Saturday, September 12, 2009

All Topographic Surveys are not Created Equal

Imagine that you have a nagging pain in your knee, and based on what you’ve heard and speaking with a few of your friends, you decide that you need an x-ray. So you go out and get an x-ray of your knee – you may even shop around first for the best price if you’re paying in cash. Then you show up at your doctor’s office with your films in hand, proudly proclaiming that you’ve already obtained a knee x-ray. But when the doctor starts asking you questions about your knee, he determines that it’s probably arthritis, and to get to the root of the problem he needs to order an MRI, and even a few more x-rays – this time from the correct angles and positions.

Most people wouldn’t handle their medical problems in this manner – not speaking to the doctor first would be like putting the cart before the horse – and a Radiologist who just did what you said and took an x-ray of your knee, without an order from your doctor first or without asking any questions, would be doing you a disservice. But that’s how many good, honest landowners, deciding to develop all or part of their property, start out by simply ordering a ‘topographic survey’ to get the ball rolling.

One of the most important parts of the site development process is getting a good survey. Unfortunately, it’s also one of the first things you do; so many people enter into the decision with very little knowledge of what the project will entail. Getting input and advice from your civil engineering or surveying professional with knowledge of the local codes and procedures is vital to getting your project started off on the right foot.

Why it matters

You may wonder why it matters so much – after all, you can always have your surveyor pick up ‘a little more information’ later if it’s needed, right? But at what cost to the project? Besides the actual costs to re-survey the new area, what if a major design decision is made based on the topography shown – and then you find out later that this portion of the site was obscured from view, or ‘approximated’, because at the time of the survey it was not considered part of the development area? It may cost a few thousand dollars or more to have several design consultants change their plans. Or even worse, what if it’s discovered at construction that what you thought was a 6 foot high retaining wall really needs to be 12 feet high because of inaccurate topo information? Besides the cost of several thousand dollars (and sometimes a lot more) to build the additional wall, and the delays that will ensue, will the local agency even let you build a wall over 6 feet high?

What to Do

For many types of development projects, you’ll need a solid, comprehensive topographic survey to cover all of your bases. This may include a combination of detailed aerial and ground-shot information, to limits well outside of your property boundaries, with a boundary survey if your parcel warrants it. But for many smaller projects, your budget may dictate that you do only what’s needed and not too much more. For these kinds of projects, before proceeding, ask yourself and your design professional some key questions about:

  • Important Design-Driven Elements – If it’s critical to know where and how high your neighbor’s house is because of a beautiful view, including it in your survey is a must. Are there a few trees that you simply must keep? Then their trunk and drip line locations should be included.

  • Location of Existing (potentially conflicting) Features – The location of existing utilities, such as water lines, utility boxes, power poles, etc. may be vital in driving your design decisions about driveway or structure placement, grading, and landscaping. And don't forget about existing septic systems, both on your site and on an adjacent site - such information could literraly make or break your project.

  • Precision – If you’re going to make use of existing structure, hardscape, and landscape features on your site, then you may need precise spot elevations and positions for those features. If you’re just going to demolish existing features and start over, then this level of precision is usually unnecessary.

  • Conditions on Adjacent Properties – We’ve seen many well-drawn, detailed ground-shot topographic surveys of urban sites, only to find out later that the next door neighbor has a 5 foot retaining wall/drop off right along the property line which would severely inhibit what we can design on our side of the line. Or a brow ditch may be constructed just on the other side of a common property line – an important feature when considering the drainage design of the property.

  • Municipality Requirements – You may think that your remodel only requires you to collect topographic information within 30 feet of the existing house because that is the limit of your proposed work. But if you’ll later need a grading or discretionary permit, the agency may dictate that your entire site, plus an additional distance beyond your site, be included. Does the fire department require existing hydrants within 300 feet of the property be shown? Do you need to show existing street improvements to the opposite side of the street? Best to gather this information during the (first) survey.

  • Thick Brush and Vegetation – Aerial surveys rely on line of sight from a plane flying overhead, so features below heavy tree canopy will not be clearly defined by an aerial. If brush is thick even at ground level in an area of importance, consider partial clearing to allow for some shots to be picked up by your ground survey.

  • Vertical Benchmark – Not having to search for and tie in a recorded vertical benchmark is less time consuming for the surveyor, but for most projects, tying in an agency-recorded benchmark is required to demonstrate to the agency and the surrounding neighbors the actual elevation of the features of your property when presented for review. Be absolutely certain that it won’t affect your project before you allow an assumed benchmark be used for your survey.

  • Boundary Lines – For certain properties, generally those created by deed only and without a recorded map, a boundary survey, and the corresponding setting of field monuments/property corners, will be required in addition to your topo.

  • Below the Surface – Features of your property that can’t be seen in the field, such as easements, setbacks, and underground utilities, are critical features that should not be overlooked. Make sure your civil engineer or surveyor can research and plot these for you on your final survey drawing.

The Bottom Line

Being too hasty in ordering a ‘simple’ topographic survey can turn out to be quite costly later. Speaking or meeting with a knowledgeable design professional beforehand will go a long way toward avoiding unnecessary delays and expenses. And if you decide to competitively bid your survey, create a comprehensive list of requirements first so you can compare apples-to-apples from prospective companies. We like to say that when it comes to site development, if you do nothing else, get a good survey – it’s the best insurance you can buy for your project.

John S. Coffey, PE, is founder and President of Coffey Engineering, Inc. in San Diego. He’s contributed to over a thousand civil engineering, surveying, and planning projects in San Diego and surrounding communities over the past 14 years. 858-831-0111