Lew’s appointment gives him increased control over billions in contracting. (The Washington Post)

Updated 6:35 p.m.

Amid D.C. Water’s big announcement of a Bloomingdale/LeDroit Park flood relief plan comes other major news for the city’s water and sewer utility: Board chairman William M. Walker unexpectedly stepped down at Thursday morning’s meeting, effective immediately.

Mayor Vincent C. Gray (D) announced Thursday he’s appointing City Administrator Allen Y. Lew, who already serves on the board, to fill the chairman’s post.

Walker, the president and CEO of Walker & Dunlop, a Bethesda-based commercial real estate firm, spent an impactful four years atop the board. Appointed by Mayor Adrian M. Fenty, a fellow triathlete, the board under Walker’s watch made its most significant efforts to move past the lead crisis of 2004, appointing environmental lawyer George S. Hawkins to run the agency and approving a rebranding that turned the old Water and Sewer Authority into D.C. Water. The utility, which has yearly revenues of more than $400 million, also embarked on a number of ambitious capital programs under Walker, including the construction of a power plant fueled by sewage sludge and the groundbreaking of the $2.6 billion court-mandated “Clean Rivers” tunneling project.

The departure was not unexpected: Walker’s term expired in September, and his professional life has not gotten less complicated. Walker took his family firm public in 2010, and it has grown swiftly since. We’ve not yet been able to connect to discuss his particular reasons for stepping down now, but I will update when I do.

The choice of Lew to replace Walker is also impactful. The choice portends a closer relationship between the Gray administration and D.C. Water, which is governed by a mayor-appointed but interjurisdictional board. (Sewage from Fairfax, Montgomery and Prince George’s County is treated at D.C. Water’s Blue Plains plant.) It also puts Lew in a position to exert more control over the direction and contracting of those massive capital projects.

The New York native knows a thing or two about massive capital projects, having overseen on-time completions of the Washington Convention Center, Nationals Park and numerous rebuilt and renovated schools. But his control of spending and contracting methods have been questioned over the years.

Gray spokesman Pedro Ribeiro said Lew’s appointment does not represent an effort to exert more control over the authority. “It has everything to do with finding a strong leader to continue the forward progress at D.C. Water,” he said. “That’s really what it’s about — someone who’s a proven leader who has a track record for deliverables.”

Lew’s appointment, which is not subject to council review, is accompanied by other board moves: Adam Clampitt, a Capitol Hill public relations who ran for a D.C. Council seat in 2008, also announced Thursday he’ll be stepping down; he’s moving to Florida to be closer to family. To replace him, Gray is appointing Robert L. Mallett, himself a former city administrator whom Gray previously appointed to the Board of Elections. That appointment was derailed when it was discovered Mallet did not meet a length-of-residency requirement; the D.C. Water board does not have that requirement.

Gray also reappointed Alan Roth, an Adams Morgan trade association executive and former advisory neighborhood commissioner, to another four-year term.

Update, 6:35 p.m.: Walker, in a phone interview, said he’s stepping down at Gray’s request to make way for Lew. He displayed no sour grapes: “I totally understand if the mayor wants to make a change,” he said, adding that Lew will give the chairman’s job “the leadership and the influence it needs.”

He warned, however, about the prospect that the board might devolve from its current model of cooperation into a D.C.-dominated entity rife with interjurisdictional rivalries, gripes and resentments — a la the Metro board. Walker added that he believes Lew understands the value of the current balance.

“The reason that the D.C. Water board works so well is that we’ve approached this as, what works best for D.C. Water is what’s best for D.C. Water,” he said. “Rather than everybody looking at what’s best for each jurisdiction, everyone comes together and looks out at what’s best for the enterprise.”

Walker took a bow, noting that under his leadership, that enterprise has been “truly transformed.”

“I get to go out on top,” he said.