In addition to the huge list of recovery and reconstruction activities, we need to think about our next planning and engineering activities to be better prepared and informed for our next large rain event. There is no engineering solution that will prevent large rain events – so we WILL have another one. Here’s a list of ten list of planning and engineering activities we should undertake:
- Update Rain Event Statistics: Harris County Flood Control District (HCFCD) is currently a funding partner with the National Oceanic Atmospheric Administration’s (NOAA’s) “Atlas 14” effort, which is recalculating all rain event statistics for the entire country. The work for the Texas area is currently underway and we should try to accelerate that effort if at all possible. We also should make sure that the rain events of 2016 and 2017 are included in analysis. This will update the depth of the 1% annual chance, 24-hour event – our design basis for all new infrastructure.
- Estimate Future Conditions: If we graph the frequency of daily rainfall depth measurements over time we see a gradual increase in the frequency of 1″ days, 2″ days, and 3″ days going into the future. We should use this data to estimate how much the 1% annual chance, 24-hour event is increasing each year going into the future. This would allow us to estimate the depth of rain associated with the 1% annual chance, 24-hour event in any future year. This would help inform how we design new infrastructure, which is currently sized to handle about 12.5″ in 24-hours.
- Prepare Cost Estimates: We should estimate the costs associated with infrastructure and development designs that can handle the 0.2% and the 1% annual chance, 24-hour event; 25, 50, and 75 years into the future. This would allow policy makers and tax payers (you and me) to see the cost differences alongside the policy options. These costs should be “life-cycle” costs – that is they should include the initial capital costs plus the future replacement or repair costs (prorated by the probability of loss).
- Discuss Policy Options and Costs: We need to have some robust discussions about our willingness to pay for reducing flood risks. Today, just days after the storm, people seem very willing to pay a lot for nearly zero risk. But as the memory of the storm fades that willingness to pay diminishes. If we present and discuss the cost of achieving a few different levels of risk (say the 0.2% annual chance or the 1% annual chance), then tax payers, elected officials, and interest groups can hopefully reach an informed consensus.
- Invest to Reduce Existing Risks: No planning and engineering effort would be complete without looking at existing risks. We have thousands of homes inside the EXISTING 1% annual chance, 24-hour event floodplains, we have channels and drainage systems that can’t handle the EXISTING 1% annual chance, 24-hour event, much less the estimated future event size. HCFCD has reported a $27 billion cost to upgrade all channels and bayous to handle the 1% annual chance, 24-hour event. The City of Houston and Harris County (and other local governments) would also have costs to upgrade their local drainage systems. In 1999 the City of Houston received an estimate of $2.7 billion for drainage improvement needs. These investments might include buying out structures, elevating structures, channel improvements, drainage system improvements, detention facility construction, roadway flood gauges, underpass warning lights and gates, and many other facilities. We need to make these investments (see Item 7).
- Pick a Risk Level and Update Design Rules: Based on the results of Items 1-5, local governments should pick a common risk level and update their drainage and floodplain management rules. The rule updates could include a variety of measures. We could elevate structures, establish riparian buffers. We could impose larger minimum detention requirements and add minimum volume control requirements (retention) to address not just peak runoff rates, but also increases runoff volumes. We could impose minimum “free-board” requirements (the height difference between the anticipated flood water level [at the selected risk level] and the structure you are trying to protect). We could incentivize or require the use of natural drainage systems (see Item 8 below).
- Increase Spending on Public Drainage Infrastructure, Especially in Older Areas: The current property tax rate allocated to Harris County Flood Control District is $0.02827 for each $100 of appraised value. So if you live in a home appraised at $100,000 your current annual tax payment to Harris County Flood Control District is $28.27 per year. If you live in the City of Houston you would also be subject to the 11.8 cents property tax capture to Rebuild Houston and perhaps another $4.00 per month in the city’s drainage fee (depending upon the size of your property and how much of it was impervious). I think most people would support increasing their contribution to our drainage infrastructure, but see Items 4 and 5 above. Any revenue collection approach could be structured to minimize the burden to lower income citizens and the amount collected should be proportional to the amount of stormwater runoff from each property. Retrofitting under served areas should be our focus. See Item 6 above.
- Use Green Stormwater Infrastructure or Natural Drainage Systems: Traditional drainage uses concrete pipes to move stormwater away from properties quickly. We then store the water in large holes in the ground (called detention basins) and release the water slowly. The release rate is restricted so the flowrate after development is less than pre-development flowrate. This doesn’t control the total volume of runoff, which is a key issue in flooding of flat areas like Houston. We should design stormwater systems to slow the water down and encourage more evaporation, infiltration, and consumption by plants. This green stormwater approach is not a silver bullet, but it would help with flooding issues and it sometimes costs less than traditional systems. Every cubic foot of stormwater we can manage or control where it falls is one less we need to convey or worry about flooding something. I’ve written about this before, here and here.
- Enhance Risk Communication and Citizen Engagement: We have the information and technology to provide citizens with better information about their risk of flooding. The risk of flooding should be communicated during real estate transactions or when someone rents an apartment. We can provide very accurate and timely notifications and warnings to each citizen, home owner, and business. Rainfall estimates, actual rainfall amounts, bayou levels, reservoir release rates, gate status, and other information can be served up to each citizen’s cell phone. We need to set up a system to do this. This might be done using an “op-out” format, so everyone’s signed up automatically. Public safety could be the justification for the op-out approach.
- Implement a Volume Trading Program: Local governments should join together to create, for each drainage area or watershed in the region, a stormwater volume capture target and unit cost for each cubic foot of stormwater. All new projects would then need to comply with the new design rules. The stormwater volume cost would create an incentive to build more detention or capture volume into the project, because any excess could be sold to another party in the same drainage area. This scheme would incentivize building more detention and volume capture facilities which would reduce flooding risks. I wrote more about this in my post about policy options for the new City of Houston “Flood Czar.”
There is no silver bullet to SOLVE Houston’s flooding issues, but these planning and engineering actions would help us all deal with the next large rain event.