[jacket3ree]

I may be the "resident expert" referred to above.*

I haven't looked at Stanford's storm drain master plan in a long time, but it wasn't that long ago that we prepared a regional flood hazard study complete with mapping. Lake Lag was part of the watershed modeling, because we modeled Stanford's system, but nothing stuck out about it in terms of hazard reduction. So, I pulled up Stanford's Detention Master Plan (Nolte, 2001) to see what I could learn/remember/misremember about Stanford's storm drain system and Lake Lag's role therein.

Storm Drainage Detention Master Plan

"A significant drainage feature on the southwestern side of the study area is Lake Lagunita.
The hills generally drain toward Lake Lagunita. The location and drainage area is
specifically noted in Figure 4-1. A storm drain, the Junipero Serra Foothills Storm Drain,
has recently been designed to augment the existing Gerona Ditch to collect flows from the
hills south of Lake Lagunita. The arm of the lake, extending to the west, intercepts flows
from the hills southwest of the lake. Initial flows from very large storm events that
exceed the storage capacity of Lake Lagunita are released by the spillway, and are
captured by a storm drain that is routed to San Francisquito Creek. Flows from the
spillway that exceed the storm drain capacity flow overland across the Campus
northeasterly toward Matadero Creek."


There is natural drainage to Lake Lagunita, so it is storing stormwater runoff that would otherwise run through campus.  I was incorrect - while it was created in the 19th century to hold irrigation water, it does serve a natural drainage control function.  I do not know if anyone has modeled flows with the facility removed to calculate its benefit. It has a spillway (or did in 2001) and if those spilled flows are not captured by a storm drain to San Francisquito Creek, they find their way across campus.  The other lake "outlet" of course is percolation through its sandy bottom, assuming there isn't a layer of silt at the lake bottom preventing that. Right now, the lake level is probably close to local groundwater levels, which are high. My house is barfing water between foundation and adjacent driveway, but it's clear (yea!) and no signs of uplift.  Might be burning up some more sump pumps this spring.  I've gone swimming down below before.....

Someone asked about what happens if the embankment fails. Ans: with a full lake and catastrophic failure; wall 'o water. However, Lake Lagunita is a California Jurisdictional Dam, so the Division of Safety of Dams performs regular inspections. If they felt the embankment is unsafe, they would make Stanford retrofit the facility or remove it completely.  

California Jurisdictional Dams

*On the advice of my professional liability insurance broker, I am not an expert. I am a professional engineer exercising that degree of care and skill ordinarily exercised under similar circumstances by members of its profession performing the kind of services herein and practicing in the same or similar locality at the same time.

(TLDR: I'm just another know-it-all yahoo on the internet, so the bar for y'all to come after me is super low high.)

[jacket3ree]

I may be the "resident expert" referred to above.*

I haven't looked at Stanford's storm drain master plan in a long time, but it wasn't that long ago that we prepared a regional flood hazard study complete with mapping. Lake Lag was part of the watershed modeling, because we modeled Stanford's system, but nothing stuck out about it in terms of hazard reduction. So, I pulled up Stanford's Detention Master Plan (Nolte, 2001) to see what I could learn/remember/misremember about Stanford's storm drain system and Lake Lag's role therein.

Storm Drainage Detention Master Plan

"A significant drainage feature on the southwestern side of the study area is Lake Lagunita.
The hills generally drain toward Lake Lagunita. The location and drainage area is
specifically noted in Figure 4-1. A storm drain, the Junipero Serra Foothills Storm Drain,
has recently been designed to augment the existing Gerona Ditch to collect flows from the
hills south of Lake Lagunita. The arm of the lake, extending to the west, intercepts flows
from the hills southwest of the lake. Initial flows from very large storm events that
exceed the storage capacity of Lake Lagunita are released by the spillway, and are
captured by a storm drain that is routed to San Francisquito Creek. Flows from the
spillway that exceed the storm drain capacity flow overland across the Campus
northeasterly toward Matadero Creek."


There is natural drainage to Lake Lagunita, so it is storing stormwater runoff that would otherwise run through campus.  I was incorrect - while it was created in the 19th century to hold irrigation water, it does serve a natural drainage control function.  I do not know if anyone has modeled flows with the facility removed to calculate its benefit. It has a spillway (or did in 2001) and if those spilled flows are not captured by a storm drain to San Francisquito Creek, they find their way across campus.  The other lake "outlet" of course is percolation through its sandy bottom, assuming there isn't a layer of silt at the lake bottom preventing that. Right now, the lake level is probably close to local groundwater levels, which are high. My house is barfing water between foundation and adjacent driveway, but it's clear (yea!) and no signs of uplift.  Might be burning up some more sump pumps this spring.  I've gone swimming down below before.....

Someone asked about what happens if the embankment fails. Ans: with a full lake and catastrophic failure; wall 'o water. However, Lake Lagunita is a California Jurisdictional Dam, so the Division of Safety of Dams performs regular inspections. If they felt the embankment is unsafe, they would make Stanford retrofit the facility or remove it completely.  

California Jurisdictional Dams

*On the advice of my professional liability insurance broker, I am not an expert. I am a professional engineer exercising that degree of care and skill ordinarily exercised under similar circumstances by members of its profession performing the kind of services herein and practicing in the same or similar locality at the same time.

(TLDR: I'm just another know-it-all yahoo on the internet, so the bar for y'all to come after me is super low high.)