Cypress Forest Public Utility District (PUD) issues: flooding, Raveneaux, parks
Purpose of this page
As a result of flooding in recent years, HCFCD (Harris County Flood Control District) has been under pressure to mitigate flooding along Cypress Creek, which had been largely neglected in previous flood planning. An important part of the HCFCD solution is to build detention basins. For this purpose, HCFCD bought 27 acres from the now-defunct Raveneaux Country Club, including the clubhouse, in anticipation of buying at least the rest of the golf course property that was leased from our Cypress Forest PUD. But there are four competing interests for the PUD land: HCFCD that wants detention basins; the Harris County Parks Department that would like a “linear park” to connect up parks all along Cypress Creek; our own community for the existing park and adjacent “natural” park-like land; and potential community or recreation facilities, possibly including another golf course. It would be difficult to impossible to satisfy more than two of these goals within the acreage, so careful planning will be needed.
The purpose of this page is to summarize the existing situation and explore the impacts of various options for flood water detention basins in Champion Forest. Calculations are based on approximate topographic map data, and general design principles that HCFCD would follow. The tools used here are intended to help with planning: the scenarios can be changed to evaluate different options for locating water detention. Criteria include the amount of flood water that can be detained, the amount of material to be excavated, and the resulting community disruptions such as truck traffic, along with project completion time. While people want better flood control, the benefits of specific projects must be balanced against the cost.
That cost, besides tax dollars, is also in terms of any destruction of Cypress Forest Park or adjacent leased but unused land that provides trails in a natural setting (termed by one resident as a “national park experience”), and other recreational areas and facilities. The leased land area is the most at risk. For detailed examples from the existing leased land, please see the leased land tour . Some pictures from the leased land are sampled below:
Some of the detention basin cases may also threaten parts of the Cypress Forest Park. The following are some pictures from the Tour of Cypress Forest Park:
Besides the loss of a beautiful recreation area adjacent to our homes, a significant cost is the destruction of Champion Forest property values because the projects could take up to 10 years with heavy truck traffic and dust, with trucks passing on Cypresswood every 2 minutes in the first specific HCFCD proposal. This might also lead to road damage
7-10 years is an optimistic estimate based purely on engineering considerations. In the real world, additional delays get added because of delays in project funding or execution due to budget shortfalls, reviews and permitting at all levels of government, cost overruns, subcontractor problems, priority changes due to political changes, unexpected technical issues, environmental surprises, archaeological discoveries, etc. A major risk to the community is that a large project never finishes because of these kinds of delays. If projects halt when halfway done, we could end up with a giant muddy mess of inaccessible clear-cut land and no flood control. One way to reduce these risks is a series of smaller projects that can be completed separately one after the other.
Planning also includes development of parks or other facilities, even landscaping and creating trails, which will result in additional costs for us. HCFCD is in the business of flood control, not park or golf course construction and management, landscaping, trail development, wildlife preservation, or aesthetics. HCFCD says they are happy to work with other community organizations or businesses to achieve these goals beyond flood control. However, traditionally, they turn it over only at the end of their projects, taking little input during a project.
The tools developed for this study should allow relatively quick estimates of the amount and time of excavation for any proposed land transferred to the county for detention, estimating the benefit to the County and the impact on Champion Forest. Several cases are considered here. If anyone wants to propose some new alternatives, let me know and I could evaluate those. For instance, there have been rumors of proposed modifications to the golf course to lower parts of it to serve as detention beyond what the golf course already provides, as a way to help meet HCFCD goals. The amount of detention could be determined with better accuracy than back-of-the-envelope calculations.
The 2018 Harris County Flood Control Bond Issue and the 2020 Baker Study
In August, 2018, Harris County voters approved $2.5 billion in bonds to finance flood damage reduction projects. This covered funding for a lot of projects that had already been defined, and for which plans were already available. Unfortunately, few of these projects were for the Cypress Creek watershed: the County had mostly focused on other areas for years. This meant that Cypress Creek projects had to await planning studies, while construction could start sooner in other areas,
To make progress with Cypress Creek, HCFCD commissioned a Regional Drainage Plan Update, which was released in February, 2020 (the “Baker Study”). This identified multiple sites for flood water detention basins. The purpose of water detention basins is for short-term accumulation of water only during flood events. This “flattens the curve” of flood flows and heights over time, lowering the worst case flood level, so that fewer structures are flooded. They reduce flooding downstream of the basins. The Baker Study’s recommended alternative defined 9 basins costing $641,991,295. This work will take well over 10 years.
