Ever since Philadelphia began taking its waterfronts seriously a decade ago, it has dreamed of shores lined with lithe, elegant, Vancouver-style towers. Master plans were assembled, new recreation paths were laid, parks were created. Yet only a few high-rises have materialized, none of them the least bit thin or urbane.

That may be about to change. Developer Carl Dranoff is planning a 21-story apartment building on the Schuylkill that has the potential to raise the bar for all waterfront design in Philadelphia.

Or not.

Before we venture further, a strong note of caution: The project is still at an early stage, when only the site plan and the tower's basic form, or massing, have been established. We don't know crucial details, like the color of the building or the material. But the tower's profile is svelte enough, and its architect good enough, that it is possible to imagine something special emerging. Then again, we should keep in mind that Dranoff is the same guy who gave us the giant Pepto Bismol bottle called Symphony House.

Dranoff's new high-rise, designed by Cecil Baker + Partners, would literally be a tower in the park, and would be known as One Riverside Park. The building would straddle the southern end of a triangular parking lot at Locust and 25th Streets, wedged between the Schuylkill River Park Community Garden and the entrance to the Schuylkill Banks trail. The rest of the triangle would be filled, sadly, by a garage.

The specialness of the landscape can't be overstated. Close to a million visitors a year converge on this small paradise, which includes the trail, basketball courts, lush picnic lawn, children's playground, and the city's most deluxe dog park. The Nutter administration just spent $4.6 million to upgrade the park and connect it to the trail, and the collection of urban amenities has blossomed into a citywide, and even regional, draw.

Given all that, the project's most appealing feature is a small cafe that would sit at the northern end of the triangle, surrounded by a landscaped plaza with outdoor tables. Greeting joggers and walkers as they stream onto the trail, the cafe would provide a refuge that the Schuylkill Banks needs.

It's easy to understand why Dranoff was attracted to the site. It offers sweeping views of the river and skyline, yet it is still thoroughly embedded in a lively urban neighborhood. Since it is already zoned for tall buildings, a 210-foot-plus tower can be built without the fuss of obtaining a variance.

Obviously, the public's concerns are different. Many would agree that a parking lot is far from ideal on the lovely waterfront. But can a large tower possibly be integrated into this beauty spot without damaging either the park or the neighborhood?

While Dranoff would not discuss his plan in detail, it is evident from drawings available online that he and Baker face an extreme challenge.

In our desire for an esplanade lined with slim towers, we often forget that waterfront property usually sits in a flood plain. The threat of even occasional high water requires developers to elevate their buildings by at least a story.

Without creative design and a commitment to the public good, the result is usually an empty ground floor and long blank wall. The flood plain is one reason that Marina View, a midrise proposed last summer for a site next to the Ben Franklin Bridge, was so disheartening. Dranoff's one-story garage is similarly lifeless - and faces a heavily used pedestrian street, no less.

Dranoff's tower has the advantage of presenting its narrow side to the street. But the east-west facade will form a long wall, approximately 144 feet, across the park's northern border, now occupied by the community garden.

With the limited information now available, it is hard to know what this wall will do to the park. Because the tower borders its north side, shadows won't be much of an issue.

But what if Dranoff succumbs to the current vogue and clads the exterior in an all-glass skin? The heat reflecting off the surface would "cook" the park, particularly the community garden, says John Randolph, an architect who lives on 25th Street who helped create the Schuylkill Banks trail. (Full disclosure: I currently coddle some tomato plants in the garden.)

That's not just speculation. A new glass tower across the street from Renzo Piano's Nasher Sculpture Center in Dallas has broiled the museum's exquisite grounds.

Cladding the tower in masonry would cut down on the heat. It is essential that Dranoff provide detailed sun studies so we can better understand the effects of the shifting light and shadow on the park. How Baker treats the building's south facade at ground level also is important. He should consider moving the loading dock, now facing the park, to the parking entrance.

Right now, the developer envisions the project as a rental building, with 167 units. But this luxury location cries out to be condos. It would allow Dranoff to reduce the number of units, and the parking demand. The building's underground parking might then be sufficient.

While One Riverside Park doesn't require zoning approvals, Dranoff must make a stop at the Planning Commission's new Civic Design Review board. The reviews there so far have been perfunctory. This tower is a chance for the members to show their civic gumption.

One Riverside Park won't be the last tower to work its way onto Philadelphia's lovely Schuylkill waterfront. There are three parking lots between Walnut and Cherry Streets, waiting to be developed. It would be terrible to squander this glorious public amenity used by thousands of urban residents for the views of a few.