There are many good designs and the best depends on your application. Other than sharing our experience, we cannot make more specific recommendations because all applications are different.
Access and Placement
We learned early on to build a nice roadway around our projects for easy access with equipment and recreational activities. Our roadways are made from compacted soil and graded to shed water. We place them immediately adjacent to the water, on top of the pond berm or along the edges to provide access around the entire surface. We mow the roadways to encourage grass growth and minimize rutting and erosion.
We place our water level control boxes beside our roadways for easy access with equipment. We widen an area in the roadway near the outlet to accommodate the water control box where it is out of the traffic path.
Two or More Water Level Control Boxes
In applications where wildlife habitats are seasonally flooded, two or more water level control boxes may be used to split water between multiple habitats. The stop logs can be adjusted to stop flow to the pipes feeding the habitats and divert all flow to the drains when we want to dry the habitats. The stop logs can be readjusted to divert water flow to the habitats and stop the drain when we want to flood the habitats.
Dealing with Flood Water
There will always be the possibility of storm water over-running the drain. Or, the drain could plug up even if it is adequately sized. A good design must plan for these contingencies. Our grass-covered roadways easily withstand occasional floodwater overflows.
In areas where overflows can be excessive or frequent, we create spillways which are shallow channels across the roadway packed with riprap and topped with 1 ½ gravel and some soil. Grass will grow though this and it becomes very resistant to erosion. These are dry most of the time. Flood water will flow harmlessly across the spillway until the drain can catch up with the flow.
Always consider contingency plans for storm flows. We have worked on lakes with very large outlet drains that occasionally over-run the pipe and into the emergency spillway. We have also worked with tranquil ponds that collect water from large drainages. These ponds normally have no outflow but can become torrential rivers in a storm. We had an experience in the Sonoran desert where a tiny trickle of water in a wash would occasionally swell into a six-foot-deep, 120-foot- wide raging river during monsoon season. In that case, the wash was draining 25,000 acres of normally bone-dry desert. The back side of our 80-foot-long, 20-foot-wide, 4-foot-thick concrete overflow pad was undermined after a particularly bad storm. The point being there will always be a bigger storm -- you will never have a large enough pipe!
Just a trickle… most of the time!
Consider What Is Downstream
Your design must consider the potential consequences of damage to downstream property, structures, roads, etc. should a breach occur.
We once repaired a large lake built many years ago. We opened the drain gate and thought little of it until we realized we had flooded the road a mile downstream. Fortunately it is in a rural setting and there was no damage but we learned a valuable lesson. We limit our projects to relatively flat ground where the potential from a dam, dike or berm breach is insignificant. We do not worry about a breach because our downstream areas are grassy meadows, wetland habitats or wooded areas capable of safely receiving the entire contents of the pond if the berm were to breach.
Waterfowl Habits
Small wetland habitats with grassy and woodland boundaries attract a wide variety of wildlife. In addition to aquatic life and waterfowl, we have observed many animals including songbirds, deer, beavers, muskrats, racoons, turkeys, herons, cranes, owls, eagles, otters, bobcats, foxes, javelina, coati, and others.
Habitats are most productive when properly managed to encourage an early succession ecosystem. This basically means an area that has natural grasses that grow in seasonally flooded conditions. These ecosystems produce abundant seeds and support dense invertebrate populations that are the main source of food for waterfowl.
If the ecosystem is flooded for too long, too deeply, or kept dry for too long, undesirable plants will grow and the ecosystem will be less productive. In the extreme example, it will turn into a swamp which is basically a shallow lake with trees.
Successful management requires that the water levels be drawn down at appropriate times to eliminate standing water while maintaining moist soil conditions then reflooding the areas at the appropriate times to maintain the ecosystem. In practice, we allow our habitats to progress through various stages allowing some woody vegetation to emerge before we intervene because we found that cover is also an important factor.
We enjoy fishing and usually include a pond to maintain aquatic life when the water levels are lowered. Sometimes this is just a deep hole near the drain end. Sometimes we create the habitat portion as a wide shallow ledge surrounding a pond in the center. Fish benefit greatly from the shallow habitat areas in the transition months.
There are many good Internet articles and videos on this topic. Here are a few of our favorites that illustrate the topic:
https://www.fws.gov/sites/default/files/documents/Moist%20Soil%20Guidlines.pdf
Common Terms Associated With Our Products:
Water Level Control
In-Line Water Level Control
Water Gate
Pond Drain
Lake Drain
Water Impoundment Drain
Retention Pond Drain
Flashboard Riser
Flashboard Drain
Flashboard Inlet Structure
Drop Board Riser
Drop Board Inlet Structure
Drop Board Pond Drain
Flashboard
Stop Log
Weir
Habitat Water Control
Water Level Management
Wildlife Water Level Management
Monk
Pond Monk