One detention basin site replaces the Raveneaux Country Club, including associated land leased from the Cypress Forest PUD. The study found that 232 acres could be used to store 5207 acre-feet of water. That is a very large basin. As found later on this page, even a smaller basin about half that size (2603 acre-feet) would take 7-10 years just to excavate, with disruptive dust and trucks passing on Cypresswood about every two minutes.
The County prepared a promotional video for PR purposes that ignored some site realities such as the existing ground water pumping stations and storage facility for the PUD. The County also constructed an online questionnaire for county-wide use and held a small meeting at Raveneaux. Both the questionnaire and the meeting essentially asked people if they wanted flood control, but without mentioning the impact on the immediate community. Of course people said yes they want flood control-- especially people living outside of Champion Forest, who would not care about the local impact. When the scope of the impact became clearer, Champion Forest held a community meeting at Brill Elementary School, attended by at least 800 people. There was intense concern, and an almost unanimous reaction against the possible detention basin, especially when it was discovered that only 10 houses in Champion Forest might benefit. HCFCD did not attend that meeting, and continues to cite the broad-area survey and Raveneaux meeting as evidence that the local community supports detention basin plans.
The PUD land
Building a proposed detention basin would require HCFCD to take over existing PUD land. The following map shows the PUD properties and adjacent areas. The PUD acquired 258 out of 285 acres from the Raveneaux Country Club in 2011, with a leaseback arrangement for 206 acres. 27 acres including the Raveneaux clubhouse and nearby facilities were not purchased by the PUD. The purchase was made with a bond issue approved in 2008, with the goal of maintaining green space. The bonds were issued with the understanding that Champion Forest would end up with a park, and a 9-hole golf course would remain in operation. Under the leaseback arrangement, if the Raveneaux owners failed to maintain a golf course, their lease would terminate forever.
(Click the picture to get a full-sized zoomable image) The following is the corresponding satellite view, which shows a little more of the surrounding area, including the water treatment plant at the far right (east) end. Railroad tracks are at the left (west) end. Those tracks have been mentioned by HCFCD as a possible place to load dirt excavated from a detention basin, although there are no visible sidings available for this yet.
(Click the picture to get a full-sized zoomable image)
Experience with other flood control basins
Here, we look at other projects, to get an idea of what the results might look like, and how long they take.
Kuykendahl stormwater detention basin (HCFCD)
This HCFCD project in on a 288-acre property near Kuykendahl Road and Ella Boulevard. It is intended to hold a smaller volume on a bigger parcel of land than a Raveneaux basin (see table, later). There also is not as much setback from homes as has been promised for Raveneaux. As a result, there was more room for “softening” the appearance with islands, peninsulas, plantings, and gentle slopes than there would be at Raveneaux. The Raveneaux basin would have to be more “industrial” looking as a result. The HCFCD project description is at https://www.hcfcd.org/Find-Your-Watershed/Greens-Bayou/Kuykendahl-Stormwater-Detention-Basin for details. A construction contract was awarded in June, 2015. The intent was for the construction to be done in 3 years. It is now 5.5 years later, and the project is not done. Note that beautification steps like planting trees are only started after construction. Total project time is much longer, because of everything needed before construction starts, and beautification work done after the construction. Here is what it looked like at various times. In February, 2020, after 4.7 years, construction was not complete. By June, 2021, (after 5 years of construction), one area had several hundred 3-5 foot tree saplings. But other construction is not complete.
