the regulatory basis for design? What rain event would be considered an upset or be justification for bypass in your state? Does the type of size of the receiving stream matter? What does the 2 year, 24 hour storm event look like in your area?
Let’s say that you know the answers to all of these questions and that you are as passionate about the effects of rainfall on your project as you are college football. How are you gathering this critical data – the data that could impact your design effectiveness, your site’s regulatory compliance, your liabilities and risk?
If you are relying on the seasonal laborer to read or install the supermarket low bid rain gauge at one location on your 200 acre site, be careful. How you select the device, the location, frequency and process for rainfall data collection can have a huge influence on the accuracy and completeness of this very important data. Knowing the duration, intensity and quantity of rain that falls on your site today and what may have fallen yesterday is essential. This information can save your project and your tail, but only if you happen to be paying attention. A priority must be placed on collecting best information, and we must be very intentional about how we go about it.