How-To

Monitor and Protect Earthen Lagoon Berms
Dan Pusey, Facilities Planning and Don Jones, Agricultural and Biological Engineering

 

Lagoon Berms - Danger Signs

Wave Damage on inside of berm

Seepage on outside of berm and several feet out from toe of berm

Development of very damp, soft areas, slumps or bulges on outside face of berm

Rodent burrows (usually around cleaner water in second or third cell lagoon-Remove animals and backfill dens)

Be vigilant of earthen structures - especially those that have berms elevated several feet above grade

 

Lagoon Berm Failures

image #1 - lagoon berm failure

image #2 - lagoon berm failure

image #3 - lagoon berm failure


 

This screen above shows the catastrophic failure of an earthen bermed lagoon. Since an earthen berm settles at different rates, some spots will always be lowers than others. Any lagoon overflow will find these low spots and through erosion will create an ever wider and deeper opening, eventually causing failure of the berm.

An emergency spillway, if allowed in your state, should always be used if at least one side of the lagoon is at grade. Install a well-sodded waterway 1:5 slope or less near the grade level side of the lagoon to divert excess water rather than allowing the berm to overtop. Set the emergency spillway at 6" below the level of the berm. Certainly any lagoon overflow should be avoided if at all possible, but a small trickle of overflow is certainly preferable to total failure, and can be corrected with considerably less damage to the environment. If the all sides of the lagoon are above grade, an earthen emergence spillway will not be feasible. Consider instead a large metal or plastic pipe overflow that discharges in an area that is readily observable by the operator.

 

Lagoon Berms - Protecting Against Failure

Thoroughly inspect berm every month or after large rainfall

Look for low or bare spots, start of rills or gullies on berms - if found, fill with soil, compact, reseed, mulch with straw. Irrigate if necessary for good stand

Keep grass on berm and emergency spillway mowed and fertilized to create thick sod and make inspection easier

Monthly inspection of lagoons berms by a knowledgeable person is advisable. Even more frequent inspection is recommended in some states.

Keep earthen berms and the area around a lagoon well-trimmed facilitate inspections and to make the area less inviting to burrowing rodents.

Prevent growth of trees and bushes because root system can lead to seepage and shelter burrowing animals

Replace all moved, settled or destroyed slope protection such as riprap or concrete paving

Maintain fence and warning signs

Consult a Registered Engineer, local NRCS or the state natural resources office for assistance if needed

Be especially careful in "raising" the height of earthen berms to increase the capacity of the storage. A knowledgeable engineer and contractor are needed to ensure that the added fill height is properly compacted and keyed into the existing berm to create a sound structure and prevent a potentially dangerous situation.

Each state should have state-level expertise in earthen water storages and earthen dam inspection. Often, NRCS can offer engineering assistance and state land-grant universities may have extension publications that will be useful in maintaining a safe lagoon system.

 

Lagoon Berm Inspection

 

Inspect earthern berms every month for damage

This sketch shows some of the things to look for when inspecting an earthen lagoon.

 

Lagoon Berm Design

 

Earthern berm designed to minimize wave damage

This is an innovative method of lagoon construction, designed to lessen the effect of wave action on an earthen berm. This is becoming a more serious consideration as lagoons become larger, and as lagoon surfaces are often elevated 10-15 above grade where wind speed is greater.


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