Exploration Green Detention Facility (Clear Lake City Water Authority)
The Exploration Green detention ponds in Clear Lake City have been held up as an example of conversion of a 178 acre golf course to detention basins for flood control. This is a series of projects in progress by the Clear Lake City Water Authority (CLCWA), not HCFCD There is also a separate volunteer-driven non-profit organization behind this, called the Exploration Green Conservancy (EGC). EGC is responsible for beautification. Planning started in 2005, with a master plan introduced in 2013. Construction started in 2015, following a 6 year battle to condemn the property. Completion is expected in 2021. Like Raveneaux, the golf course had gone bankrupt. The owner wanted to develop it as real estate, and the community objected. This project achieved national recognition, for example, this article in the Washington Post. It was cited as good example of re-purposing all the failing golf courses that were becoming available. Undoubtedly, HCFCD and Harris County also want to take over golf courses wherever possible. They would see golf courses as large parcels of undeveloped, mostly-cleared land, that are easy targets from both a financial and political standpoint. See the later comments on the TC Jester Stormwater Detention Basin which is adjacent to the Northgate Country Club.
The CLCWA work is now complete for phases 1 and 2: the 80% point in the diagram below is defined as the completion of everything but wetland and tree planting. All plantings are considered done for phase 1. So the phase 1 picture below is as good as that section will look except for future volunteer work by EGC. The permanent water depth is 6 feet, with storage above that of 13 additional feet. The basins are barren compared to the current look of the PUD land. The basins after the one built in the first project phase are constrained to be roughly rectangular. However, there are a few islands and peninsulas. The islands are of particular benefit to the wildlife, especially water birds and alligators. Walking is crowded because, like the Kickerillo-Mischer park, the water forces everyone to walk on one path around each rectangle. There is little sense that you're walking in nature. A few small, scrawny trees have been planted, but it will take 20-40 years for them to match the trees we have now in our park and leased land. If we build basins, we should emulate the CLCWA approach of splitting up the work into a series of separate projects. This was explicitly done to minimize noise and better manage construction traffic. It also reduces the risk of running out of funds in the middle of one big project.
Kickerillo-Mischer Park (Harris County Park System) -- we won’t get a flood control project that looks as good as a park like that
Kickerillo-Mischer Park is a Harris County park that is not for flood control. Its area is used for recreation and beauty, although it would hold some temporary flood water storage. As a result, it is more natural and much prettier than flood control basins, except for the end along Highway 249. Some have hoped that a Raveneaux basin might look like this. The Kickerillo-Mischer park is mentioned here to remind everyone that a Raveneaux basin will not look like this. Using the limited area for flood control at Raveneaux will result in a more “industrial” look, as seen in the pictures of other flood control basins. The water level in the park is higher than it would be the case for pure flood control. Also, as seen in every other project, HCFCD or other flood control districts will essentially clear cut the entire area at the start of a project. Then, only at the end, there will be planting of grass and a few saplings. Any other beautification would have to be negotiated and paid for by other organizations. Recovering even in some areas to achieve the look of the mature forest like parts of Kickerillo-Mischer Park might take 30-40 years. There are also problems even at Kickerillo-Mischer Park. One problem is that the large amount of parking draws in people and crime. Recent postings on NextDoor indicate a lot of car break-ins, for example. We want a mostly private community park. Another problem is that there is so much water that there is one main path around the lake, with only a few significant side areas. That forces everyone on the same path. As a result, it is too crowded. This problem would be even worse at Raveneaux, where the basins have to occupy most of the land to be able to meet the goals for flood storage. Having giant basins would crowd out the trails. Smaller ponds like we currently have give people many more paths between ponds, and nice areas to walk around and explore, but there won’t be room for that. On our existing land, people can walk along paths not that far from each other, but not really see each other, if we don't mow down all the vegetation between trails.
TC Jester Stormwater Detention Basin (HCFCD)
The TC Jester Stormwater Detention Basin will be on either side of TC Jester Boulevard south of Cypresswood Drive, on 171.5 acres of land, as shown in the adjacent map.
To speed up the project, clearing and excavation began on November 18, 2020 for the area west of TC Jester. The portion of the property east of TC Jester is still in the preliminary engineering phase. The work on the west side is planned to take 3 years. The property to the west is the much smaller section: the amount of material for excavation is stated on the HCFCD web site as only 300,000 cubic yards. The splitting of this into 2 separate portions shows that HCFCD can be flexible in allowing multiple phase projects.
