6 Ways In-House Hydrology De-Risks Your Solar Project

Hossein Ghoveisi, PhD, - Head of Hydrology, Castillo Engineering

When people think of solar, “water” isn’t the first thing that comes to mind. Water and solar projects are often treated separately, but they should be considered together.

As solar development moves to more constrained and irregular sites, and as major storms grow in both frequency and intensity, keeping the two apart has become a challenge for hydrologists.

Addressing hydrology inadequately, or too late, often leads to costly redesign and construction impacts. Higher runoff velocities, tighter drainage corridors, and greater sensitivity to small grading changes can lead to project delays, cost overruns, and long-term O&M issues.

Fortunately, when hydrology is evaluated early by specialized hydrologists, civil layouts are more likely to remain stable through permitting and construction. Integrating hydrology early and continuously is one of the most effective ways to reduce both upfront and long-term project risk.

As Castillo’s Head of Hydrology, I lead in-house hydrology services tightly integrated with grading and drainage design, giving developers and EPCs construction-ready solutions that reflect real watershed conditions and reduce surprises in the field.

Since in-house hydrology is a unique offering in the utility-scale solar industry, we get a lot of questions on why we offer it, how specifically it benefits solar stakeholders, and what our process looks like.

Here’s our deep dive Q&A about the growing importance of hydrological services for utility-scale solar:

What's the cost of overlooking hydrology?

Many teams underestimate how much off-site watershed conditions drive flood risk. Even when a site passes permitting, that doesn’t mean it’s protected over the full life of the asset. Often, a site can pass permitting and still face operational vulnerabilities over its 30+ year lifespan.

Overlooking hydrology has the worst impact on EPC costs and schedules when drainage conflicts are discovered late. These conflicts force expensive, time-consuming redesigns of:

• Grading

• Access roads

• Trenches

• Construction sequencing

During construction, poor drainage planning can also lead to storm-related shutdowns and the need for erosion repairs. Projects can grind to a halt because runoff patterns weren't modeled accurately, or because temporary grading directed water toward active work areas.

And of course, the longest-lived risk to the project owner is flooding, especially in areas predicted to experience heavier storms over the next few decades. Inadequate hydrology analysis may also create issues with post-construction warranties – all of which could have been prevented with proper analysis.

How do early hydrology evaluations reduce risks?

Floodplain boundaries, runoff patterns, and upstream watershed conditions directly impact grading limits and drainage design. Early, expert hydrology evaluations address and mitigate these potential issues in utility-scale development. Addressing these factors upfront facilitates smoother permitting and prevents delays caused by inadequate flood risk analysis.

After permits are secured, hydrology constraints also influence construction sequencing, access roads, and erosion control. Flooding and storm damage remain ongoing concerns throughout a project's life; designing to mitigate those risks helps protect sites for their decades of operation.

How does good hydrology design and integration benefit developers and EPCs?

For developers, strong hydrology design mitigates the risk of storm and flood damage. This prevents drainage failures that can otherwise render a site non-operational, losing weeks or months of revenue.

Even if some damage occurs, robust hydrological design helps protect developers from liability by demonstrating due diligence to municipal authorities.

For EPCs, good hydrology design means encountering fewer unexpected wet areas, erosion problems, or drainage conflicts. This allows construction crews to work as planned, without frequent field-driven redesigns. The results: lower construction costs, faster earthwork schedules, and fewer post-construction drainage corrections.

How does hydrology affect other stakeholders, like agencies and investors?

For agencies, municipalities, and AHJs, strong hydrology analysis demonstrates that flood risks and downstream impacts have been responsibly addressed, reducing the likelihood of future enforcement actions or mandated retrofits after major storm events.

Owners, investors, and lenders want confidence that assets will remain operational and insurable after extreme weather. Robust hydrology design reduces the risk of prolonged outages, repairs, and compliance issues that could threaten revenue.

Well-designed drainage systems also reduce ongoing maintenance, sediment removal, and access road repairs – all of which impact long-term financial performance models.

Why does Castillo offer in-house hydrology and drainage services?

While most solar engineering firms use third-party contractors for hydrology analysis, I lead Castillo’s in-house hydrology offerings. I work directly with grading and drainage designers to rapidly align watershed analysis, site grading, and drainage as conditions and agency comments change.

We tightly coordinate hydrology modeling with civil grading, drainage, and access planning. When changes are needed, our team can update hydrology and site design simultaneously. This allows us faster, more transparent communication and flexibility regarding site adjustments and updates.

Our EPC and developer clients benefit from fewer hand-offs, dedicated expertise, and customized analyses of all site features. This capability accelerates project timelines and saves costs for Castillo clients:

• Avoids third-party handoff delays

• Minimizes costly and time-consuming redesigns

• Helps EPCs stay on schedule

• Reduces post-construction remediation and warranty risk

Can you share a time when in-house hydrology helped prevent a major construction delay or redesign?

Yes! One of our partners was at an advanced stage of the permitting process when an agency reached out to request additional flood-impact analyses. We updated the hydrology and grading in-house simultaneously, quickly resolving comments without delaying the construction start date.

Once that was resolved, hydrology modeling revealed that early-phase grading would temporarily direct runoff toward active work areas, increasing erosion risk during construction. We recommended designing a swale/channel to safely convey runoff away from construction zones. The team modified interim drainage and sequencing plans so EPC crews could maintain productivity even during storm events, avoiding shutdowns and remediation.

In-House Hydrology: De-Risking Your Solar Project

As flood risks increase from site conditions, storms, and floods, meeting minimum permit requirements isn’t enough. In-house hydrology allows real-time coordination between watershed analysis, grading, and drainage design, enabling faster iteration, smarter cost-to-risk tradeoffs, and solutions that protect both construction schedules and long-term asset performance.

If you’re a developer or EPC, the last thing you need is to worry about flood risks. Our in-house hydrology team will ensure you never have to.

Get in touch with our team to discover how you can benefit from in-house hydrology.