Would Wetlands Solve the Problems in Ravenswood and President's Ponds?

Designed By The De-Eutrophicators

Engineering Senior Design Team 10: Phil Blonn, Jon Lefers, Mark Loerop, Renee Van't Land, Lora Vandenberg

This page is based on the 1999 poster session

Background:

Ravenswood and President's Ponds are detention ponds for storm water runoff from parts of Calvin College, Grand Rapids, and East Grand Rapids. They are an important part of the region's stormwater management system, and the outflow water eventually flows into Reed's Lake. These ponds are currently undergoing the process of eutrophicaion: an increase in turbidity and plant growth, and a decrease in variety and quantity of fish. The process of eutrophication is accelerated by excess of nutrients from pollution in the water. Since these ponds receive stormwater, they receive nutrients, fertilizers, and debris which are washed off of lawns, roofs, driveways, and roads. The present condition of these ponds is "productive eutrophic". If lend unattended, these ponds will eventually fill in and become marshes, loosing their detention capabilities.

Proposed Solution:

It is proposed that the ponds be dredged and that a wetland system be created on the south side of the ponds. The dredging will clean the current overload of nutrients out of the sediments in the ponds. The wetlands will receive the future inflow and improve its quality before releasing it to the ponds. Cleaner water in the ponds will prevent the growth of an abundance of aquatic plants by reducing the quantity of chemical nutrients and debris in the water. This change in water quality will provide a larger and more diverse life system. The details of the solution and an outline of how it works are presented below.

Description of Wetlands System

The following numbers correspond with the numbers on the wetlands drawing. They show the chronological path that the water follows. .

1. Swale. Water from the East Grand Rapids and Grand Rapids/Calvin College inflows are combined in this swale which directs their flow to 2.

2. Sediment Forebay (SF). The SF has a cross sectional area of 55 square feet, which is large enough to decrease the velocity of the incoming water to a point where particles larger than D30 of the incoming sediment will settle to the bottom of the forebay within 120 feet. Once the inflow enters the SF, it will fill the SF until the water is at a depth equal to the height of the first berm (3).

3. Berm. Once the SF is filled to an elevation of 752.2 feet, the elevation of the top of the berm, the water will sheet flow over the berm into the wetland (4).

4. Wetland Area. As determined by an optimization calculation, 0.3" of runoff off the entire watershed (2.5 acre-ft.) will be the maximum detention of the wetland. For reference, a 2-year storm generates approximately .5" of runoff. The maximum depth in the wetland is 3 feet. In larger storms, after the wetland fills to 3 feet (holding 0.3" of runoff), the overflow system is used. The overflow system is described in parts 6 and 7.

The wetland area has varying depths shown in the contours on the wetlands drawing. When the wetlands area is full, the depth of the water ranges from about 1.5 feet to 3.5 feet. These varying depths allow for the growth of a greater variety of wetland plants. The wetland is designed to drain within three days of a storm, allowing the plants to absorb the nutrients from the water. During this time, water slowly permeates/drains through the berm into Ravenswood Pond described in 5.

5. Berm with permeable section. A cross section of this berm is shown on the plan and profile plot. The top foot of this berm is topsoil. The bottom three feet of the berm is constructed with a permeable mixture of coarse sand/pea gravel as a core and with rip rap on both sides. This berm allows water from the wetlands to drain to the pond at a controlled rate. The sand/gravel mixture should be chosen and compacted such that the conductivity allows the water to drain in three days.

OVERFLOW SYSTEM

In storms greater than the 2-year storm and in consecutive smaller storms, the over flow system will be used. In these storms, the "first flush" of nutrients will still be treated in the wetlands. The remaining water will bypass directly into the ponds through the following progression:

6. High Point. The high point is at an elevation of approximately 752.5 feet. When the water in the wetlands and sediment forebay reaches the level of the high point, all the new inflow will start to flow over this point and into the overflow swale (7). Note that at this time the berm described in (3) will be covered with water.

7. Overflow Swale. This swale will handle the flow of all water that overflows the high point. Since this flow is not part of the first flush and does not contain many nutrients; therefore, it will not be treated but will bypass the wetlands and flow directly into Ravenswood Pond.

Notes:

Part 2: In dry periods, it is estimated that the ground water table will cause a depth of two to three feet of water in the sediment forebay to be maintained. The forebay empties to that level because a 15 foot section at the west end of the berm in 3 is composed entirely of rip-rap, allowing the water to drain. Because of the constant water source, aquatic plants may be planted here for aesthetic value.

Part 3: This berm is covered with sedge to prevent erosion. Sedge, not grass, is used because sedge is sturdy and does not need to be mowed. Small shrubs may also be planted in this area. The side slopes of the berm are 2 horizontal to vertical. Part 5: The top of this berm is covered with sedge. The gravel is graded such that no erosion of the gravel occurs. Larger gravel will be placed on the outside.

VALUE and CONCLUSION

The wetlands will be valuable to both Calvin College and the larger Grand Rapids and East Grand Rapids Communities. The wetlands will enhance aquatic life and create a unique and diverse plant and wildlife population which will provide a basis for academic studies. Furthermore, the proposal will give the area more aesthetic beauty and prevent severe fish kills. A path and observation deck could be incorporated through the area for students' and the community's recreation and education. In building the wetlands, Calvin College will be working in a cooperative effort with the local government to better the quality of the storm sewer system throughout the cities of Grand Rapids, East Grand Rapids, as well as the surrounding area. Since wetland systems are innovative, effective, and appealing, a wetland system at Calvin College will enhance both the image and quality of the college and its resources.