The east portion preliminary engineering has been held up awaiting funding from the state using federal government funds. Note that the east section also borders the Northgate Country Club. This would be just pure speculation, but perhaps the County is also waiting for a chance to acquire that golf course. Raveneaux is different, though, because all but 27 acres are already owned by the PUD, not a more easily influenced private owner.
The project lifecycle for flood control projects and the realities
HCFCD publishes a Flood Damage Reduction Project Lifecycle:
The total project time will always be a lot more than just the construction time, as shown on the diagram. There are also delays for things not really emphasized on this diagram, such as government reviews, obtaining permits, or changes in political priorities. Another thing to keep in mind is that HCFCD projects will not include planning or funding for beautification steps, park facilities, and so on. HCFCD only assumes basic maintenance for functionality such as keeping enough grass alive for erosion control, mowing the grass, and keeping pipes unclogged.. HCFCD will work with other organizations after their project completion to achieve other goals, but that will not happen without proactive work and funding by other organizations.
Funding issues could lead to a lot of variability in project schedules. Bond issues such as the 2018 Flood Control Bond Issue, as well as state or federal grants can provide funding over multiple years. So, money can be found for favored projects as long as they fit within the larger scope of the bond or grant. Conversely, projects can also be delayed while waiting for funding from state or federal agencies. But it is important to recognize that priorities can change from year to year, and money originally expected for continuing work on one project might get diverted to another project. Plans can change despite original assurances unless conditions are built into legal agreements.
Steps shown on the diagram can be significantly shortened or lengthened. Projects can also be split into multiple phases, each at a different point in the diagram.
In the case of Raveneaux, the Baker study was the feasibility study. However, the next significant step was property acquisition, purchasing the 27 acres from the Raveneaux owner. The preliminary engineering phase appeared to be minimal, including commissioning the production of a video for PR purposes. When glaring problems were pointed out in the video, the response was it didn’t really represent engineering effort. HCFCD also purchased some land behind unused office buildings along Cypresswood, adjacent to Meyer Park, the PUD water treatment plant, and PUD land, possibly in anticipation of combining it with either a flood basin or the linear park.
In the case of the TC Jester basin, HCFCD is splitting the work into two parts, to speed the project. As noted, the area west of TC Jester is being cleared and excavated now.
Changes in project plans are not unusual in any business or government agency, and not unique to HCFCD for flood control. In the case of the Exploration Green project in Clear Lake City, the timing and the order of project phases were modified based on flooding experience. Unexpected delays arose because of unexpected permitting issues, in their case including getting a variance from Ellington Field prohibiting nearby projects that would attract waterfowl. Delays also arose because of jurisdictional issues with a waterway controlled by HCFCD, which led to splitting phase 3 into two parts.
Flood plains and floodway for Champion Forest
The following map shows the floodplains and floodways in our area along Cypress Creek. This includes the 100 year floodplain in light blue (1% chance of flooding in a year) and additional land in the 500 year floodplain in light green (0.2% chance of flooding in a year). The dark blue indicates the floodway, meaning land that conveys most of the flood water, flowing quickly. It is expected that what is shown as 500 year floodplain in this map will soon be included in an updated definition of the 100 year floodplain.
(Click the picture to get a full-sized zoomable image)
HCFCD’s surprise purchase of land with the Raveneaux clubhouse and the horrifying detention basin proposal
HCFCD surprised us by buying the 27.63 acres of land owned directly by the Raveneaux Country Club. That land includes the clubhouse, tennis courts, parking lots, and maintenance sheds. The county indicated it wanted to buy more land from the PUD, including the acreage leased by Raveneaux. Some of that leased land is used in the current golf course, and some of it is not, providing an extension of the “manicured” Cypress Forest Park that is more natural with more diverse vegetation and wildlife. HCFCD would create a large detention basin on the property it ultimately acquires.
