Soccer Fields vs. the Oak Grove: A 12-Acre Programming Conflict
A 12-acre community park falls about 30 ft from its northwest corner (elev. 130) to its southeast corner (elev. 100) over roughly 900 ft. The program calls for two 360 x 225 ft natural-turf soccer fields that must hold within 1 percent grade, a 60-space parking lot, a playground, and a restroom. A 35-tree stand of mature oaks (18-30 in. DBH) occupies the gentlest third of the site - the only area flat enough for paired fields without major earthwork. Native soil is a clay loam with a measured infiltration rate of 0.1 in./hr. The budget is $1.9M, and local ordinance caps impervious cover at 20 percent (about 1.05 ac). The client says: "Just flatten the oak grove - trees can be replanted."
1. The client wants the fields in the oak grove. Frame the decision quantitatively - what do you measure or compute before recommending an alternative?
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1. Convert the tree loss into an actual quantity. Protective radius is roughly 1 ft per inch of DBH, so a 30-in. oak has a ~30-ft critical root zone. Two 360 x 225 ft fields plus 15-ft safety margins cover about 4.4 ac - there is no arrangement that fits inside a 35-tree grove without grading through most of those root zones. Plan on near-total removal of the stand, plus a tree-preservation permit review and mitigation fees where ordinances apply. Replacement caliper stock does not restore canopy, shade, or stormwater function within the life of the facility.
2. Price the alternative honestly. Orient the field pair parallel to the contours and set the field plane at the mean elevation. On a 4 percent cross slope, that leaves cut on the uphill half and fill on the downhill half - order of magnitude: 4.4 ac (~192,000 sf) at ~3 ft average cut/fill is roughly 21,000 cy. At $25-40/cy to excavate, place, and compact, that is a $500k-$800k line before drainage, and the fill side must be engineered and tested rather than end-dumped.
3. Test the program itself. A third and fourth option usually beat both: one regulation field plus one multi-use lawn on the flatter ground, or a single field with a shared-use agreement at a nearby school. Sports-field demand is often peak-hour demand; two fields that drain poorly serve a program worse than one that drains.
4. Check the overlays. Confirm the impervious cap: 60 stalls at ~350 sf plus aisles is roughly 30,000 sf, plus restroom and walks, landing near 0.8 ac - under the 1.05 ac cap, but only if the ordinance does not count compacted field subgrade as impervious.
5. Present a comparison matrix, not a verdict. Rows: earthwork, tree loss and mitigation, stormwater/detention, schedule, maintenance cost, program capacity. The grove is not the cheap option once removal, mitigation, and lost canopy are in the matrix.
2. Assume the fields move to the sloped ground. What grading, soils, and stormwater moves decide whether that scheme actually works?
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Earthwork balance. Balance on site. Importing or exporting 20,000 cy is a budget-killer; adjust the field plane elevation until cut and fill are within about 10 percent of each other.
Fill is the risk. Strip topsoil first and stockpile it for the field surface. Under the fill side, strip organic material to suitable bearing, scarify, and place fill in 8-12 in. lifts, compacted and density-tested. Untested fill under a 1 percent field will settle differentially, and a field that ponds in the middle after two seasons is a failed project. Allow for settlement or specify a period of surcharge.
Keep water out of the field. The 1 percent field grade only works if surface water from the uphill 5-6 ac is intercepted before it reaches the field. Use perimeter swales at 1 percent minimum, sized for the developed condition, and daylight them to a detention facility rather than to the property line.
Do not count on infiltration. At 0.1 in./hr, native soil provides essentially no infiltration credit. Detention must be surface storage with a controlled release; if the ordinance requires recharge, that credit has to come from an amended engineered soil or an alternative BMP approved by the reviewer.
Compaction vs. drainage. Turf fields are compacted by design for playability; that is the source of the drainage complaint the owner will call about. Budget for a sand-cap or amended profile, or accept limited winter play.
3. The client accepts a phased build and wants construction to start in eight weeks. What goes on the tree protection and sequencing plan?
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Protection plan content:
- CRZ radius at 1 ft per inch DBH, tree by tree, drawn on the grading plan, with a tree schedule (species, DBH, condition rating, disposition: save / remove / relocate).
- Tree protection fencing at the CRZ line (not the drip line), installed before any equipment arrives and shown on the demolition and staging sheets.
- No grade change, no stockpiling, no fueling, no concrete washout inside the fence. Where grade change is unavoidable within the CRZ, specify aeration, root-pruning by a certified arborist, and a monitoring schedule.
- Access routes and staging areas located outside all CRZs - this is the item most often missed in phasing documents, and it is what actually kills the trees.
Sequencing:
- Install fencing and tree protection, then demolition.
- Strip and stockpile topsoil from all areas to be graded (do this before earthwork, not during).
- Rough grade and place fill; allow settle time before fine grading.
- Utilities and drainage structures - trenching inside a CRZ is as damaging as grading.
- Fine grade, topsoil, and plant in the appropriate season (fall for bare-root; spring if irrigation is available).
Tie to the contract. Show the fence on the drawings and require it in the specifications. An unenforceable note on a plan sheet is not tree protection.