Drainage Pipe Slope and Trench Depth Calculation

hey what's up you guys it's scott with everyday home repairs and today i want to help you through the planning process to know how deep do you dig a trench when you're landing a drainage line for a downspout or maybe a sump pump discharge in my exact scenario i have both of those i have a downspout and a sump pump discharge that's kind of temporarily routed and dumping out into my yard and kind of making a swampy mess so once and for all i want to run those permanently through a single wall corrugated pipe and away from the foundation so i don't have to worry about it there's just a couple things you need to take into consideration so let me walk you through on the whiteboard behind me how to calculate those so you can make the plan and know exactly how deep to dig that trench and maintain the proper slope for your drainage so if you just know the actual length or run of your drainage you can do the calculation to know what type of rise or elevation change or you're going to have to account for to make sure the water drains through the pipe what you'll do is just use a simple calculation which is rise over run equals slope now because i'm using single wall corrugated pipe i'm going to use 1.25 percent but if you were using like a schedule 40 pvc you could use one percent and be okay so i do know my run which is 36 feet or if i multiply by 12 i can get the number of inches at 432 inches so i know my rise over 432 inches equals 1.25 percent we'll rearrange that equation a little bit so we will multiply the 1.25 percent and put that in decimal form so you just move the decimal place two spots here so that's 0.0125 times the 432 inches of run and that's going to give us our rise at four point sorry at 5.4 inches i'm going to round up and i'm going to go with six inches so that's what i'm gonna plan to need an elevations change from the start to the finish the finish of my pipe should be six inches lower with a consistent slope along the run so now we know how much elevation we need or rise we need for the project and that is going to be a critical piece that we're going to use in planning out how deep to dig the trench now each of our yards is going to be a little different some are going to have extremely flat yards some are going to have hopefully not too much of a negative slope back to the house that is not something you want to have and then some are going to have a very aggressive slope away from the house in my case it's overall pretty flat but i do have about a foot elevation change the way i found that was just using string two stakes and a line bubble level and if you don't know how to do that you can check this video right here and i'll walk you through the full process but that is where i'm going to get these measurements from is referencing that level line so if you don't know how to do that jump back on that video get a little bit more information and then you can jump back and this should make more sense so trying to get as close as possible to these numbers here so you can see how i calculated everything and then apply that to your application so i have my house over here downspout which is one of the main lines but also the sump is going to come right in here this is my starting point so with my green line here this was my level line that i put in the yard i measured at the starting point nine foot out i took a measurement 18 foot out 27 foot out and 36 out so i just had multiple reference points that i marked with an orange marking spray paint in the yard so those will be my references that i'll be checking my depth when i'm digging the trench at the starting point here from the level line to the actual ground was 12 inches now i'm going to use this to know how much the ground has either come up in elevation stayed the same or down an elevation and that's going to help me know from the ground surface at each of these points how much do i need to dig down to set the pipe in the bottom to maintain that 1.25 percent slope now i do have a starting depth here where i have four inches of corrugated pipe and then 10 inches of dirt on top of that so the trench depth at the start i'm going to be doing 14 inches now i take that same 14 inches and i know across one quarter of my length i need to lower 1.5 inches for my slope so i'm going to add that on to the 14 but i'm also need to add on two and that's because at my nine foot mark here my ground actually comes up it comes up two inches so thus i have to dig from the ground level i have to dig a little deeper to maintain that slope of the corrugated pipe that can be a little confusing but something critical that you need to account for because if you don't account for the undulations of your ground your pipe is definitely not going to drain properly so all that added up at my first nine foot marking point i know the depth needs to be 17.5 inches below the top surface and that will give me my little over 1.25 percent grade now if i go out to my next mark again i'm going to take that starting 14 inches i'm going to add on three inches for the slope right 1.5 inches here three inches now here to maintain that slope and i know both of these starting point and this point are 12. so there's no additional compensation made so i know the dig depth needs to be 17 inches at my second checkpoint then i go to my third checkpoint here i again take 14 inches i'm adding the slope and now it is 4.5 so it's 1.5 here 3 inches here 4.5 inches here but now i'm actually subtracting three inches and that's because the ground is starting to go down it's starting to slope down and that is signified by 15 inches between my level line and the ground surface opposed to my starting 12 inches so if you if you add this up to 18.5 and then you subtract your three inches you get i'll need to be 15.5 inches below the surface at my third checkpoint and then at the end of the run at the end of the line where i'll be putting in my pop-up emitter here i'll take that 14 inches i'll add six inches and that's my total slope needed my total rise needed throughout the run of the corrugated pipe and i'll subtract off 12 because this is actually 24 inches from the level line to the the ground level so i compared 12 inches to 24 that's 12 inches difference and i subtracted that off so adding the 14 and the six you get 20 you subtract off your 12 and that's i'm going to need to go 8 inches down which is great because it is something i also need to account for is the actual pop-up emitter itself i can't sink this 14 inches because then the pop-up emitter would be there and i have to do like a connection pipe and that's just not ideal so eight inches is actually going to be pretty close to what i need here because it's about seven inches from the bottom here to the top of this 90 degree elbow so i'm not sure how much you guys love or hate math but that is how i calculated it and i'm going to take that 9 foot 18 27 foot in the end of the run that's where i'm gonna be checking my trench step and then just using a two by four in the middle to make sure it's a smooth surface between each checkpoint that's my plan for my project i'll be doing that later on and there'll also be a video on the overall complete drainage project that i'm doing now if you have any questions there's a lot of different scenarios when it comes to drainage that you have to account for and each one of our yards or properties is going to be different so jump down in the comments let me know and i'll help as much as i can and finally if you haven't already and you like this sort of content don't forget to subscribe to our channel we have multiple videos coming out per week to help you with repairs and improvements around the house and we'll catch you on the next one

Channel: Everyday Home Repairs

Views: 10,827

Rating: 4.9509201 out of 5

Keywords: drain pipe slope, downspout drainage solutions, downspout corrugated pipe, downspout extension underground, sump pump, sump pump drainage outside

Id: qsduSLrGCjA

Length: 8min 39sec (519 seconds)

Published: Thu Apr 29 2021