Probably in response to community concerns, HCFCD proposed a detention basin somewhat scaled back from the basin proposed in the Baker Report. Verbal assurances were given that detention basins would be set back 300 feet from Cypresswood, so they could be hidden by trees and better preserve the character of the neighborhood (if someone planted trees)
The county proposal is shown below as “County Plan 1”. It was said to hold 3100 acre-feet of flood water. With our possibly more “gentle” design assumptions, we calculated 2603 acre-feet of flood water storage. The impact of excavating even for the 2603 acre-feet was horrifying for Champion Forest. (See the “County Plan 1 Results Table” later). It would destroy a large amount of beautiful recreational area. Depending on assumptions made the project could take 7-10 years, with dust and large dump trucks entering or leaving Champion Forest every 2.2 minutes. In trade for all this damage to our particular community, 10 houses would be saved from floods comparable to our recent ones. And that would be as the result of all the work being done in the County, not just this project. The Raveneaux project would mainly benefit people downstream of Champion Forest. It isn’t clear yet, but there might not be many projects immediately upstream of Champion Forest. Champion Forest is being asked to sacrifice a lot for the sake of those living downstream.
This proposal was rejected by the PUD, and negotiations are resuming. The final result of this may be for one or more scaled back detention basins on part of the PUD property, as well as property taken by the County for a “linear park”.
The PUD has monthly meetings the first Tuesday of each month. Information from the meetings is posted at https://www.cyforestpud.com/category/latest-news/ . Below, we highlight news about the Raveneaux property in more detail, from the PUD meetings or other sources.
Status as of the PUD meeting Dec 1, 2020
On January 31, HCFCD will take possession of the 27 acres of land they bought from Raveneaux. They intend to “secure” the property, which presumably includes closing up the buildings, turning off the power and phones, and blocking access to the parking lots. HCFCD had previously indicated that it would eventually demolish all the structures, unless the PUD requests otherwise. HCFCD is not allowed to run a golf course. Golf operations are expected to be concluded by the current owner well before January 28, allowing time for disposal of golf carts, maintenance equipment, and so on. The Raveneaux owner is expected to donate the 99 year lease back to the PUD before the end of the year.
A PUD property appraisal was completed, providing a basis for discussions on property sales or exchanges. The PUD met with HCFCD again on November 11, but the PUD is still waiting to hear a new proposal.. The County is willing to swap the 27 acres of Raveneaux land they bought for some other acreage to be used for detention. That was part of why an appraisal was done, to figure out how much land could be given up to achieve an "even" trade.
The County is in the awkward position of having bought a small amount of land (27 acres) that by itself isn't enough to be useful. It seems likely that HCFCD wouldn't want to risk having to sell it at a possible loss, although selling it to a developer is somewhat of a threat. (The main reason for the 2008 Champion Forest bond issue that led to the purchase of most of Raveneaux was to prevent development on most of the land, preserving green space for parks and golf). The County has a political need to show progress on Cypress Creek flooding, so they'll undoubtedly propose something. The County also has the implied threat to try to use eminent domain to seize the land they want. However, my understanding is that it is harder to seize land from another government entity than it is from private owners.
There have also long been rumors that someone will propose an alternative use of the land for a new golf course. But it was made clear at this PUD meeting that there hasn't been any specific proposal made to the PUD. It's getting late to introduce new solutions - the PUD will have to make decisions soon on how to respond to the County, and an agreement with the County might make a golf course impossible. Planning is getting more difficult for the PUD due to the uncertainties. Contingency plans are being drawn up for how to handle mowing, watering, and other maintenance under several possible scenarios. An example brought up at the PUD meeting is that there is an ongoing project for delivering recycled water from the sewage treatment plant, which originally had Raveneaux as a customer. It is time to specify the design for pipe and pump sizing and location. If the whole area becomes a detention basin, the current golf area is no longer a customer. To the extent that part or all of the area becomes park or a new golf course, that area is still a customer. The uncertainty is expected to be addressed by designing for the highest possible consumption under all scenarios, although this may add somewhat to the costs.
A question came up: could the PUD legally run a golf course? The answer from the PUD attorney was that no, that is not legal.
