slope development

[KPBCMP]

I am a program administrator for a regional government in Alaska. Working with policies written more than 10 years ago, I am often left wondering about the reasonability of certain policies. Recently, State Forest administrators have questions about our recommendations for limits on road construction based on the policy below. Please let me know if there are reasonable engineering concerns which are addressed in the policy. Thanks!

"Erosion : [Administrative Policy] - The following performance standards should be considered for development on slopes exceeding 15 percent

"a. For slopes of 15 to 30 percent, the area used for development should not exceed 25 percent of the site.

"b. For slopes of 31 percent or greater, the areas used for development should not exceed 10 percent of the site.

"The areas used for development include all structures, roads and driveways.

 

[Focht3]

Do you know who produced the requirements? I'd suggest that you contact those individuals first. This should save you a lot of time - and effort.



Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ishvaaag]

In any case and where site is wanted mostly clear seems sound policy. The main point is that keeping plot ocupation low, both the environmental quality of the sloped site and the maintanaibility of the planted structure are greater.

Of course if ample development pressure is occurring it means that land value is already being pressed upwards, and then the bigger distances cause what to developers look as an unnecessary high cost.

 

[72shortbox]

I'm not sure how they came up with the 10% and 25%, but I think the rational behind it comes down to stormwater infiltartion and runoff velocites. The more development the less perviouse area which increases runnoff. As the slope and runnoff volume increases the velocies rise which can carry sediments off site.

 

[cvg]

I think you are right. I have seen similar policies for development on alluvial fans/terraces in the desert southwest. This allows a non structural approach and minimal increase in runoff in natural desert areas, reducing erosion and sediment transport.

 

[jdmm]

I can't comment on your specific guidelines but having been faced with creating similar guidelines I offer the following comments:

Guidelines must limit the maximum allowable slope. This might be 1.5(horizontal) to 1(vertical) or 2(h):1(v) or something in this range.

The guidelines might consider a maximum height of retained soil such as 2.4 m (8 feet) as in the case of a basement wall.

In consideration of these constraints they create geometric constraints to development.

How these specific guidelines were developed is not clear since there is no indication of the size of the "site".

If you try to draw the requirements in section and in consideration of stable slope angles you might determine the intent of the regulations and their appropriateness.