Drainage Design Solutions of Different Topographies

Question:

What is the best approach when designing fields for drainage?

Answer:

Based on our experience designing 100,000s of acres, we have come up with these rules of thumb:

Flatter Fields Suit Landforming Alone:
On fields with relatively low slopes (e.g. less than 0.5%) then there are often many small shallow depressions. Landforming is generally the best solution as minor cutting and filling can solve the problem most cost effectively.
Fields Not Steep and Not Flat Suit Landforming & Drains Combined:
Between the flat and steep categories (e.g. 0.5% – 1.0% slope), the solution is generally a combination of ditching and landforming.
Steeper Fields Suit Drains Alone:
On fields with higher slopes (e.g. greater than 1%), the flows paths are often easily defined and larger deeper depressions may exist. Cutting drains between the depressions is probably the most cost effective solution and putting the cut soil in the depressions can raise the required elevation of the drain network and reduce the total cut volume.

Below are examples of these three different design styles in action.

Flatter Fields Suit Landforming Alone

Existing Topography

Existing Drainage Analysis

Proposed Topography

Proposed Cut/Fill Map

Fields Not Steep and Not Flat Suit Landforming & Drains Combined

Existing Topography

Existing Drainage Analysis

Proposed Topography

Ditch Long Section

Ditch Cross Section

Note: Vertical is exaggerated. This example shows a drain channel about 0.8ft deep with 15ft wide flat base that batters up to the surface at 1:20.

Steeper Fields Suit Drains Alone

Existing Topography

Existing Drainage Analysis

Proposed Topography

Note: This complex ditch network is not actually 60ft wide. It was just designed as so to create a flat base to have a reference for the control file. The scraper will only follow the center line.

Proposed Main Ditch Long Section