Status update from PUD meeting Jan 5, 2021
On December 10th, the PUD received a draft proposal from HCFCD. The county proposed trading their 27 acres for 140 acres owned by the PUD. The 140 acres would include all of the 35 acres east of Champion Forest Drive, and 105 acres west of Champion Forest Drive, along Cypress Creek. It is thought that all the acreage east of Champion Forest Drive and perhaps 5 acres west of Champion Forest Drive would become part of a “linear park” ultimately connecting up Meyer Park with Kickerillo-Mischer preserve (and beyond). That would leave about 100 acres west of Champion Forest Drive to be used for a detention basin.
The PUD rejected this offer. Discussions with HCFCD will continue. In the meantime, the PUD will be discussing proposals from two potential golf club operators, starting January 13. Proposals for maintenance of the PUD land in the meantime will be discussed in the February meeting. HCFCD will continue with their plans to secure the area around the clubhouse when they take over their 27 acres.
Analysis of some cases for detention basins
Overview of the case results
Several cases were examined. For each case, we computed figures such as the basin volume, the acreage required, the amount of excavated material, and the number of years to complete just the excavation. The cases are described in more detail later, but key results are summarized in the following table. Some statistics on other projects are also included for comparison purposes.
Years to excavate
County Plan 1
7 to 10
1 to 1.4
4.6 to 6.4
1.5 to 2.1
(Comparison to some existing projects .... )
Kuykendahl stormwater detention basin
Exploration Green (Clear Lake City Water Authority) - master plan
(6 years for 5 phases, after 10 years of planning and legal battles)
TC Jester Stormwater Detention Basin
525 in the west section?
171.5 (total, east + west sections)
25 acres in the west section?
185.9 for area west of TC Jester
300,000 for area west of TC Jester
Planned 3 years for the area west of TC Jester
The “minimum area” for the cases analyzed here is based on the exact amount of land needed just for the water or immediate boundary area. It does not count any required access area, maintenance roads, channels, buffer area for the neighborhood, etc., or practical realities such as a desire for simple property boundaries. So the actual area used by the County will likely be larger. Perhaps some of the additional land required by the County could be addressed as easements on PUD property, rather than outright County ownership, although that might not be the preferred choice of HCFCD. In this table, the area reported for existing HCFCD projects is the actual area reported by HCFCD.
The “years to excavate” is based solely on the time to excavate the dirt and rocks, hauling away material in trucks either 5 days/week or 7 days/week. The assumptions are shown in the detailed spreadsheet images below, but the key ones are as follows: trucks with a capacity of 14 cubic yards, 15 trucks in use, 10 minutes to load 1 truck, 1 hour time to drive and unload a truck, and 10 hours/day of truck usage. These assumptions were held constant for comparison purposes. In reality, for the smaller projects, fewer trucks would be used, so the excavation time would be longer.
The “years to excavate” is only a part of an overall basin project. It does not include all the additional time required for the entire project for design and review, various levels of government review in areas such as environmental as well as flood control, budget review and approval cycles, budget changes during the project, contractor bidding and selection, and so on. All that could easily add years, and usually does.
Calculations for each case are based on topographic map data in a 100 foot grid superimposed on a satellite photo
The calculations all start with topographic map data, as elevations above sea level, in feet. These elevations are entered into a grid of 100 x 100 foot squares. The map images that follow show the elevations. Those images are snapshots of a spreadsheet, with the 100 foot grid superimposed on a background satellite image. You can zoom in on the images to better read the elevations in feet, or other features. Elevations from topographic maps are entered in selected grid squares, and interpolated for the remaining grid squares. (Minimal data is entered in many areas outside of the basins, since that does not affect the basin results).
In the gridded maps that follow, areas of possible detention basins are marked with blue background. There are constraints on where detention can be placed. For instance, the county has agreed to set back any detention basin at least 300 feet from the road or houses. Also, HCFCD now has a general policy of not building berms for elevated water detention. The maximum height for the detention basin is chosen to be roughly consistent with the terrain, although some dirt may need to be moved in some areas to achieve this. Areas where some fill may be needed are generally along Cypress Creek, and are indicated with a solid brown background. Since the grid size is 100 feet, but the actual width of this barrier might be less than that, the amount of flood water stored may be somewhat greater than calculated here.
