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 built detention basins.
The purpose of this page is to 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. 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. A resulting 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, 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 favor 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, or aesthetics. HCFCD is 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.
Background: 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 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 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, attended by at least 500 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.
Background: the PUD land
(Click the picture to get a full-sized zoomable image) Building the proposed detention basin would require HCFCD to take over existing PUD land. This map shows the PUD properties. The PUD acquired 258 out of 285 acres from the Raveneaux Country Club back 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.
Background: Flood plains and floodway for Champion Forest
(Click the picture to get a full-sized zoomable image) This 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.
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. 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.
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, not just this project. The Raveneaux project would mainly benefit people downstream of Champion Forest. Not much is being done upstream of Champion Forest, so 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.
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 showing elevations and features are snapshots of a spreadsheet, with the 100 foot grid superimposed on a background satellite image. You can zoom in on the image to better read the elevations in feet, or other features. Elevations 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).
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. Based on the material excavated, we calculate the number of dump truck loads. With additional assumptions (that can be 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.
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 probably requires construction of a railroad siding somewhere. 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 plans. 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.
(Click the picture to get a full-sized zoomable image) You can zoom in on either the full-sized image or the thumbnail to the left to be able to read the numbers or other features.
Calculations related to excavation for this case are at County Plan 1 Results Tables.
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 (for unknown reasons). However, it was considered useful in the original plan. We could certainly 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 as part of Meyer Park, and assumes that the County could buy or condemn a small amount of land behind some mostly-empty retail space. These properties flood readily, so they are mostly unrented. The owners may gladly sell some or all of their land. 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 .