The calculations for each case include the maximum volume of water stored and the volume of excavated material. The material to be excavated is not necessarily the same as the basin volume - it depends on the current elevations. As an example, imagine that the boundaries for a basin have been chosen. If there is a large hill inside those boundaries, just removing material in the hill down to the level of the boundary will not add any flood storage volume.
Based on the material excavated, we calculate the number of dump truck loads. With additional assumptions (that are easily adjusted in a spreadsheet) we then calculate the number of years to complete the excavation, the number of trucks per hour, and so on.
The depths for each grid square in the detention basin are calculated, as deep as possible consistent with constraints on the slope steepness and bottom depth. HCFCD guidelines for detention basins require that the steepest slope must have at most 1 foot vertically for 3 horizontal feet. In addition to erosion concerns and suitability for mowing, this is also partly for safety reasons: making it easier for people to escape if they fall into water. The calculations here assume a more gentle slope on average of 1 vertical foot per 4 feet horizontally. This leaves room for horizontal “shelves” for trails, which is common in projects combining detention with recreation. HCFCD says that their normal practice is the 1:4 slope.
The lowest elevation in the basin is also constrained to ensure drainage. A pure detention basin is supposed to dry out after a flood. So, the design assumes no depth lower than the normal level of Cypress Creek, plus some sloping above that level to ensure drainage. The basin can be dug deeper than that, if we want to have permanent ponds below the drainage level. Ponds will not help with flood control, but are generally considered more attractive. So the calculations are only to show the minimum amount of dirt to be excavated. To have ponds, we would need more truck loads of dirt removed.
It turns out that for the 1:4 slope, with the 100 foot grid size, most of the basin grid cells are at the lowest depth consistent with drainage, rather than being constrained by the slope. If the county assumed a 1:3 slope, that would account for some of their higher basin volume estimate.
Results Tables: calculations on detained water volumes, excavation areas and volumes, and resulting truck traffic and years to completion
The complete set of calculations are shown in Results Tables - click on the Results Tables links associated with each case to see these.
The calculations include statistics on the area used for the detention basin (in square feet and acres), approximate rectangular areas around the basin, the maximum water volume detained in cubic feet and acre-feet, and the amount of material that must be excavated in cubic feet and acre-feet. The basin areas are calculated based only on grid squares marked as basin water or its boundary. The actual amount of land required by HCFCD would be larger to account for channels, maintenance areas, and roads or other access. Some right of way on PUD property may also be required. A plot is also included showing the water detained as a function of water elevation.
Based on the amount of material that must be excavated, then there are calculations including the number of dump truck trips required, the number of years to complete the project based on 5 or 7 days/week of excavation, the number of minutes between trucks entering or leaving the site, and similar calculations. The numbers with green background in the results tables are assumptions made for the calculations, including dump truck size, the number of trucks in the fleet that is used, the time to load a truck, the drive time for one truck round trip including unloading, and the number of hours per day allowed for truck use.
Running all these trucks on public roads will clearly be a major headache. The County has mentioned the possibility of using conveyor belts to move material from the excavation site to railroad cars. However, this is speculative, and requires construction of a railroad siding somewhere that is long enough to handle enough rail cars to wait for trains that can be scheduled between existing train runs. Unless the County could provide an ironclad guarantee that this approach would be taken, we have to consider the worst case: trucks on public roads, mainly Cypresswood or Champion Forest Drive. The County might find it difficult to get involved in upfront guarantees on property usage.
The HCFCD original proposal (“County Plan 1”)
The first proposal from the Harris County Flood Control District (HCFCD) was for a massive detention basin using all the PUD property east of Champion Forest Drive, except for a buffer that included part of the existing Cypress Forest Park. That is, it included all of the current golf course area including the portion with the clubhouse, all of the land leased and used currently for the golf course, and all of the remaining leased land that is unused for golf. The elevation of the top of the basin was set as 106 feet, to match the County proposal. The lowest basin point was also chosen to match the County plans. That is 87 feet at the basin outlet, which is roughly the elevation of Cypress Creek at the outlet at Champion Forest Drive. Basin elevations further west (upstream) are slightly higher to ensure drainage. HCFCD had mentioned the possibility of a wet bottom, which would require additional excavation not considered here.
(Click the picture to get a full-sized zoomable image)
Note that the detention basin is set back typically about 500 feet from Cypresswood for the eastern portion of the basin. This preserves the Cypress Forest Park ponds parallel to Cypresswood and the paths around them. But if the Harris County Flood Control District (HCFCD) only honors their commitment to leave a 300 foot buffer between the road and a detention basin, more area would be dug out, no longer part of the park. A portion of the ponds parallel to Cypresswood would be dug out and drained: detention basins need to be dry except optionally at the very bottom, to provide room to temporarily store flood water. Our optimistic assumption may partly account for why the county found room for more water detention than our analysis.
Calculations related to excavation (“Results Tables”) for this original county proposal follow. The areas 1 through 4 in all the cases are rectangles defined for more detailed results, not really informative for the cases so far. Area 1 contains the northwest corner of the PUD land (area north of Cypresswood. Area 2 contains the rest of the PUD land west of Champion Forest Drive. Area 3 contains the PUD land east of Champion Forest Drive. Area 4 contains land west of Area 1. The second table in the results (“Land needed for basin area by containing rectangular area”) shows the acreage for these areas. That table is included only to help visualize the sizes of the land areas. It is not part of the results particular to each case.
(Click the spreadsheet snapshot above to get a full-sized zoomable image)
Alternative Plan: Northwest 1
(Click the picture to get a full-sized zoomable image) This is the northwest portion of the County Plan 1, included mainly for completeness. Although it is relatively small, it may be possible to combine it with adjacent land that is already owned by the County, or could be purchased by the County.
The smallness is a big advantage for us: it means a smaller project that is more likely to be completed. A big risk on larger projects is that they get abandoned or severely delayed mid-project. Land could get cleared and massive holes could be dug, and then just left as muddy holes in the ground.
The County had mentioned that it is no longer interested in this section, even though it was considered useful in the original plan. The reasons are unknown. We could propose it again and renew their interest.
Calculations related to excavation for this case are at Alternate Plan Northwest 1 Results Tables .
Alternative Plan West 1
(Click the picture to get a full-sized zoomable image) This is the western portion of County Plan 1.
Calculations related to excavation for this case are at Alternate Plan West 1 Results Tables .
This has the advantage that it has no impact on the existing Cypress Forest Park or adjacent “natural” area that is leased but unused for golf. It also would avoid the budget increase that would be required if the PUD had to start maintaining all this area formerly managed by Raveneaux. It also has the advantage that it could be naturally staged as two smaller projects, reducing the risk of one large project abandoned part way through.
As in the “Northwest 1” plan, there is the possibility for the County to combine this land with land the County already owns, or could purchase.
Alternate Plan East 1
(Click the picture to get a full-sized zoomable image) This is on land east of Champion Forest Drive. Besides PUD land, it also includes some land already owned by the County at the west end of the developed portion of Meyer Park, and assumes that the County could buy or condemn a small amount of land behind some mostly-empty retail space along the south side of Cypresswood, between Dry Gully and Meyer Park. The retail properties flooded during Hurricane Harvey, and are still mostly unrented. Perhaps the County could buy those as well, although that is not included here. UPDATE: it turns out that on August 19, 2020 HCFCD bought the land behind that retail space on Cypresswood: about 3.22 acres, paying about $87,083 per acre. This may indicate that they are also thinking about putting detention in this area. We should encourage this! The county-owned area right by the water plant is scenic, with tall trees. However, it is not heavily used because of the smells that come from the sewage treatment plant. This makes it ideal as a detention basin. Most of the PUD land used in this case is not maintained as part of the existing Cypress Forest Park. The existing maintained paths in Cypress Forest Park are preserved. The PUD land east of Dry Gully is very scenic because the trees were never cut down for a golf course. It would be unfortunate to lose this very scenic area, but it is not used extensively by Champion Forest people because it is a little further away, and requires crossing over Dry Gully. Also, it does not appear that the PUD is maintaining their portion of the main trail heading east along Cypress Creek, east of Dry Gully. By the Fall of 2020, in spots there was a tight squeeze between giant ragweed plants.
Calculations related to excavation for this case are at Alternate Plan East 1 Results Tables .